M02-A8

Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved Standard-Eighth Edition

Susceptibility testing is indicated for any organism that contributes to an infectious process warranting antimicrobial chemotherapy, if its susceptibility cannot be reliably predicted from knowledge of the organism's identity. Susceptibility tests are most often indicated when the causative organism is thought to belong to a species capable of exhibiting resistance to commonly used antimicrobial agents. A variety of laboratory methods can be used to measure the in vitro susceptibility of bacteria to antimicrobial agents. In many clinical microbiology laboratories, an agar disk diffusion method is used routinely for testing common, rapidly growing, and certain fastidious bacterial pathogens. This document includes a series of procedures to standardize the way disk diffusion tests are performed. The performance, applications, and limitations of the current NCCLS-recommended methods are also described. The supplemental information (M100 tables) presented with this standard represents the most current information for drug selection, interpretation, and quality control using the procedures standardized in M2. These tables, as in previous years, have been updated and should replace tables published in earlier years. Changes in the tables since the most recent edition (M100-S12) appear in boldface type. Additionally, a glossary of antibiotic terms, classes, and abbreviations (for use with antimicrobial susceptibility testing disks and other in vitro test devices) has been added to the tables. It is anticipated that this glossary will provide an additional informational resource to users of the M2 standard, as it outlines antimicrobial terminology used in the susceptibility testing documents that may be unfamiliar or confusing to laboratory users. The glossary, as part of the M100 tabular information, will be continuously updated in future (yearly) revisions of M100.