How does the concentration of antibiotics varies within the zone of inhibition formed in disk diffusion test?
The correct answer and explanation is:
In a disk diffusion test, the concentration of antibiotics varies across the zone of inhibition in a gradient pattern. At the center of the disk, where the antibiotic is initially placed, the concentration is highest. As the antibiotic diffuses outward from the disk, the concentration decreases gradually, creating a circular zone of inhibition. This zone represents an area where the bacteria cannot grow due to the antimicrobial activity of the antibiotic.
The size of the zone of inhibition is inversely related to the concentration of the antibiotic in the surrounding agar. High concentrations at the center cause complete bacterial inhibition, and as the concentration decreases with distance from the disk, the ability of the antibiotic to inhibit bacterial growth diminishes. The edge of the zone marks the point where the antibiotic concentration is no longer effective at preventing bacterial growth.
In the context of the test, the diameter of the zone of inhibition is measured and used to assess the susceptibility of the bacteria to the antibiotic. The larger the zone, the more susceptible the bacteria are to the antibiotic, indicating a higher effectiveness of the antibiotic at inhibiting bacterial growth. Smaller zones suggest reduced susceptibility, potentially due to a lower concentration of the antibiotic or the presence of resistant bacteria.
Factors such as the antibiotic’s diffusion rate, molecular size, and the agar’s thickness and composition also influence how the antibiotic spreads and, consequently, the size of the inhibition zone. This pattern of antibiotic concentration and bacterial growth provides valuable information about the efficacy of different antibiotics against specific bacterial strains.