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Zone of Inhibition Test for Antimicrobial Activity

The assay pictured below is a Zone of Inhibition Test, also called a Kirby-Bauer Test. It is used clinically to measure antibiotic resistance and industrially to test the ability of solids and textiles to inhibit microbial growth.

Brief Summary: About a million cells from a single strain are spread over the agar plate using a swab, then incubated in the presence of the antimicrobial object (in this case a methicillin disk). If the bacterial or fungal strain is susceptible to the antimicrobial agent, then a zone of inhibition appears on the agar plate, such as on the agar plate on the left-hand side of the photo below. If it is resistant to the antimicrobial agent, then no zone is evident.

Photograph: A zone of Inhibition is evident around the oxacillin disk for S. aureus, left, but not for Methicillin-resistant S. aureus (MRSA), right.

Researchers who develop antimicrobial textiles, surfaces, and liquids use this test as a quick and easy way to measure and compare levels of inhibitory activity. If you work for a company that is interested in measuring the antimicrobial activity of a product, contact us to get started.

Below, we provide a summary of the Zone of Inhibition test method along with some of its strengths and weaknesses. The Zone of Inhibition test method is designed to qualitatively test the ability of antimicrobial agents to inhibit the growth of microorganisms and takes 18-24 hours to complete.


Summary of the Zone of Inhibition Test:


Strengths of Zone of Inhibition Testing:


Weaknesses of Zone of Inhibition Testing:


Zone of Inhibition Testing is a fast, qualitative means to measure the ability of an antimicrobial agent to inhibit the growth of microorganisms.

Antimicrobial Test Laboratories was built around antimicrobial innovation and antimicrobial research and development. If your company is interested in screening chemicals, products, or antimicrobial treatments for their ability to inhibit the growth of microorganisms, the zone of inhibition test may be a great place to start.

For more information about Zone of Inhibition testing, contact the Lab Today!