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Reliability of Disc Diffusion Susceptibility Testing

Published online by Cambridge University Press:  02 January 2015

Patrick R. Murray*
Affiliation:
Clinical Microbiology Laboratory, Departments of Pathology and Medicine, Barnes Hospital and the Washington University School of Medicine, St. Louis, MO
Jacquelyn R. Zeitinger
Affiliation:
Clinical Microbiology Laboratory, Departments of Pathology and Medicine, Barnes Hospital and the Washington University School of Medicine, St. Louis, MO
Donald J. Krogstad
Affiliation:
Clinical Microbiology Laboratory, Departments of Pathology and Medicine, Barnes Hospital and the Washington University School of Medicine, St. Louis, MO
*
Clinical Microbiology Laboratory, Barnes Hospital, St. Louis, MO 63110

Abstract

We retested 2,181 bacteria-antibiotic combinations with the Kirby-Bauer disc-diffusion technique and found interpretive changes with 120 (5.5%). Most changes (101 of 120) were single steps (i.e. from R to I, I to R or S, or S to I). Of the 19 remaining, 10 of them were from R to Sand nine from S to R. These changes were significantly more frequent for combinations with zone diameters clustered near interpretive breakpoints (within 2mm) than for other combinations, and there was a linear relationship between decreased reproducibility and increased clustering near interpretive breakpoints.

Based on an analysis of all susceptibility testing results performed in 1978, combinations most commonly clustered near interpretive breakpoints included: Ampicillin with Klebsiella pneumoniae; erythromycin with enterococci; chloramphenicol with Serratia marcescens; gentamicin with Pseudomonas aeruginosa and enterocci; and tetracycline with Enterobacter spp., Escherichia coli, and K. pneumoniae.

Type
Original Articles
Copyright
Copyright © The Society for Healthcare Epidemiology of America 1982

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