This Petri dish culture plate contained a Mueller-Hinton agar growth medium that had been inoculated with a culture composed of Staphylococcus sp. bacteria. Atop the growth medium, antibiotic-impregnated disks had been laid, which gave rise to this example of an antibiotic sensitivity test. The medium was kept at a pH 8.0 on the left, and a pH 7.2 on the right.
The size of the inhibition zones (IZ) surrounding the antibiotic-impregnated paper disks depends on the sensitivity of the bacteria present in the agar, to the antibiotic, and the antibiotic's ability to diffuse through the culture medium. In this case, the results were as follows:
- Tetracycline Disks (TE) produced an IZ of 18mm/22mm
- Lincomycin Disks (L) produced an IZ of 23mm/18mm
- Streptomycin Disks (S) produced an IZ of 23mm/20mm
- Erythromycin Disks (E) produced an IZ of 32mm/27mm.