The inhibition zone test, also known as the agar diffusion test, is a method for testing the sensitivity of microorganisms to certain antibiotics or other diffusible inhibitors. Quantitative statements are not possible in this way.

Antimicrobial effectiveness

The aim of the study is to determine the antimicrobial efficacy of test specimens containing antimicrobial agents through the formation of inhibition zones (= microorganism-free zones).

The selected test organisms are representative of the organisms that can occur on the material. As standard, testing is carried out in triplicate per sample. The reference sample carried is tested in a single batch. The materials to be tested are placed on an agar culture medium homogeneously inoculated with test organisms and incubated in an incubator. The microorganism-free zone (inhibition zone) around the antimicrobial material provides information about its effectiveness.

The test method is suitable for testing the efficacy of highly diffuse antimicrobial agents. The agar diffusion test can be used to test the antimicrobial effect of textile materials such as surgical textiles, workwear for food processing companies or textile filters. A key functional criterion in the agar diffusion test is the contact of the sample with the agar and the microorganisms.


  • based on Pharm. 2.7.2.
  • DIN 58940-3
  • DIN EN 1104

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