Kirby-Bauer antibiotic testing



Kirby-Bauer, antibiotic testing (KB testing or disk diffusion antibiotic sensitivity testing) is a test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics. A known quantity of bacteria are grown on agar plates in the presence of thin wafers containing relevant antibiotics such as trimethoprim and nitrofurantoin, commonly used to tackle urinary tract infections. If the bacteria are susceptible to the antibiotics, an area of clearing surrounds the wafer where bacteria are not capable of growing (called a zone of inhibition). The size of the zone is correlated to the MIC or Minimum inhibitory concentration of antibiotic for that bacteria. In this way, health care providers are able to choose appropriate antibiotics to combat a particular infection.

Note: The Zone of Inhibition size is proportional to how sensitive the organism is to the particular antibiotic on the wafer; the rate of diffusion of the antibiotic in the medium also needs to be taken into account

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