|Description:||This 1972 image depicted two Mueller-Hinton agar culture plates that had been used in an antibiotic susceptibility test (AST). Known as the Kirby-Bauer method, each of the small labeled discs, or wafers, contained an antibiotic cocktail. The light halos surrounding each disc, also known as “reaction zones”, represented regions in which the bacteria on the agar’s surface did not thrive, due to their sensitivity to the antibiotic that had been soaked into these respective discs.|
These tests which measure the presence or absence of a reaction zone, also take into account the pH of the medium, the concentration of the inoculum, i.e., bacteria, and a number of other factors. Using this method, the sensitivity of a bacterial strain to a given antibiotic, or combination of antibiotics, i.e., antimicrobials, may be determined.