Disk diffusion antimicrobial susceptibility testing (Kirby-Bauer procedure)

The susceptibility of a bacterial isolate to antimicrobials is determined by measuring the diameter of the zone of growth inhibition (in millimeters) around each of the antibiotic-impregnated disks. The zone sizes are then classified as susceptible, intermediate, or resistant based on breakpoint tables published by the Clinical and Laboratory Standards Institute (CLSI), the European Committee on Antimicrobial Susceptibility Testing (EUCAST), or the United States Food and Drug Administration (FDA).