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Zone of Inhibition

Diffusion being measured on an agar plate at our Salt Lake City, UT location.

What is a Zone of Inhibition Test?

The Zone of Inhibition Test (also known as the Kirby-Bauer Test, Antimicrobial Susceptibility Test, Disk Diffusion Test, or the Agar Diffusion Test) is a quick and inexpensive way to assess the antimicrobial activity of a material or solution in relation to a target microorganism. Zone of Inhibition testing has been utilized for years and was first developed in the 1950’s and then standardized by the World Health Organization in 1961.

Typically, the Zone of Inhibition test is a qualitative test which is commonly used in the clinical setting to assess an antibiotic’s effect on a selected microorganism. As antimicrobial embedded products have entered the marketplace, the Zone of Inhibition test is now being used throughout the industry to assess the inhibitory nature against an array of different microorganisms. Its quick analysis allows for the screening of an antimicrobial product for inhibitory activity against a panel of different microorganisms. It is best performed if the antimicrobial can leach out of the material.

The Zone of Inhibition Test is a basic microbiological test commonly used throughout the medical device and pharmaceutical industries. Materials tested typically include leachable antimicrobial which has been embedded in plastics, textiles, solids, surfaces, liquids, gels, etc. as well as antibiotic solutions. Guidance for the susceptibility test from a clinical perspective may be found in:

  • CLSI Supplement M100 “Performance Standards for Antimicrobial Susceptibility Testing

Why is Zone of Inhibition Testing Important?

Testing for antimicrobial activity is expensive and time consuming, without considering the results of your test. Lost time can take away from a products speed to market. Which dictates how fast your product can get into consumer hands and whether you’re faster than your competition. Too much product delay allows other businesses to dominate the market, even with a substandard product. Associating your businesses as a follower instead of an industry leader.

This method of testing is simple and more affordable than expensive alternatives like broth dilution or the agar dilution method. Zone of Inhibition testing is a rapid way to determine the performance of a specific antimicrobial agent. Several samples can be tested for antimicrobial properties swiftly while results can be attainable in merely days.

Study Outline

At Nelson Labs, we provide technical expertise accompanied by proficiency in testing a vast catalog of products and bacterial assessments. Our customers can be certain that their Zone of Inhibition, Disk Diffusion Testing is executed accurately and knowledgeably.

In order to perform the Zone of Inhibition, Disk Diffusion Test, an agar plate is thoroughly spread with bacteria or fungal cells using a sterile swab. The antibiotic of choice is then infused into small paper filter discs. The antibiotic soaked filter discs are placed strategically on the agar plate and the whole plate is incubated for 18-24 hours. The results are visible immediately, with large “zones of inhibition” appearing around the discs indicating that the bacterial or fungal strain is susceptible to the antibiotic. If no “zone of inhibition” is present, then there is an indication for resistance against the antibiotic. The size of the diffusion between the filter discs and the cells usually refers to the level of antimicrobial activity present in the sample or product. The “zone of inhibition” is measured, documented, and interpreted by our scientists and the results are sent to you immediately.

Testing Locations

  • Salt Lake City, UT

To learn more about this location and its certifications, click here.

Contact Us

If you have additional questions about Zone of Inhibition testing services, or would like to consult with the experts at Nelson Labs, just send us a request or call us at +1 (801) 290-7500.