Antibiotic disk susceptibility test

Acar JF, Goldstein FW. Disk susceptibility test. Lorian V, ed. Antibiotics in Laboratory Medicine, 3rd ed. Baltimore Williams and Wilkins, 1991 17-48. 

Bauer AW, Kirby MM, Sherris JC, et al. Antibiotic susceptibility testing by a standardized, single-disk method. Am J Clin Pathol 1966 45 ... 

A drag resistance test is used to determine the drag susceptibility of mycobacteria to different types of antibiotics. In this test, the collected specimen from the patient is cultivated on suitable media. Then paper disks of diameter 5 mm containing different kinds of antibiotics are placed on the media surface. After the incubation period (6—8 weeks), an inhibition zone appears around the colonies. By observing the diameters of the formed inhibition zones around each disk, we can know which antibiotic is the most effective to the bacterial population. 

Figure 1.1. Representation of a typical disk susceptibility assay. A paper disk impregnated with a suspected antibiotic compound is applied to an agar plate seeded with a test microorganism and the area of inhibited microbial growth is indicated by a cleared zone surrounding the disk.

TESTING FOR MICROBIAL SENSITIVITY TO ANTIMICROBIAL AGENTS Bacterial strains, even from the same species, may vary widely in sensitivity to antibiotics. Information about the antibiotic sensitivity of the infecting microorganism is important for appropriate drug selection. Various methods are used to assess susceptibility, including disk-diffusion, dilution test, and automated broth dilution. The results are either reported on a semi-quantitative scale i.e., resistant, intermediate, or susceptible) or in terms of the minimal inhibitory concentration (MIC). 

Antibiotic susceptibility and testing by a standardized single disk method. Am, J, Clin, Pathol, 45, 493-496. 

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