Zone of inhibition

Where enough of it prevents bacterial growth, a clear zone of inhibition appears around the disc. Comparing these zones lets you investigate how different treatments affect the bacteria on the plate.

If it prevents bacteria growing nearby, a clear zone of inhibition appears against the surrounding bacterial growth. The disc and its clear zone make the effect visible and measurable.

Where an agent prevents visible growth, a clear zone of inhibition appears around its disc.

If it prevents growth, a clear zone of inhibition appears around the disc. A wider zone suggests greater effectiveness against the bacteria tested under those conditions; it does not, by itself, show that the bacteria were killed.