- The Kirby-Bauer disk diffusion test is a standardized protocol for determining antibiotic susceptibility.
- A pure culture of the test organism is inoculated on Mueller-Hinton agar.
- Paper disks impregnated with a standardized concentration of individual antibiotics are added to the plate which is then incubated at 35 degrees Celsius. Results are read and interpreted at 18 hours of incubation.
- If the growth of a test organism is inhibited by the antibiotic on a disc, a zone of inhibition will appear. The zone of inhibition is a circular area surrounding an antibiotic disk in which the test organism does not grow.
- The diameter of the zone of inhibition is calibrated in millimeters and compared with the Interpretive Zone Standards published by the National Committee for Clinical Laboratory Standards.
- Results are reported:
as S (sensitive), I (intermediate), or R (resistant).
Antibiotic Sensitivity Test by Kirby-Bauer
