Microbial Susceptibility To Chemotherapeutic Agents

Species and strains may have the different degree to susceptibility towards antimicrobial agents. Moreover, microorganisms susceptibility may change even during the treatment. So, it become important for clinicians to check the susceptibility of particular microorganisms. This become important to keep the effectiveness of treatment. Here we would discuss about some methods by which we can check the susceptibility of microorganisms against chemotherapeutic agents.

Tube Dilution Technique

Susceptibility of a microorganisms against the antibiotics and other chemotherapeutic agents can be determined by tube dilution method or paper disk plate method. By working with tube dilution method, one can determined the smallest amount of chemotherapeutic agents required to inhibit the growth of the organism in vitro. This amount is referred to as MIC (minimal inhibitory concentration). To perform this test we need to go through following procedure:

Increasing amount of the antibiotics under examination are placed in a series of culture tubes containing the suitable broth media inoculated with the test organism. A starting tube (tube on the left) is made control i.e. having no antibiotics. The doses of drugs used in the test illustrated by the labels on the tube. After incubation, the concentration of drugs required to inhibit the growth of the organism used is determined by observing the absence of growth.

Disk Plate Technique

The paper disk plate method is the most commonly used technique for the determination of susceptibility of microorganisms to chemotherapeutic agents. Small paper disks are impregnated with known amounts of chemotherapeutic agent. And the disk is placed upon the surface of an inoculated plate. After incubation the plates are observed for the zone of inhibition (a clear area) around the disk. A zone of inhibition around the disk indicates that the organism was inhibited by the drug, which diffuse into the agar from the disk.