The compound or dressing under test (e.g. antibiotic) is placed onto an agar plate (either on disks or in wells or directly to the surface of the agar) seeded with a susceptible organism. As the drug/antimicrobial diffuses out through the agar, it inhibits the growth of the organism, producing a zone of inhibition. The zone can be measured and used in a variety of ways to gain information.
Can be used to asses the duration of longevity of dressings by means of transfer to fresh plates on each day.