Reproducibility of Control Strains for Antibiotic Susceptibility Testing

Reproducibility of Control Strains for Antibiotic Susceptibility Testing Marie B. Coyle * , Mary F. Lampe , Connie L. Aitken , Polly Feigl and John C. Sherris * Department of Immunology, Laboratory Medicine, and Biostatistics, School of Medicine, University of Washington, Seattle, Washington 98195 Department of Microbiology, Laboratory Medicine, and Biostatistics, School of Medicine, University of Washington, Seattle, Washington 98195 ABSTRACT Inter- and intralaboratory reproducibility of susceptibility testing requires stable control strains. The Food and Drug Administration diffusion procedure recommends the Seattle strains of Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) for this purpose. It was of interest to determine the present reproducibility of control cultures maintained in various laboratories over several years. Fifteen cultures each of S. aureus and E. coli were obtained from laboratories in different parts of the country. Their performance was compared with strains directly derived from ATCC. Diffusion susceptibility tests using a modified overlay technique were made with four replicates. Seven of the eight statistically significant differences in responses of the staphylococci were to penicillin, methicillin, or cephalothin. One culture was a penicillinase producer with a zone 15 mm less than the standard strain. Eleven of the 15 cultures showed no significant deviations or differences greater than 2 mm from the results with the strain derived directly from ATCC. All except the penicillinase producer were of identical phage type. Among 150 organism-antibiotic combinations tested with E. coli , all but one reading were within 2 mm of the standard. Four of the six statistically significant differences were in a culture from one laboratory. The stability of the cultures appears to have been influenced by the method of storage. Cultures that were kept frozen during extended storage were remarkably stable. Significant differences were found in cultures from four of five laboratories that maintained cultures in refrigerators or at ambient temperature. Copyright © 1976 American Society for Microbiology CiteULike Connotea Delicious Digg Facebook Google+ Mendeley Reddit StumbleUpon Twitter What's this? « Previous | Next Article » Table of Contents This Article doi: 10.1128/​AAC.10.3.436 Antimicrob. Agents Chemother. September 1976 vol. 10 no. 3 436-440 » Abstract PDF Classifications Physiological Effects and Microbial Susceptibility Services Email this article to a colleague Similar articles in ASM journals Alert me when this article is cited Alert me if a correction is posted Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of AAC Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Load citing article information Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Coyle, M. B. Articles by Sherris, J. C. Search for related content PubMed PubMed citation Articles by Coyle, M. B. Articles by Sherris, J. C. Related Content Load related web page information Social Bookmarking CiteULike Connotea Delicious Digg Facebook Google+ Mendeley Reddit StumbleUpon Twitter What's this? current issue December 2011, volume 55, issue 12 Alert me to new issues of AAC About AAC Subscribers Authors Reviewers Advertisers Inquiries from the Press Permissions & Commercial Reprints ASM Journals Public Access Policy AAC RSS Feeds 1752 N Street N.W. • Washington DC 20036 202.737.3600 • 202.942.9355 fax • [email protected] Print ISSN: 0066-4804 Online ISSN: 1098-6596 Copyright © 2011 by the American Society for Microbiology. For an alternate route to AAC .asm.org, visit: http://intl- AAC .asm.org | More Info»