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ZAAPS programme results for 2016: an activity and spectrum analysis of linezolid using clinical isolates from medical centres in 42 countries

ZAAPS programme results for 2016: an activity and spectrum analysis of linezolid using clinical... Abstract Objectives To report the linezolid activity, resistance mechanisms and epidemiological typing of selected isolates observed during the 2016 Zyvox® Annual Appraisal of Potency and Spectrum (ZAAPS) programme. Methods A total of 8325 organisms were consecutively collected from 76 centres in 42 countries (excluding the USA). Broth microdilution susceptibility testing was performed and isolates displaying linezolid MICs of ≥4 mg/L were molecularly characterized. Results Linezolid inhibited 99.8% of all Gram-positive pathogens at the respective susceptible breakpoints and showed a modal MIC of 1 mg/L, except for CoNS, for which the modal MIC result was 0.5 mg/L. Among isolates displaying linezolid MICs of ≥4 mg/L, one Staphylococcus aureus (linezolid MIC of 4 mg/L) harboured cfr and belonged to ST72, while four CoNS (MICs of 16–32 mg/L; ST2) showed drug target alterations. Two Enterococcus faecium (ST117) from a single site in Rome were linezolid non-susceptible (MICs of 8 mg/L) and had G2576T mutations. Eight linezolid-non-susceptible Enterococcus faecalis (MICs of 4 mg/L; 4 sites in 4 countries; ST256, ST480, ST766 and ST775) carried optrA and isolates carrying optrA from the same medical centre were genetically related. One Streptococcus gallolyticus (MIC of 4 mg/L) and one Streptococcus mitis (MIC of 16 mg/L) carried optrA and G2576T mutations, respectively. Conclusions These results document the continued long-term in vitro potency of linezolid. Alterations in the 23S rRNA and/or L3/L4 proteins remain the main oxazolidinone resistance mechanisms in E. faecium and CoNS, whereas optrA emerged as the sole mechanism in E. faecalis. Surveillance and infection control will be important strategies to detect optrA and prevent it from disseminating. Introduction Linezolid was the first-in-class oxazolidinone agent approved for treating Gram-positive infections. Its clinical approval occurred in early 2000 by the FDA and in 2001 by EMA and other regulatory agencies.1 Following regulatory approval, the in vitro activity of linezolid was monitored through several programmes, including Zyvox® Annual Appraisal of Potency and Spectrum (ZAAPS) and Linezolid Experience and Accurate Determination of Resistance (LEADER), which surveyed the drug activity, emergence of resistance and resistance mechanisms, and the epidemiology of selected isolates in a broader scale during 2004–16.2,3 The ZAAPS programme included Gram-positive pathogens responsible for infections in patients from several medical institutions located in many countries worldwide, except for the USA, which was monitored by LEADER. Both programmes reported on the consistent and potent in vitro activity of linezolid and, most importantly, emerging resistance mechanisms, including plasmid-mediated cfr,4,5,cfr(B)6 and optrA.7 These programmes also reported on the complex evolution of the oxazolidinone resistance mechanisms that occurred among CoNS during the last 12 years.1,3 In the final year (2016) of the ZAAPS programme, this study documents the continued evolution of oxazolidinone resistance mechanisms and reports the emergence of optrA in Streptococcus gallolyticus and its presence in Enterococcus faecalis as the most common resistance mechanism. Materials and methods Clinical isolates The ZAAPS programme was part of the SENTRY Antimicrobial Surveillance Program, which monitors antimicrobial resistance and the prevalence of pathogens causing bloodstream infections, community-acquired pneumonia, pneumonia in hospitalized patients, skin and skin structure infections, urinary tract infections and intra-abdominal infections (six main study protocols).2 Participating sites followed instructions specific for each protocol to select and include consecutive and unique (one per patient) isolates that were deemed clinically relevant, based on local criteria, until they reached a target number of 250–500 pathogens per site (depending on medical centre size).2 Isolates that met the selection criteria for each protocol (n = 8325) were initially identified by the participant laboratory (76 centres; 42 countries; 5 continents) using local practices and submitted to the coordinating monitoring laboratory (JMI Laboratories, North Liberty, IA, USA) (Table 1). The monitoring laboratory confirmed bacterial identifications using phenotypic and biochemical methods, per Murray et al.8 All streptococci (non-pneumococci), enterococci other than E. faecalis and Enterococcus faecium, and CoNS were subjected to the MALDI-TOF MS (Bruker Daltonics, Bremen, Germany) system. In addition, all organisms showing questionable phenotypic and/or biochemical results had their identification confirmed by MALDI-TOF MS. Table 1. Geographical distribution of Gram-positive pathogens included in this study (2016) Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Each continent/country submitted the following numbers of Gram-positive organisms. Asia-Pacific: 1730 isolates from Australia (550; 6 sites), Japan (206; 2 sites), Korea (238; 2 sites), Malaysia (100; 1 site), New Zealand (239; 2 sites), the Philippines (66; 1 site), Singapore (109; 1 site), Taiwan (124; 1 site) and Thailand (98; 1 site). Europe: 4828 isolates from Belarus (116; 1 site), Belgium (195; 1 site), Croatia (132; 1 site), the Czech Republic (117; 1 site), France (451; 4 sites), Germany (517; 5 sites), Greece (175; 1 site), Hungary (137; 1 site), Ireland (260; 2 sites), Israel (59; 1 site), Italy (435; 4 sites), Poland (55; 1 site), Portugal (174; 1 site), Romania (79; 1 site), Russia (289; 3 sites), Slovakia (141; 1 site), Slovenia (152; 1 site), Spain (343; 3 sites), Sweden (351; 2 sites), Turkey (259; 2 sites) and the UK (391; 3 sites). Latin America: 1517 isolates from Argentina (249; 2 sites), Brazil (362; 4 sites), Chile (173; 2 sites), Colombia (48; 1 site), Costa Rica (78; 1 site), Ecuador (73; 1 site), Guatemala (104; 1 site), Mexico (192; 2 sites), Panama (125; 1 site), Peru (104; 1 site) and Venezuela (9; 1 site). Canada had 250 isolates from 2 sites. Table 1. Geographical distribution of Gram-positive pathogens included in this study (2016) Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Each continent/country submitted the following numbers of Gram-positive organisms. Asia-Pacific: 1730 isolates from Australia (550; 6 sites), Japan (206; 2 sites), Korea (238; 2 sites), Malaysia (100; 1 site), New Zealand (239; 2 sites), the Philippines (66; 1 site), Singapore (109; 1 site), Taiwan (124; 1 site) and Thailand (98; 1 site). Europe: 4828 isolates from Belarus (116; 1 site), Belgium (195; 1 site), Croatia (132; 1 site), the Czech Republic (117; 1 site), France (451; 4 sites), Germany (517; 5 sites), Greece (175; 1 site), Hungary (137; 1 site), Ireland (260; 2 sites), Israel (59; 1 site), Italy (435; 4 sites), Poland (55; 1 site), Portugal (174; 1 site), Romania (79; 1 site), Russia (289; 3 sites), Slovakia (141; 1 site), Slovenia (152; 1 site), Spain (343; 3 sites), Sweden (351; 2 sites), Turkey (259; 2 sites) and the UK (391; 3 sites). Latin America: 1517 isolates from Argentina (249; 2 sites), Brazil (362; 4 sites), Chile (173; 2 sites), Colombia (48; 1 site), Costa Rica (78; 1 site), Ecuador (73; 1 site), Guatemala (104; 1 site), Mexico (192; 2 sites), Panama (125; 1 site), Peru (104; 1 site) and Venezuela (9; 1 site). Canada had 250 isolates from 2 sites. Antimicrobial susceptibility testing Isolates were tested for susceptibility by broth microdilution using 96-well panels following the CLSI guidelines.9 MIC testing was performed using frozen-form panels manufactured by JMI Laboratories that contained CAMHB (2.5%–5% lysed horse blood added for testing streptococci). Isolates exhibiting initial linezolid MIC results of ≥4 mg/L were re-tested in a 96-well panel containing an extended dilution range (1–128 mg/L) for linezolid. Bacterial inoculum density was monitored by colony counting to ensure an adequate number of cells for each testing event. MIC values were validated by concurrent testing of quality control strains.10 MIC interpretations were based on the CLSI and EUCAST breakpoint criteria, except for tigecycline MIC interpretation to which FDA-approved criteria were applied.10–12 Detecting linezolid resistance mechanisms and epidemiological typing Isolates that showed elevated MIC results for linezolid (MICs of ≥4 mg/L) were selected for further characterization at the central laboratory. These isolate genomes were sequenced on a MiSeq sequencer following the manufacturer’s instructions (Illumina, San Diego, CA, USA). Assembled genomes were subjected to proprietary software (JMI Laboratories) to screen for the presence of cfr, cfr(B), cfr(C) and optrA. DNA sequences associated with 23S rRNA and ribosomal proteins (L3, L4 and L22) were extracted and analysed for the presence of mutations.6,13 Isolates exhibiting linezolid MIC results of ≥4 mg/L had the seven housekeeping genes necessary for assigning MLST (ST) extracted from assembled genomes. In addition, isolates from the same species recovered from the same medical centre were subjected to PFGE analysis.2 Results and discussion The vast majority of Gram-positive pathogens (99.8%) included in ZAAPS 2016 were inhibited by linezolid at the respective breakpoints (Table 2). The central tendency (modal MIC) for linezolid against these Gram-positive isolates was 1 mg/L, except for CoNS against which the linezolid modal MIC result was 0.5 mg/L. This MIC value tendency also remained consistent against staphylococci showing a methicillin-resistant phenotype or E. faecium displaying a VRE phenotype (Tables 2 and 3). All but two streptococci were inhibited by linezolid at ≤2 mg/L. Table 2. Linezolid MIC distributions when tested against species and groups of Gram-positive cocci isolated from five continents Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Bold numbers represent the MIC with the highest number of isolates within a given MIC distribution (i.e. modal MIC). a‘ CoNS’ includes Staphylococcus arlettae (1), Staphylococcus auricularis (1), Staphylococcus capitis (77), Staphylococcus caprae (19), Staphylococcus carnosus (1), Staphylococcus cohnii (4), Staphylococcus epidermidis (588), Staphylococcus gallinarum (1), Staphylococcus haemolyticus (159), Staphylococcus hominis (106), Staphylococcus lentus (2), Staphylococcus lugdunensis (102), Staphylococcus pasteuri (3), Staphylococcus pettenkoferi (3), Staphylococcus pseudintermedius (4), Staphylococcus saprophyticus (27), Staphylococcus schleiferi (1), Staphylococcus sciuri (5), Staphylococcus simulans (10), Staphylococcus warneri (25) and Staphylococcus xylosus (1). ‘Viridans-group streptococci’ includes Streptococcus anginosus (107), S. anginosus group (18), Streptococcus australis (2), Streptococcus bovis group (1), Streptococcus constellatus (17), Streptococcus cristatus (3), Streptococcus equinus (2), S. gallolyticus (44), Streptococcus gordonii (8), Streptococcus infantis (1), Streptococcus intermedius (4), Streptococcus lutetiensis (4), Streptococcus mitis (1), S. mitis group (159), S. mitis/oralis (6), S. mutans (3), S. oralis (2), Streptococcus parasanguinis (27), Streptococcus salivarius (9), S. salivarius group (12), Streptococcus salivarius/vestibularis (11), Streptococcus sanguinis (21) and Streptococcus vestibularis (7). ‘β-Haemolytic streptococci’ includes Streptococcus agalactiae (265), Streptococcus canis (2), Streptococcus dysgalactiae (137), Streptococcus equi (1) and Streptococcus pyogenes (331). Table 2. Linezolid MIC distributions when tested against species and groups of Gram-positive cocci isolated from five continents Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Bold numbers represent the MIC with the highest number of isolates within a given MIC distribution (i.e. modal MIC). a‘ CoNS’ includes Staphylococcus arlettae (1), Staphylococcus auricularis (1), Staphylococcus capitis (77), Staphylococcus caprae (19), Staphylococcus carnosus (1), Staphylococcus cohnii (4), Staphylococcus epidermidis (588), Staphylococcus gallinarum (1), Staphylococcus haemolyticus (159), Staphylococcus hominis (106), Staphylococcus lentus (2), Staphylococcus lugdunensis (102), Staphylococcus pasteuri (3), Staphylococcus pettenkoferi (3), Staphylococcus pseudintermedius (4), Staphylococcus saprophyticus (27), Staphylococcus schleiferi (1), Staphylococcus sciuri (5), Staphylococcus simulans (10), Staphylococcus warneri (25) and Staphylococcus xylosus (1). ‘Viridans-group streptococci’ includes Streptococcus anginosus (107), S. anginosus group (18), Streptococcus australis (2), Streptococcus bovis group (1), Streptococcus constellatus (17), Streptococcus cristatus (3), Streptococcus equinus (2), S. gallolyticus (44), Streptococcus gordonii (8), Streptococcus infantis (1), Streptococcus intermedius (4), Streptococcus lutetiensis (4), Streptococcus mitis (1), S. mitis group (159), S. mitis/oralis (6), S. mutans (3), S. oralis (2), Streptococcus parasanguinis (27), Streptococcus salivarius (9), S. salivarius group (12), Streptococcus salivarius/vestibularis (11), Streptococcus sanguinis (21) and Streptococcus vestibularis (7). ‘β-Haemolytic streptococci’ includes Streptococcus agalactiae (265), Streptococcus canis (2), Streptococcus dysgalactiae (137), Streptococcus equi (1) and Streptococcus pyogenes (331). Table 3. Activity of linezolid and comparator antimicrobial agents when tested against Gram-positive clinical isolates as part of the ZAAPS programme (2016) Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 a VGS, viridans group streptococci; BHS, β-haemolytic streptococci. b Criteria as published by CLSI10 and EUCAST,12 except for tigecycline under the CLSI column (FDA). ‘–’ indicates absence of interpretive breakpoint criteria. S, susceptible; I, intermediate; R, resistant. c Susceptibility based on oxacillin results. d Results based on breakpoints for urinary tract infections only. e Using meningitis breakpoints. f Using non-meningitis breakpoints. g Using oral breakpoints. h Using parenteral, meningitis breakpoints. i Using parenteral, non-meningitis breakpoints. Table 3. Activity of linezolid and comparator antimicrobial agents when tested against Gram-positive clinical isolates as part of the ZAAPS programme (2016) Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 a VGS, viridans group streptococci; BHS, β-haemolytic streptococci. b Criteria as published by CLSI10 and EUCAST,12 except for tigecycline under the CLSI column (FDA). ‘–’ indicates absence of interpretive breakpoint criteria. S, susceptible; I, intermediate; R, resistant. c Susceptibility based on oxacillin results. d Results based on breakpoints for urinary tract infections only. e Using meningitis breakpoints. f Using non-meningitis breakpoints. g Using oral breakpoints. h Using parenteral, meningitis breakpoints. i Using parenteral, non-meningitis breakpoints. Comparative analysis showed that linezolid, daptomycin, tigecycline and the glycopeptides were active against MRSA (96.7%–100.0% susceptible) when applying current clinical breakpoints (Table 3). Similar susceptibility results (92.0%–100.0% susceptible) were observed against the entire CoNS collection. Overall, high susceptibility rates (98.5%–100.0% susceptible) were noted for all drugs tested against the E. faecalis collection, except for erythromycin (intrinsically resistant)14 and levofloxacin (for urinary tract infections only).10,12 In contrast, E. faecium exhibited an acceptable (>90.0%) susceptibility rate for linezolid, daptomycin and tigecycline. This species showed a vancomycin non-susceptibility rate of 29.8%. Overall, most agents tested against Streptococcus pneumoniae showed suboptimal coverage (<90.0% susceptible), except for linezolid, amoxicillin/clavulanate, levofloxacin, tigecycline and vancomycin (Table 3). Penicillin and ceftriaxone were active (91.0%–92.9% susceptible) when parenteral breakpoints were applied. The penicillin non-susceptibility rates (penicillin MICs of ≥ 0.12 mg/L) for S. pneumoniae were: Asia-Pacific (APAC) (47.8%) followed by Latin America (36.3%), Europe (29.6%) and Canada (20.0%) (data not shown). Non-susceptibility rates for ceftriaxone (EUCAST breakpoint) were highest in the APAC region (27.8%), with rates of 12.8%–15.6% in the other areas (data not shown). S. pneumoniae displaying non-susceptibility to levofloxacin were only observed in the APAC region (4.1%) and Europe (1.7%). Linezolid, ceftriaxone, daptomycin, levofloxacin, teicoplanin, tigecycline and vancomycin were active against viridans-group streptococci (91.3%–100.0% susceptible) while linezolid, amoxicillin/clavulanate, ceftriaxone, the penicillins, the glycopeptides, daptomycin, levofloxacin and tigecycline had coverage (95.9%–100.0% susceptible) against β-haemolytic streptococci (Table 3). Macrolide resistance was observed in 20.6% of β-haemolytic streptococcal isolates. The nations with macrolide resistance rates of ≥20% were as follows: Argentina (23.1%), Belgium (20.0%), Canada (25.0%), Croatia (20.0%), the Czech Republic (44.4%), Germany (20.0%), Guatemala (23.1%), Ireland (40.7%), Italy (42.4%), Japan (40.0%), Korea (28.6%), Portugal (25.0%), Russia (33.3%), Taiwan (64.3%) and the UK (23.1%). The vast majority (99.9%) of staphylococci were inhibited by linezolid at ≤2 mg/L and one Staphylococcus aureus isolate from Panama City showed a linezolid MIC of 4 mg/L, while four Staphylococcus epidermidis isolates had MIC values of 16–32 mg/L (Tables 2 and 4). The S. aureus isolate carried the cfr gene and belonged to ST72, whereas the four S. epidermidis isolates showed drug target alterations in several sites (Table 4). Multiple oxazolidinone target site alterations have become commonplace among CoNS in the last decade.1,3,S. epidermidis isolates that were non-susceptible to linezolid were mostly from Italy and belonged to ST2; this clonal type represents an important lineage that has been detected in several medical centres worldwide.15 A recent report described the dissemination of ST2 S. epidermidis isolates among Italian medical centres as well.16,17 Table 4. Isolates with elevated or non-susceptible linezolid MIC values (≥4 mg/L) observed during the ZAAPS programme (2016) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) a Typing results where relevant; PFGE performed among isolates from the same species recovered from the same centre; an S. epidermidis with an SEPI377A PFGE profile (ST2) was also detected in 2015 in this site; isolates with an EFM86A (ST117) PFGE profile were also observed in 2002, 2006, 2008 and 2009 in this site. Table 4. Isolates with elevated or non-susceptible linezolid MIC values (≥4 mg/L) observed during the ZAAPS programme (2016) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) a Typing results where relevant; PFGE performed among isolates from the same species recovered from the same centre; an S. epidermidis with an SEPI377A PFGE profile (ST2) was also detected in 2015 in this site; isolates with an EFM86A (ST117) PFGE profile were also observed in 2002, 2006, 2008 and 2009 in this site. A total of eight E. faecalis from Guatemala City (4), Durango (2), Taipei (1) and Paris (1) were non-susceptible to linezolid (MICs of 4 mg/L) and all harboured optrA (Table 4). Isolates recovered from Guatemala City all had the same ST (ST256), as did the E. faecalis from Durango (ST480). Isolates associated with these STs were recovered previously from humans.18,19,E. faecalis isolates carrying optrA usually show genetic lineage diversity with occasional clonal dissemination within medical centres, as reported here and in previous studies.19,20 Only two E. faecium (Rome) isolates were linezolid resistant (MICs of 8 mg/L) and these isolates had 23S rRNA mutations (Table 4). These E. faecium were clonally related (ST117) and the PFGE profile demonstrated by these isolates was observed among linezolid-non-susceptible E. faecium isolates from this site on several occasions (Table 4). One S. gallolyticus (linezolid MIC of 4 mg/L) and 1 Streptococcus mitis (linezolid MIC of 16 mg/L) displayed elevated MIC results for linezolid. While the former carried optrA,13 the latter had 23S rRNA mutations (Table 4). Streptococcal isolates displaying non-susceptible MIC results for linezolid were rarely detected throughout the ZAAPS/LEADER programmes, with one Streptococcus oralis in 2002 (G2576T),21 one S. pneumoniae in 2010 (L4 mutation),22 one Streptococcus sanguinis from 2011 (23S rRNA mutations)23,24 and one S. sanguinis from 2013 (G2576T)25 detected during the programmes’ histories. Other streptococci demonstrating linezolid non-susceptibility were previously reported outside ZAAPS/LEADER,26–28 including the presence of cfr in a Streptococcus suis.28,29 The optrA gene was also previously detected in S. suis isolates recovered from pigs30 and this study reports the emergence of optrA in a S. gallolyticus causing human infection.13 These data show that linezolid has consistent potency against Gram-positive pathogens and emphasize the relevance of surveillance for detecting emerging resistance and for monitoring the evolution of resistance and associated pathogens. The final year of the ZAAPS programme (2016) reports the importance of optrA as an oxazolidinone resistance determinant with its emergence in S. gallolyticus and its dissemination and dominance as a resistance gene in E. faecalis. In previous studies, linezolid resistance among enterococci was mainly due to alterations in 23S rRNA, which remains the case for E. faecium.1 However, optrA has become more common in E. faecalis. This change can be explained, at least partially, by the lack of or a low fitness cost associated with the presence of optrA compared with the presence of mutations in general.31,32 It is interesting to note that cfr has also been associated with a generally low fitness cost in S. aureus,33 and the occurrence of cfr in S. aureus in this study (0.03%) was lower than the presence of optrA in E. faecalis (1.5%). A broader analysis shows that the prevalence of cfr in S. aureus during the last 3 years of LEADER (2013–15) and ZAAPS (2014–16) combined was 0.02% (5/20 349) but 62.5% (5/8) among isolates with linezolid MIC values of ≥4 mg/L.2,3,7 In a similar analysis, the occurrence of optrA in E. faecalis was 0.4% (14/3437) but 100.0% (14/14) in isolates with linezolid MIC values of ≥4 mg/L. cfr and optrA were initially detected in human specimens in these surveillance studies (ZAAPS/LEADER) in 20074 and 2006 (China; R. E. Mendes and L. Deshpande, unpublished data), respectively. These surveillance data suggest that optrA may be disseminating in E. faecalis more rapidly than cfr in S. aureus, implying a greater transferability of optrA.31 Surveillance and infection control will be important strategies to detect and contain the plasmid-mediated optrA resistance gene from disseminating. Acknowledgements We express appreciation to the following persons for technical support and/or manuscript assistance: S. J. R. Arends, L. R. Duncan, L. Flanigan, M. D. Huband, M. Janechek, J. Oberholser, T. Reynolds, P. R. Rhomberg, J. Schuchert, C. Smith and L. N. Woosley. Funding This study was sponsored by Pfizer Inc. Transparency declarations R. E. M., L. D., J. M. S., H. S. S., M. C. and R. K. F. are employees of JMI Laboratories, which received financial support from Pfizer in connection with the surveillance study and development of this manuscript via the SENTRY Antimicrobial Surveillance Program platform. JMI Laboratories also contracted to perform services in 2016–17 for Achaogen, Actelion, Allecra, Allergan, Ampliphi, API, Astellas, AstraZeneca, Basilea, Bayer, BD, Biomodels, Cardeas, CEM-102 Pharma, Cempra, Cidara, Cormedix, CSA Biotech, Cubist, Debiopharm, Dipexium, Duke, Durata, Entasis, Fortress, Fox Chase Chemical, GSK, Medpace, Melinta, Merck, Micurx, Motif, N8 Medical, Nabriva, Nexcida, Novartis, Paratek, Polyphor, Rempex, Scynexis, Shionogi, Spero Therapeutics, Symbal Therapeutics, Synolgoic, TGV Therapeutics, The Medicines Company, Theravance, ThermoFisher, Venatorx, Wockhardt and Zavante. There are no speakers’ bureaus or stock options to declare. P. A. H. is an employee of Pfizer Inc. References 1. Mendes RE , Deshpande LM , Jones RN. Linezolid update: stable in vitro activity following more than a decade of clinical use and summary of associated resistance mechanisms . Drug Resist Updat 2014 ; 17 : 1 – 12 . Google Scholar CrossRef Search ADS PubMed 2. 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Genetic environment of the transferable oxazolidinone/phenicol resistance gene optrA in Enterococcus faecalis isolates of human and animal origin . J Antimicrob Chemother 2016 ; 71 : 1466 – 73 . Google Scholar CrossRef Search ADS PubMed 19. Cai J , Wang Y , Schwarz S et al. Enterococcal isolates carrying the novel oxazolidinone resistance gene optrA from hospitals in Zhejiang, Guangdong, and Henan, China, 2010–2014 . Clin Microbiol Infect 2015 ; 21 : 1095.e1 – 4 . Google Scholar CrossRef Search ADS 20. Cai J , Wang Y , Schwarz S et al. High detection rate of the oxazolidinone resistance gene optrA in Enterococcus faecalis isolated from a Chinese anorectal surgery ward . Int J Antimicrob Agents 2016 ; 48 : 757 – 9 . Google Scholar CrossRef Search ADS PubMed 21. Mutnick AH , Enne V , Jones RN. Linezolid resistance since 2001: SENTRY Antimicrobial Surveillance Program . Ann Pharmacother 2003 ; 37 : 769 – 74 . Google Scholar CrossRef Search ADS PubMed 22. Flamm RK , Farrell DJ , Mendes RE et al. ZAAPS Program results for 2010: an activity and spectrum analysis of linezolid using clinical isolates from 75 medical centres in 24 countries . J Chemother 2012 ; 24 : 328 – 37 . Google Scholar CrossRef Search ADS PubMed 23. Mendes RE , Deshpande LM , Kim J et al. Streptococcus sanguinis isolate displaying a phenotype with cross-resistance to several rRNA-targeting agents . J Clin Microbiol 2013 ; 51 : 2728 – 31 . Google Scholar CrossRef Search ADS PubMed 24. Flamm RK , Mendes RE , Ross JE et al. Linezolid surveillance results for the United States: LEADER Surveillance Program 2011 . Antimicrob Agents Chemother 2013 ; 57 : 1077 – 81 . Google Scholar CrossRef Search ADS PubMed 25. Flamm RK , Mendes RE , Hogan PA et al. In vitro activity of linezolid as assessed through the 2013 LEADER surveillance program . Diagn Microbiol Infect Dis 2015 ; 81 : 283 – 9 . Google Scholar CrossRef Search ADS PubMed 26. Dong W , Chochua S , McGee L et al. Mutations within the rplD gene of linezolid-nonsusceptible Streptococcus pneumoniae strains isolated in the United States . Antimicrob Agents Chemother 2014 ; 58 : 2459 – 62 . Google Scholar CrossRef Search ADS PubMed 27. Farrell DJ , Morrissey I , Bakker S et al. In vitro activities of telithromycin, linezolid, and quinupristin-dalfopristin against Streptococcus pneumoniae with macrolide resistance due to ribosomal mutations . Antimicrob Agents Chemother 2004 ; 48 : 3169 – 71 . Google Scholar CrossRef Search ADS PubMed 28. Wolter N , Smith AM , Farrell DJ et al. Novel mechanism of resistance to oxazolidinones, macrolides, and chloramphenicol in ribosomal protein L4 of the pneumococcus . Antimicrob Agents Chemother 2005 ; 49 : 3554 – 7 . Google Scholar CrossRef Search ADS PubMed 29. Wang Y , Li D , Song L et al. First report of the multiresistance gene cfr in Streptococcus suis . Antimicrob Agents Chemother 2013 ; 57 : 4061 – 3 . Google Scholar CrossRef Search ADS PubMed 30. Huang J , Chen L , Wu Z et al. Retrospective analysis of genome sequences revealed the wide dissemination of optrA in Gram-positive bacteria . J Antimicrob Chemother 2017 ; 72 : 614 – 6 . Google Scholar CrossRef Search ADS PubMed 31. Gawryszewska I , Żabicka D , Hryniewicz W et al. Linezolid-resistant enterococci in Polish hospitals: species, clonality and determinants of linezolid resistance . Eur J Clin Microbiol Infect Dis 2017 ; 36 : 1279 – 86 . Google Scholar CrossRef Search ADS PubMed 32. Meka VG , Gold HS , Cooke A et al. Reversion to susceptibility in a linezolid-resistant clinical isolate of Staphylococcus aureus . J Antimicrob Chemother 2004 ; 54 : 818 – 20 . Google Scholar CrossRef Search ADS PubMed 33. LaMarre JM , Locke JB , Shaw KJ et al. Low fitness cost of the multidrug resistance gene cfr . Antimicrob Agents Chemother 2011 ; 55 : 3714 – 9 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: [email protected]. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Antimicrobial Chemotherapy Oxford University Press

ZAAPS programme results for 2016: an activity and spectrum analysis of linezolid using clinical isolates from medical centres in 42 countries

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: [email protected].
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0305-7453
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10.1093/jac/dky099
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Abstract

Abstract Objectives To report the linezolid activity, resistance mechanisms and epidemiological typing of selected isolates observed during the 2016 Zyvox® Annual Appraisal of Potency and Spectrum (ZAAPS) programme. Methods A total of 8325 organisms were consecutively collected from 76 centres in 42 countries (excluding the USA). Broth microdilution susceptibility testing was performed and isolates displaying linezolid MICs of ≥4 mg/L were molecularly characterized. Results Linezolid inhibited 99.8% of all Gram-positive pathogens at the respective susceptible breakpoints and showed a modal MIC of 1 mg/L, except for CoNS, for which the modal MIC result was 0.5 mg/L. Among isolates displaying linezolid MICs of ≥4 mg/L, one Staphylococcus aureus (linezolid MIC of 4 mg/L) harboured cfr and belonged to ST72, while four CoNS (MICs of 16–32 mg/L; ST2) showed drug target alterations. Two Enterococcus faecium (ST117) from a single site in Rome were linezolid non-susceptible (MICs of 8 mg/L) and had G2576T mutations. Eight linezolid-non-susceptible Enterococcus faecalis (MICs of 4 mg/L; 4 sites in 4 countries; ST256, ST480, ST766 and ST775) carried optrA and isolates carrying optrA from the same medical centre were genetically related. One Streptococcus gallolyticus (MIC of 4 mg/L) and one Streptococcus mitis (MIC of 16 mg/L) carried optrA and G2576T mutations, respectively. Conclusions These results document the continued long-term in vitro potency of linezolid. Alterations in the 23S rRNA and/or L3/L4 proteins remain the main oxazolidinone resistance mechanisms in E. faecium and CoNS, whereas optrA emerged as the sole mechanism in E. faecalis. Surveillance and infection control will be important strategies to detect optrA and prevent it from disseminating. Introduction Linezolid was the first-in-class oxazolidinone agent approved for treating Gram-positive infections. Its clinical approval occurred in early 2000 by the FDA and in 2001 by EMA and other regulatory agencies.1 Following regulatory approval, the in vitro activity of linezolid was monitored through several programmes, including Zyvox® Annual Appraisal of Potency and Spectrum (ZAAPS) and Linezolid Experience and Accurate Determination of Resistance (LEADER), which surveyed the drug activity, emergence of resistance and resistance mechanisms, and the epidemiology of selected isolates in a broader scale during 2004–16.2,3 The ZAAPS programme included Gram-positive pathogens responsible for infections in patients from several medical institutions located in many countries worldwide, except for the USA, which was monitored by LEADER. Both programmes reported on the consistent and potent in vitro activity of linezolid and, most importantly, emerging resistance mechanisms, including plasmid-mediated cfr,4,5,cfr(B)6 and optrA.7 These programmes also reported on the complex evolution of the oxazolidinone resistance mechanisms that occurred among CoNS during the last 12 years.1,3 In the final year (2016) of the ZAAPS programme, this study documents the continued evolution of oxazolidinone resistance mechanisms and reports the emergence of optrA in Streptococcus gallolyticus and its presence in Enterococcus faecalis as the most common resistance mechanism. Materials and methods Clinical isolates The ZAAPS programme was part of the SENTRY Antimicrobial Surveillance Program, which monitors antimicrobial resistance and the prevalence of pathogens causing bloodstream infections, community-acquired pneumonia, pneumonia in hospitalized patients, skin and skin structure infections, urinary tract infections and intra-abdominal infections (six main study protocols).2 Participating sites followed instructions specific for each protocol to select and include consecutive and unique (one per patient) isolates that were deemed clinically relevant, based on local criteria, until they reached a target number of 250–500 pathogens per site (depending on medical centre size).2 Isolates that met the selection criteria for each protocol (n = 8325) were initially identified by the participant laboratory (76 centres; 42 countries; 5 continents) using local practices and submitted to the coordinating monitoring laboratory (JMI Laboratories, North Liberty, IA, USA) (Table 1). The monitoring laboratory confirmed bacterial identifications using phenotypic and biochemical methods, per Murray et al.8 All streptococci (non-pneumococci), enterococci other than E. faecalis and Enterococcus faecium, and CoNS were subjected to the MALDI-TOF MS (Bruker Daltonics, Bremen, Germany) system. In addition, all organisms showing questionable phenotypic and/or biochemical results had their identification confirmed by MALDI-TOF MS. Table 1. Geographical distribution of Gram-positive pathogens included in this study (2016) Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Each continent/country submitted the following numbers of Gram-positive organisms. Asia-Pacific: 1730 isolates from Australia (550; 6 sites), Japan (206; 2 sites), Korea (238; 2 sites), Malaysia (100; 1 site), New Zealand (239; 2 sites), the Philippines (66; 1 site), Singapore (109; 1 site), Taiwan (124; 1 site) and Thailand (98; 1 site). Europe: 4828 isolates from Belarus (116; 1 site), Belgium (195; 1 site), Croatia (132; 1 site), the Czech Republic (117; 1 site), France (451; 4 sites), Germany (517; 5 sites), Greece (175; 1 site), Hungary (137; 1 site), Ireland (260; 2 sites), Israel (59; 1 site), Italy (435; 4 sites), Poland (55; 1 site), Portugal (174; 1 site), Romania (79; 1 site), Russia (289; 3 sites), Slovakia (141; 1 site), Slovenia (152; 1 site), Spain (343; 3 sites), Sweden (351; 2 sites), Turkey (259; 2 sites) and the UK (391; 3 sites). Latin America: 1517 isolates from Argentina (249; 2 sites), Brazil (362; 4 sites), Chile (173; 2 sites), Colombia (48; 1 site), Costa Rica (78; 1 site), Ecuador (73; 1 site), Guatemala (104; 1 site), Mexico (192; 2 sites), Panama (125; 1 site), Peru (104; 1 site) and Venezuela (9; 1 site). Canada had 250 isolates from 2 sites. Table 1. Geographical distribution of Gram-positive pathogens included in this study (2016) Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Organism/organism group Canada Europe Latin America Asia-Pacific Total Staphylococcus aureus 116 2071 902 901 3990  methicillin resistant 31 509 303 296 1139  methicillin susceptible 85 1562 599 605 2851 CoNS 47 667 175 251 1140  methicillin resistant 21 466 131 149 767  methicillin susceptible 26 201 44 102 373 Enterococcus spp. 21 595 162 76 854  E. faecalis 15 352 124 40 531  E. faecium 5 221 30 36 292 Streptococcus pneumoniae 30 726 135 245 1136 Viridans-group streptococci 8 330 43 88 469 β-Haemolytic streptococci 28 439 100 169 736 Total 250 4828 1517 1730 8325 Each continent/country submitted the following numbers of Gram-positive organisms. Asia-Pacific: 1730 isolates from Australia (550; 6 sites), Japan (206; 2 sites), Korea (238; 2 sites), Malaysia (100; 1 site), New Zealand (239; 2 sites), the Philippines (66; 1 site), Singapore (109; 1 site), Taiwan (124; 1 site) and Thailand (98; 1 site). Europe: 4828 isolates from Belarus (116; 1 site), Belgium (195; 1 site), Croatia (132; 1 site), the Czech Republic (117; 1 site), France (451; 4 sites), Germany (517; 5 sites), Greece (175; 1 site), Hungary (137; 1 site), Ireland (260; 2 sites), Israel (59; 1 site), Italy (435; 4 sites), Poland (55; 1 site), Portugal (174; 1 site), Romania (79; 1 site), Russia (289; 3 sites), Slovakia (141; 1 site), Slovenia (152; 1 site), Spain (343; 3 sites), Sweden (351; 2 sites), Turkey (259; 2 sites) and the UK (391; 3 sites). Latin America: 1517 isolates from Argentina (249; 2 sites), Brazil (362; 4 sites), Chile (173; 2 sites), Colombia (48; 1 site), Costa Rica (78; 1 site), Ecuador (73; 1 site), Guatemala (104; 1 site), Mexico (192; 2 sites), Panama (125; 1 site), Peru (104; 1 site) and Venezuela (9; 1 site). Canada had 250 isolates from 2 sites. Antimicrobial susceptibility testing Isolates were tested for susceptibility by broth microdilution using 96-well panels following the CLSI guidelines.9 MIC testing was performed using frozen-form panels manufactured by JMI Laboratories that contained CAMHB (2.5%–5% lysed horse blood added for testing streptococci). Isolates exhibiting initial linezolid MIC results of ≥4 mg/L were re-tested in a 96-well panel containing an extended dilution range (1–128 mg/L) for linezolid. Bacterial inoculum density was monitored by colony counting to ensure an adequate number of cells for each testing event. MIC values were validated by concurrent testing of quality control strains.10 MIC interpretations were based on the CLSI and EUCAST breakpoint criteria, except for tigecycline MIC interpretation to which FDA-approved criteria were applied.10–12 Detecting linezolid resistance mechanisms and epidemiological typing Isolates that showed elevated MIC results for linezolid (MICs of ≥4 mg/L) were selected for further characterization at the central laboratory. These isolate genomes were sequenced on a MiSeq sequencer following the manufacturer’s instructions (Illumina, San Diego, CA, USA). Assembled genomes were subjected to proprietary software (JMI Laboratories) to screen for the presence of cfr, cfr(B), cfr(C) and optrA. DNA sequences associated with 23S rRNA and ribosomal proteins (L3, L4 and L22) were extracted and analysed for the presence of mutations.6,13 Isolates exhibiting linezolid MIC results of ≥4 mg/L had the seven housekeeping genes necessary for assigning MLST (ST) extracted from assembled genomes. In addition, isolates from the same species recovered from the same medical centre were subjected to PFGE analysis.2 Results and discussion The vast majority of Gram-positive pathogens (99.8%) included in ZAAPS 2016 were inhibited by linezolid at the respective breakpoints (Table 2). The central tendency (modal MIC) for linezolid against these Gram-positive isolates was 1 mg/L, except for CoNS against which the linezolid modal MIC result was 0.5 mg/L. This MIC value tendency also remained consistent against staphylococci showing a methicillin-resistant phenotype or E. faecium displaying a VRE phenotype (Tables 2 and 3). All but two streptococci were inhibited by linezolid at ≤2 mg/L. Table 2. Linezolid MIC distributions when tested against species and groups of Gram-positive cocci isolated from five continents Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Bold numbers represent the MIC with the highest number of isolates within a given MIC distribution (i.e. modal MIC). a‘ CoNS’ includes Staphylococcus arlettae (1), Staphylococcus auricularis (1), Staphylococcus capitis (77), Staphylococcus caprae (19), Staphylococcus carnosus (1), Staphylococcus cohnii (4), Staphylococcus epidermidis (588), Staphylococcus gallinarum (1), Staphylococcus haemolyticus (159), Staphylococcus hominis (106), Staphylococcus lentus (2), Staphylococcus lugdunensis (102), Staphylococcus pasteuri (3), Staphylococcus pettenkoferi (3), Staphylococcus pseudintermedius (4), Staphylococcus saprophyticus (27), Staphylococcus schleiferi (1), Staphylococcus sciuri (5), Staphylococcus simulans (10), Staphylococcus warneri (25) and Staphylococcus xylosus (1). ‘Viridans-group streptococci’ includes Streptococcus anginosus (107), S. anginosus group (18), Streptococcus australis (2), Streptococcus bovis group (1), Streptococcus constellatus (17), Streptococcus cristatus (3), Streptococcus equinus (2), S. gallolyticus (44), Streptococcus gordonii (8), Streptococcus infantis (1), Streptococcus intermedius (4), Streptococcus lutetiensis (4), Streptococcus mitis (1), S. mitis group (159), S. mitis/oralis (6), S. mutans (3), S. oralis (2), Streptococcus parasanguinis (27), Streptococcus salivarius (9), S. salivarius group (12), Streptococcus salivarius/vestibularis (11), Streptococcus sanguinis (21) and Streptococcus vestibularis (7). ‘β-Haemolytic streptococci’ includes Streptococcus agalactiae (265), Streptococcus canis (2), Streptococcus dysgalactiae (137), Streptococcus equi (1) and Streptococcus pyogenes (331). Table 2. Linezolid MIC distributions when tested against species and groups of Gram-positive cocci isolated from five continents Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Organism/organism groupa (no. of isolates) No. of isolates and cumulative % inhibited at MIC (mg/L) of MIC (mg/L) ≤0.12 0.25 0.5 1 2 4 8 >8 MIC50 MIC90 S. aureus (3990) 1 23 649 2959 357 1 1 1 <0.1 0.6 16.9 91.0 >99.9 100.0  methicillin resistant (1139) 1 6 232 816 84 1 1 0.1 0.6 21.0 92.6 100.0  methicillin susceptible (2851) 17 417 2143 273 1 1 1 0.6 15.2 90.4 >99.9 100.0 CoNS (1140) 2 81 681 354 18 0 0 4 0.5 1 0.2 7.3 67.0 98.1 99.6 99.6 99.6 100.0  methicillin resistant (767) 1 43 460 242 17 0 0 4 0.5 1 0.1 5.7 65.7 97.3 99.5 99.5 99.5 100.0  methicillin susceptible (373) 1 38 221 112 1 0.5 1 0.3 10.5 69.7 99.7 100.0 Enterococcus spp. (854) 5 155 539 145 8 2 1 2 0.6 18.7 81.9 98.8 99.8 100.0  E. faecalis (531) 4 98 309 112 8 1 2 0.8 19.2 77.4 98.5 100.0  E. faecium (292) 49 214 27 0 2 1 1 16.8 90.1 99.3 99.3 100.0   vancomycin resistant (87) 16 66 5 1 1 18.4 94.3 100.0 S. pneumoniae (1136) 5 153 796 182 1 2 0.4 13.9 84.0 100.0 Viridans-group streptococci (469) 3 16 121 307 20 1 1 1 1 0.6 4.1 29.9 95.3 99.6 99.8 100.0 β-Haemolytic streptococci (736) 33 638 65 1 1 4.5 91.2 100.0 Bold numbers represent the MIC with the highest number of isolates within a given MIC distribution (i.e. modal MIC). a‘ CoNS’ includes Staphylococcus arlettae (1), Staphylococcus auricularis (1), Staphylococcus capitis (77), Staphylococcus caprae (19), Staphylococcus carnosus (1), Staphylococcus cohnii (4), Staphylococcus epidermidis (588), Staphylococcus gallinarum (1), Staphylococcus haemolyticus (159), Staphylococcus hominis (106), Staphylococcus lentus (2), Staphylococcus lugdunensis (102), Staphylococcus pasteuri (3), Staphylococcus pettenkoferi (3), Staphylococcus pseudintermedius (4), Staphylococcus saprophyticus (27), Staphylococcus schleiferi (1), Staphylococcus sciuri (5), Staphylococcus simulans (10), Staphylococcus warneri (25) and Staphylococcus xylosus (1). ‘Viridans-group streptococci’ includes Streptococcus anginosus (107), S. anginosus group (18), Streptococcus australis (2), Streptococcus bovis group (1), Streptococcus constellatus (17), Streptococcus cristatus (3), Streptococcus equinus (2), S. gallolyticus (44), Streptococcus gordonii (8), Streptococcus infantis (1), Streptococcus intermedius (4), Streptococcus lutetiensis (4), Streptococcus mitis (1), S. mitis group (159), S. mitis/oralis (6), S. mutans (3), S. oralis (2), Streptococcus parasanguinis (27), Streptococcus salivarius (9), S. salivarius group (12), Streptococcus salivarius/vestibularis (11), Streptococcus sanguinis (21) and Streptococcus vestibularis (7). ‘β-Haemolytic streptococci’ includes Streptococcus agalactiae (265), Streptococcus canis (2), Streptococcus dysgalactiae (137), Streptococcus equi (1) and Streptococcus pyogenes (331). Table 3. Activity of linezolid and comparator antimicrobial agents when tested against Gram-positive clinical isolates as part of the ZAAPS programme (2016) Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 a VGS, viridans group streptococci; BHS, β-haemolytic streptococci. b Criteria as published by CLSI10 and EUCAST,12 except for tigecycline under the CLSI column (FDA). ‘–’ indicates absence of interpretive breakpoint criteria. S, susceptible; I, intermediate; R, resistant. c Susceptibility based on oxacillin results. d Results based on breakpoints for urinary tract infections only. e Using meningitis breakpoints. f Using non-meningitis breakpoints. g Using oral breakpoints. h Using parenteral, meningitis breakpoints. i Using parenteral, non-meningitis breakpoints. Table 3. Activity of linezolid and comparator antimicrobial agents when tested against Gram-positive clinical isolates as part of the ZAAPS programme (2016) Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 Organism/groupa (no.), antimicrobial agent MIC (mg/L) CLSIb EUCASTb MIC50 MIC90 %S %I %R %S %I %R MRSA (1139)  linezolid 1 1 100.0 –b 0.0 100.0c – 0.0  clindamycin ≤0.25 >2 62.2 0.2 37.6 62.2 0.1 37.8  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin >8 >8 35.2 4.0 60.8 35.6 1.3 63.0  gentamicin ≤1 >8 75.1 0.4 24.5 74.6 – 25.4  levofloxacin >4 >4 35.6 1.4 62.9 35.6 – 64.4  teicoplanin ≤0.5 1 100.0 0.0 0.0 96.7 – 3.3  tetracycline ≤0.5 >8 79.0 0.8 20.2 78.1 0.4 21.5  tigecycline 0.06 0.25 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 96.4 – 3.6 96.4 0.2 3.4  vancomycin 1 1 100.0 0.0 0.0 100.0 – 0.0 MSSA (2851)  linezolid 1 1 100.0 – 0.0 100.0 – 0.0  ceftriaxone 4 8 100.0c – 0.0 – – –  clindamycin ≤0.25 ≤0.25 97.7 0.1 2.2 97.6 0.1 2.3  daptomycin 0.5 0.5 100.0 – – 100.0 – 0.0  erythromycin 0.25 >8 82.0 4.2 13.8 82.7 1.5 15.7  gentamicin ≤1 ≤1 96.2 0.3 3.5 95.8 – 4.2  levofloxacin 0.25 0.25 96.7 0.3 3.0 96.7 – 3.3  penicillin 1 >2 25.8 – 74.2 25.8 – 74.2  piperacillin/tazobactam 1 2 100.0c – 0.0 100.0 – 0.0  teicoplanin ≤0.5 ≤0.5 100.0 0.0 0.0 99.9 – 0.1  tetracycline ≤0.5 ≤0.5 94.8 0.5 4.7 94.3 0.1 5.6  tigecycline 0.06 0.12 100.0 – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 ≤0.5 99.8 – 0.2 99.8 0.0 0.2  vancomycin 0.5 1 100.0 0.0 0.0 100.0 – 0.0 CoNS (1140)  linezolid 0.5 1 99.6 – 0.4 99.6 – 0.4  ceftriaxone >8 >8 32.7c – 67.3 34.8c – 65.2  clindamycin ≤0.25 >2 73.4 1.2 25.4 72.4 1.1 26.6  daptomycin 0.5 1 99.8 – – 99.8 – 0.2  erythromycin >8 >8 40.4 1.8 57.9 40.4 0.7 58.9  gentamicin ≤1 >8 60.5 5.3 34.2 56.7 – 43.3  levofloxacin 0.5 >4 53.6 4.4 42.1 53.6 – 46.4  oxacillin >2 >2 32.7 – 67.3 34.8 – 65.2  piperacillin/tazobactam 2 >16 32.7c – 67.3 34.8c – 65.2  teicoplanin 2 4 99.5 0.4 0.1 92.0 – 8.0  tetracycline ≤0.5 >8 86.1 1.1 12.7 80.1 3.9 16.1  tigecycline 0.06 0.25 – – – 100.0 – 0.0  trimethoprim/sulfamethoxazole ≤0.5 >4 67.9 – 32.1 67.9 14.3 17.8  vancomycin 1 2 100.0 0.0 0.0 100.0 – 0.0 E. faecalis (531)  linezolid 1 2 98.5 1.5 0.0 100.0 – 0.0  ampicillin 1 2 100.0 – 0.0 99.8 0.2 0.0  daptomycin 1 1 100.0 – – – – –  erythromycin >16 >16 11.7 34.6 53.7 – – –  levofloxacin 1 >4 73.8d 0.8 25.4 74.6d – 25.4  piperacillin/tazobactam 4 8 – – – 99.8 0.2 0.0  teicoplanin ≤0.5 ≤0.5 99.6 0.0 0.4 99.6 – 0.4  tigecycline 0.06 0.12 100.0 – – 100.0 0.0 0.0  vancomycin 1 2 99.6 0.0 0.4 99.6 – 0.4 E. faecium (292)  linezolid 1 1 99.3 0.0 0.7 99.3 – 0.7  ampicillin >16 >16 8.2 – 91.8 7.2 1.0 91.8  daptomycin 2 2 99.7 – – – – –  erythromycin >16 >16 5.1 6.5 88.4 – – –  levofloxacin >4 >4 5.1 4.1 90.8d 9.2 – 90.8d  piperacillin/tazobactam >16 >16 – – – 7.2 1.0 91.8  teicoplanin ≤0.5 >16 75.7 9.6 14.7 74.0 – 26.0  tigecycline 0.03 0.06 – – – 99.7 0.0 0.3  vancomycin 0.5 >16 70.2 1.4 28.4 70.2 – 29.8 S. pneumoniae (1136)  linezolid 1 2 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 2 90.8 3.5 5.6 – – –  ceftriaxone 0.03 1 83.6 9.2 7.1e 83.6 14.4 1.9 92.9 5.2 1.9f – – –  clindamycin ≤0.25 >2 77.6 0.2 22.2 77.8 – 22.2  erythromycin 0.03 >32 67.3 0.3 32.5 67.3 0.3 32.5  levofloxacin 1 2 98.1 0.4 1.6 98.1 – 1.9  penicillin 0.03 2 65.9 18.5 15.6g 65.9 – 34.1e 65.9 – 34.1h 65.9 25.1 9.0f 91.0 7.9 1.1i – – –  piperacillin/tazobactam ≤0.06 4 – – – – – –  tetracycline ≤0.25 >8 69.3 0.3 30.5 69.3 0.3 30.5  tigecycline 0.03 0.06 99.2 – – – – –  trimethoprim/sulfamethoxazole 0.25 >4 68.8 11.4 19.7 76.3 4.0 19.7  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 VGS (469)  linezolid 1 1 99.6 – – – – –  amoxicillin/clavulanic acid 0.06 2 – – – 81.0 12.2 6.8  ceftriaxone 0.12 1 91.3 3.0 5.8 87.2 – 12.8  clindamycin ≤0.25 >2 86.1 0.9 13.0 87.0 – 13.0  daptomycin 0.25 0.5 100.0 – – – – –  erythromycin 0.03 >32 56.5 0.9 42.6 – – –  levofloxacin 1 2 94.2 1.1 4.7 – – –  penicillin 0.06 1 73.6 19.6 6.8 81.0 12.2 6.8  piperacillin/tazobactam 0.25 4 – – – 81.0 12.2 6.8  teicoplanin 0.12 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 65.7 2.3 32.0 – – –  tigecycline 0.03 0.06 100.0 – – – – –  trimethoprim/sulfamethoxazole ≤0.12 4 – – – – – –  vancomycin 0.5 0.5 100.0 – – 100.0 – 0.0 BHS (736)  linezolid 1 1 100.0 – – 100.0 0.0 0.0  amoxicillin/clavulanic acid ≤0.03 0.06 99.6 – – 99.9 – 0.1  ceftriaxone 0.03 0.06 100.0 – – 99.9 – 0.1  clindamycin ≤0.25 >2 87.9 0.7 11.4 88.6 – 11.4  daptomycin ≤0.06 0.25 100.0 – – 100.0 – 0.0  erythromycin 0.03 >32 77.7 1.8 20.6 77.7 1.8 20.6  levofloxacin 0.5 1 95.9 0.8 3.3 95.9 – 4.1  penicillin 0.015 0.06 99.6 – – 99.9 – 0.1  piperacillin/tazobactam 0.12 0.25 – – – 99.9 – 0.1  teicoplanin 0.25 0.25 – – – 100.0 – 0.0  tetracycline 0.5 >8 52.0 2.7 45.3 51.3 0.7 48.0  tigecycline 0.06 0.06 100.0 – – 100.0 0.0 0.0  trimethoprim/sulfamethoxazole ≤0.12 0.25 – – – – – –  vancomycin 0.25 0.5 100.0 – – 100.0 – 0.0 a VGS, viridans group streptococci; BHS, β-haemolytic streptococci. b Criteria as published by CLSI10 and EUCAST,12 except for tigecycline under the CLSI column (FDA). ‘–’ indicates absence of interpretive breakpoint criteria. S, susceptible; I, intermediate; R, resistant. c Susceptibility based on oxacillin results. d Results based on breakpoints for urinary tract infections only. e Using meningitis breakpoints. f Using non-meningitis breakpoints. g Using oral breakpoints. h Using parenteral, meningitis breakpoints. i Using parenteral, non-meningitis breakpoints. Comparative analysis showed that linezolid, daptomycin, tigecycline and the glycopeptides were active against MRSA (96.7%–100.0% susceptible) when applying current clinical breakpoints (Table 3). Similar susceptibility results (92.0%–100.0% susceptible) were observed against the entire CoNS collection. Overall, high susceptibility rates (98.5%–100.0% susceptible) were noted for all drugs tested against the E. faecalis collection, except for erythromycin (intrinsically resistant)14 and levofloxacin (for urinary tract infections only).10,12 In contrast, E. faecium exhibited an acceptable (>90.0%) susceptibility rate for linezolid, daptomycin and tigecycline. This species showed a vancomycin non-susceptibility rate of 29.8%. Overall, most agents tested against Streptococcus pneumoniae showed suboptimal coverage (<90.0% susceptible), except for linezolid, amoxicillin/clavulanate, levofloxacin, tigecycline and vancomycin (Table 3). Penicillin and ceftriaxone were active (91.0%–92.9% susceptible) when parenteral breakpoints were applied. The penicillin non-susceptibility rates (penicillin MICs of ≥ 0.12 mg/L) for S. pneumoniae were: Asia-Pacific (APAC) (47.8%) followed by Latin America (36.3%), Europe (29.6%) and Canada (20.0%) (data not shown). Non-susceptibility rates for ceftriaxone (EUCAST breakpoint) were highest in the APAC region (27.8%), with rates of 12.8%–15.6% in the other areas (data not shown). S. pneumoniae displaying non-susceptibility to levofloxacin were only observed in the APAC region (4.1%) and Europe (1.7%). Linezolid, ceftriaxone, daptomycin, levofloxacin, teicoplanin, tigecycline and vancomycin were active against viridans-group streptococci (91.3%–100.0% susceptible) while linezolid, amoxicillin/clavulanate, ceftriaxone, the penicillins, the glycopeptides, daptomycin, levofloxacin and tigecycline had coverage (95.9%–100.0% susceptible) against β-haemolytic streptococci (Table 3). Macrolide resistance was observed in 20.6% of β-haemolytic streptococcal isolates. The nations with macrolide resistance rates of ≥20% were as follows: Argentina (23.1%), Belgium (20.0%), Canada (25.0%), Croatia (20.0%), the Czech Republic (44.4%), Germany (20.0%), Guatemala (23.1%), Ireland (40.7%), Italy (42.4%), Japan (40.0%), Korea (28.6%), Portugal (25.0%), Russia (33.3%), Taiwan (64.3%) and the UK (23.1%). The vast majority (99.9%) of staphylococci were inhibited by linezolid at ≤2 mg/L and one Staphylococcus aureus isolate from Panama City showed a linezolid MIC of 4 mg/L, while four Staphylococcus epidermidis isolates had MIC values of 16–32 mg/L (Tables 2 and 4). The S. aureus isolate carried the cfr gene and belonged to ST72, whereas the four S. epidermidis isolates showed drug target alterations in several sites (Table 4). Multiple oxazolidinone target site alterations have become commonplace among CoNS in the last decade.1,3,S. epidermidis isolates that were non-susceptible to linezolid were mostly from Italy and belonged to ST2; this clonal type represents an important lineage that has been detected in several medical centres worldwide.15 A recent report described the dissemination of ST2 S. epidermidis isolates among Italian medical centres as well.16,17 Table 4. Isolates with elevated or non-susceptible linezolid MIC values (≥4 mg/L) observed during the ZAAPS programme (2016) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) a Typing results where relevant; PFGE performed among isolates from the same species recovered from the same centre; an S. epidermidis with an SEPI377A PFGE profile (ST2) was also detected in 2015 in this site; isolates with an EFM86A (ST117) PFGE profile were also observed in 2002, 2006, 2008 and 2009 in this site. Table 4. Isolates with elevated or non-susceptible linezolid MIC values (≥4 mg/L) observed during the ZAAPS programme (2016) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) Collection no. Organism City Country Linezolid Typinga MIC (mg/L) resistance mechanism(s) PFGE MLST 983392 S. aureus Panama City Panama 4 cfr ST72 948652 S. epidermidis Kiel Germany 16 23S rRNA (G2576T), L3(G137S, F147Y, M156T, H146P), L4 (71G72ins) ST2 978113 S. epidermidis Florence Italy 32 23S rRNA (G2576T), L3 (M156T), L4 (71G72ins) ST2 939504 S. epidermidis Genoa Italy 16 23S rRNA (G2576T) ST2 956526 S. epidermidis Milan Italy 16 23S rRNA (G2576T), L3 (M156T) SEPI377Aa ST2 973450 E. faecalis Paris France 4 optrA ST775 956335 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956343 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956349 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 956359 E. faecalis Guatemala City Guatemala 4 optrA EF361A ST256 986223 E. faecalis Durango Mexico 4 optrA EF126A ST480 986247 E. faecalis Durango Mexico 4 optrA EF126B ST480 981649 E. faecalis Taipei Taiwan 4 optrA ST766 954245 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 954473 E. faecium Rome Italy 8 23S rRNA (G2576T) EFM86Aa ST117 959706 S. gallolyticus Bangkok Thailand 4 optrA 939344 S. mitis group Ljubljana Slovenia 16 23S rRNA (G2576T) a Typing results where relevant; PFGE performed among isolates from the same species recovered from the same centre; an S. epidermidis with an SEPI377A PFGE profile (ST2) was also detected in 2015 in this site; isolates with an EFM86A (ST117) PFGE profile were also observed in 2002, 2006, 2008 and 2009 in this site. A total of eight E. faecalis from Guatemala City (4), Durango (2), Taipei (1) and Paris (1) were non-susceptible to linezolid (MICs of 4 mg/L) and all harboured optrA (Table 4). Isolates recovered from Guatemala City all had the same ST (ST256), as did the E. faecalis from Durango (ST480). Isolates associated with these STs were recovered previously from humans.18,19,E. faecalis isolates carrying optrA usually show genetic lineage diversity with occasional clonal dissemination within medical centres, as reported here and in previous studies.19,20 Only two E. faecium (Rome) isolates were linezolid resistant (MICs of 8 mg/L) and these isolates had 23S rRNA mutations (Table 4). These E. faecium were clonally related (ST117) and the PFGE profile demonstrated by these isolates was observed among linezolid-non-susceptible E. faecium isolates from this site on several occasions (Table 4). One S. gallolyticus (linezolid MIC of 4 mg/L) and 1 Streptococcus mitis (linezolid MIC of 16 mg/L) displayed elevated MIC results for linezolid. While the former carried optrA,13 the latter had 23S rRNA mutations (Table 4). Streptococcal isolates displaying non-susceptible MIC results for linezolid were rarely detected throughout the ZAAPS/LEADER programmes, with one Streptococcus oralis in 2002 (G2576T),21 one S. pneumoniae in 2010 (L4 mutation),22 one Streptococcus sanguinis from 2011 (23S rRNA mutations)23,24 and one S. sanguinis from 2013 (G2576T)25 detected during the programmes’ histories. Other streptococci demonstrating linezolid non-susceptibility were previously reported outside ZAAPS/LEADER,26–28 including the presence of cfr in a Streptococcus suis.28,29 The optrA gene was also previously detected in S. suis isolates recovered from pigs30 and this study reports the emergence of optrA in a S. gallolyticus causing human infection.13 These data show that linezolid has consistent potency against Gram-positive pathogens and emphasize the relevance of surveillance for detecting emerging resistance and for monitoring the evolution of resistance and associated pathogens. The final year of the ZAAPS programme (2016) reports the importance of optrA as an oxazolidinone resistance determinant with its emergence in S. gallolyticus and its dissemination and dominance as a resistance gene in E. faecalis. In previous studies, linezolid resistance among enterococci was mainly due to alterations in 23S rRNA, which remains the case for E. faecium.1 However, optrA has become more common in E. faecalis. This change can be explained, at least partially, by the lack of or a low fitness cost associated with the presence of optrA compared with the presence of mutations in general.31,32 It is interesting to note that cfr has also been associated with a generally low fitness cost in S. aureus,33 and the occurrence of cfr in S. aureus in this study (0.03%) was lower than the presence of optrA in E. faecalis (1.5%). A broader analysis shows that the prevalence of cfr in S. aureus during the last 3 years of LEADER (2013–15) and ZAAPS (2014–16) combined was 0.02% (5/20 349) but 62.5% (5/8) among isolates with linezolid MIC values of ≥4 mg/L.2,3,7 In a similar analysis, the occurrence of optrA in E. faecalis was 0.4% (14/3437) but 100.0% (14/14) in isolates with linezolid MIC values of ≥4 mg/L. cfr and optrA were initially detected in human specimens in these surveillance studies (ZAAPS/LEADER) in 20074 and 2006 (China; R. E. Mendes and L. Deshpande, unpublished data), respectively. These surveillance data suggest that optrA may be disseminating in E. faecalis more rapidly than cfr in S. aureus, implying a greater transferability of optrA.31 Surveillance and infection control will be important strategies to detect and contain the plasmid-mediated optrA resistance gene from disseminating. Acknowledgements We express appreciation to the following persons for technical support and/or manuscript assistance: S. J. R. Arends, L. R. Duncan, L. Flanigan, M. D. Huband, M. Janechek, J. Oberholser, T. Reynolds, P. R. Rhomberg, J. Schuchert, C. Smith and L. N. Woosley. Funding This study was sponsored by Pfizer Inc. Transparency declarations R. E. M., L. D., J. M. S., H. S. S., M. C. and R. K. F. are employees of JMI Laboratories, which received financial support from Pfizer in connection with the surveillance study and development of this manuscript via the SENTRY Antimicrobial Surveillance Program platform. JMI Laboratories also contracted to perform services in 2016–17 for Achaogen, Actelion, Allecra, Allergan, Ampliphi, API, Astellas, AstraZeneca, Basilea, Bayer, BD, Biomodels, Cardeas, CEM-102 Pharma, Cempra, Cidara, Cormedix, CSA Biotech, Cubist, Debiopharm, Dipexium, Duke, Durata, Entasis, Fortress, Fox Chase Chemical, GSK, Medpace, Melinta, Merck, Micurx, Motif, N8 Medical, Nabriva, Nexcida, Novartis, Paratek, Polyphor, Rempex, Scynexis, Shionogi, Spero Therapeutics, Symbal Therapeutics, Synolgoic, TGV Therapeutics, The Medicines Company, Theravance, ThermoFisher, Venatorx, Wockhardt and Zavante. There are no speakers’ bureaus or stock options to declare. P. A. H. is an employee of Pfizer Inc. References 1. Mendes RE , Deshpande LM , Jones RN. Linezolid update: stable in vitro activity following more than a decade of clinical use and summary of associated resistance mechanisms . Drug Resist Updat 2014 ; 17 : 1 – 12 . Google Scholar CrossRef Search ADS PubMed 2. 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Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: [email protected]. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Journal of Antimicrobial Chemotherapy – Oxford University Press

Published: Apr 6, 2018

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