Molecular Microbiology

doi: 10.1111/mmi.14023pmid: N/A

Vázquez‐Boland, José A.; Meijer, Wim G.

doi: 10.1111/mmi.14267pmid: 31099908

Rhodococcus equi is the only recognized animal pathogenic species within an extended genus of metabolically versatile Actinobacteria of considerable biotechnological interest. Best known as a horse pathogen, R. equi is commonly isolated from other animal species, particularly pigs and ruminants, and causes severe opportunistic infections in people. As typical in the rhodococci, R. equi niche specialization is extrachromosomally determined, via a conjugative virulence plasmid that promotes intramacrophage survival. Progress in the molecular understanding of R. equi and its recent rise as a novel paradigm of multihost adaptation has been accompanied by an unusual nomenclatural instability, with a confusing succession of names: "Prescottia equi", "Prescotella equi", Corynebacterium hoagii and Rhodococcus hoagii. This article reviews current advances in the genomics, biology and virulence of this pathogenic actinobacterium with a unique mechanism of plasmid‐transferable animal host tropism. It also discusses the taxonomic and nomenclatural issues around R. equi in the light of recent phylogenomic evidence that confirms its membership as a bona fide Rhodococcus.

Steenhuis, Maurice; Abdallah, Abdallah M.; de Munnik, Sabrina M.; Kuhne, Sebastiaan; Sterk, Geert‐Jan; van den Berg van Saparoea, Bart; Westerhausen, Sibel; Wagner, Samuel; van der Wel, Nicole N.; Wijtmans, Maikel; van Ulsen, Peter; Jong, Wouter S. P.; Luirink, Joen

doi: 10.1111/mmi.14255pmid: 30983025

Disarming pathogens by targeting virulence factors is a promising alternative to classic antibiotics. Many virulence factors in Gram‐negative bacteria are secreted via the autotransporter (AT) pathway, also known as Type 5 secretion. These factors are secreted with the assistance of two membrane‐based protein complexes: Sec and Bam. To identify inhibitors of the AT pathway, we used transcriptomics analysis to develop a fluorescence‐based high‐throughput assay that reports on the stress induced by the model AT hemoglobin protease (Hbp) when its secretion across the outer membrane is inhibited. Screening a library of 1600 fragments yielded the compound VUF15259 that provokes cell envelope stress and secretion inhibition of the ATs Hbp and Antigen‐43. VUF15259 also impairs β‐barrel folding activity of various outer membrane proteins. Furthermore, we found that mutants that are compromised in outer membrane protein biogenesis are more susceptible to VUF15259. Finally, VUF15259 induces the release of vesicles that appear to assemble in short chains. Taken together, VUF15259 is the first reported compound that inhibits AT secretion and our data are mostly consistent with VUF15259 interfering with the Bam‐complex as potential mode of action. The validation of the presented assay incites its use to screen larger compound libraries with drug‐like compounds.

Frirdich, Emilisa; Biboy, Jacob; Pryjma, Mark; Lee, Jooeun; Huynh, Steven; Parker, Craig T.; Girardin, Stephen E.; Vollmer, Waldemar; Gaynor, Erin C.

doi: 10.1111/mmi.14269pmid: 31070821

Campylobacter jejuni is a prevalent enteric pathogen that changes morphology from helical to coccoid under unfavorable conditions. Bacterial peptidoglycan maintains cell shape. As C. jejuni transformed from helical to coccoid, peptidoglycan dipeptides increased and tri‐ and tetrapeptides decreased. The DL‐carboxypeptidase Pgp1 important for C. jejuni helical morphology and putative N‐acetylmuramoyl‐L‐alanyl amidase AmiA were both involved in the coccoid transition. Mutants in pgp1 and amiA showed reduced coccoid formation, with ∆pgp1∆amiA producing minimal coccoids. Both ∆amiA and ∆amiA∆pgp1 lacked flagella and formed unseparated chains of cells consistent with a role for AmiA in cell separation. All strains accumulated peptidoglycan dipeptides over time, but only strains capable of becoming coccoid displayed tripeptide changes. C. jejuni helical shape and corresponding peptidoglycan structure are important for pathogenesis‐related attributes. Concomitantly, changing to a coccoid morphology resulted in differences in pathogenic properties; coccoid C. jejuni were non‐motile and non‐infectious, with minimal adherence and invasion of epithelial cells and an inability to stimulate IL‐8. Coccoid peptidoglycan exhibited reduced activation of innate immune receptors Nod1 and Nod2 versus helical peptidoglycan. C. jejuni also transitioned to coccoid within epithelial cells, so the inability of the immune system to detect coccoid C. jejuni may be significant in its pathogenesis.

Gore‐Lloyd, Deborah; Sumann, Inés; Brachmann, Alexander O.; Schneeberger, Kerstin; Ortiz‐Merino, Raúl A.; Moreno‐Beltrán, Mauro; Schläfli, Michael; Kirner, Pascal; Santos Kron, Amanda; Rueda‐Mejia, Maria Paula; Somerville, Vincent; Wolfe, Kenneth H.; Piel, Jörn; Ahrens, Christian H.; Henk, Daniel; Freimoser, Florian M.