Tests to Guide Chemotherapy

The Kirby-Bauer disk-diffusion method is a test that uses antibiotic impregnated circular wafers to test whether or not bacteria is succeptible to a given drug. Bacteria is grown on a plate of agar and the circular wafers are placed throughout the plate. After an incubation period one can see a clear area around the circles. This is known as the zone of inhibition. The diameter of the zone and the rate of diffusion of the antibiotic are used to measure the efficacy of the drug. This helps in determining which antibiotic to use for a given infection. Broth dilution tests can also be used to determine the strength of an antibiotic. In this test an antibiotic is diluted several times in test tubes and each tube is inocculated with bacteria. After incubation they are analyzed for turbidity. The minimum inhibitory concentration or MIC of tghe drug is defined as the lowest concentration that prevents growth. The lethal concentration that actually kills the bacteria is called the minimum bactericidal concentration or MBC. Caltech Industries, Kimberly Clark, and Polyscience Corporation make products used in microbiology labs worldwide.