How to Measure Zones of Inhibition or ZOI – Microbiology Resources

Open education resourcesBiomedical ScienceMicrobiology

Microbiology resources


Image: “Zone of Inhibition” animated resource.
Creative Commons BY SA.

Content Authors:                                                Level:

Marilena Ioannou and Malgorzata Rekas                       General interest

OER Features:

 Click here for: Animation of measuring ZOI

Click here for: Video of measuring ZOI on YouTube

Microbiology OER Description:

These OERs are microbiology resources explaining the fundamental principle of how to measure zones of inhibition or ZOI. This is a simple microbiology screening test to assess the effect of antibacterial agents on bacterial growth. Bugs are grown on agar plates and a round disc containing a known concentration of antibiotic is placed. If the bacteria is susceptible to the antibiotic, then there will be an area where it does not grow.

In an experimental situation, measuring the dimensions of the zone of inhibited growth can help compare the effects of different antibiotics and different concentrations.


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