Zone of Clearance/ Inhibition (ZOC/ZOI)
Duration – 48 hours
Lead time – 14 days
Standard Results – Microbiology
MODEL UTILITY:
This in vitro antimicrobial assay is typically used as an initial screening to determine possible antimicrobial activity of novel materials which can be liquids or solids. This assay can quantify the potential antimicrobial potency of the test material(s) relative to various controls.
HOW THE MODEL WORKS:
In this assay an agar plate is evenly coated with an inoculation “lawn” of the challenge microbe. Then, a circular plug is removed from the center of the plate and the resulting well is filled with a known amount of the test material. Alternatively, a sterile disk coated with the test material is placed in the center of the plate. The agar plates are incubated overnight. For materials with anti-microbial properties, a ring of no-growth will be present around the well. The area of the ring is measured and that area can be used to compare different test materials.
EXAMPLE DATA:
This data is from a study comparing 5 novel topical antimicrobial materials to a predicate material positive control and a sham negative control. The corrected zone of inhibition is the area of the well the material is placed in subtracted from the area of no-growth.
Figure 1. A comparison of the area of the corrected zone of inhibition of 5 novel antimicrobial materials compared to a predicate material positive control and a sham negative control.
Figure 2. Examples of the zone of inhibition for three different treatments. (A) Saline treated negative control, no zone of inhibition present; (B) A predicate treated positive control, large zone of inhibition present; (C) test material treated plate, small zone of inhibition present.
Advantages:
This model is inexpensive and allows for high throughput screening of novel materials.
Disadvantages:
This in vitro model does not consistently predict anti-microbial activity when the material is used in an in vivo model, as is common with many in vitro tests.