The purpose of the Kirby-Bauer disk diffusion susceptibility test is to determine the in vitro susceptibility of bacteria and fungi to various antimicrobial compounds. It is a standardized test that can be performed in a laboratory setting and is a valuable tool for both clinicians and microbiologists. The main benefits of this test are the flexibility of drug selection and obtaining overnight results. It is used to help guide the selection of antimicrobials for the appropriate treatment of infections caused by bacteria and fungi.
The test is performed by placing antimicrobial impregnated filter paper disks on the surface of an agar-containing medium that has been inoculated with the patient’s microorganism. Upon contact with the agar surface, the antimicrobial agent immediately diffuses from the disk into the surrounding agar where it may inhibit the growth of the microorganism. If the microorganism is inhibited by the antimicrobial agent, a clear zone of ‘no growth’ will be present around the paper disk after incubation. The presence or absence of a zone of inhibition around the disks is a measure of the microorganism’s susceptibility to the antimicrobial agent.
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The following procedure is performed in accordance with the 13th edition of the CLSI M02 document, “Performance Standards for Antimicrobial Disk Susceptibility Tests.” Refer to the current revision of the CLSI M100 document for the most updated recommendations, footnotes, and comments for testing conditions, reporting suggestions, and warnings. This procedure will cover an example of testing non-fastidious bacteria in the family, Enterobacterales, on standard Mueller Hinton Agar medium.
Please note that this tutorial is only intended as a guide, and is not a replacement for the instructions for use (IFU) for products referenced in this tutorial.
