scope:

This document describes the standard agar disk diffusion techniques used to determine the in vitro susceptibility of bacteria that grow aerobically. The document addresses preparation of agar plates, testing conditions (including inoculum preparation and standardization, incubation time, and incubation temperature), interpretation of results, quality control (QC) procedures, and limitations of disk diffusion methods. To assist the clinical laboratory, suggestions are provided on the selection of antimicrobial agents for routine testing and reporting. Standards for testing the in vitro susceptibility of bacteria that grow aerobically utilizing dilution methods are found in CLSI document M07²; standards for testing the in vitro susceptibility of bacteria that grow anaerobically found in CLSI document M11.³ Guidelines for standardized susceptibility testing of infrequently isolated or fastidious bacteria that are not included in CLSI document M02, M07, ² or M11³ are available in CLSI document M45.⁴