Antibiotic sensitivity

Antibiotic sensitivity or Antibiotic susceptibility is the susceptibility of bacteria to antibiotics, and it is used in clinical settings to aid in the selection of an appropriate antibiotic to treat a specific bacterial infection.

Overview

Antibiotic sensitivity testing (AST) is used to determine which antibiotic will be most successful in treating a bacterial infection in vivo. Testing for antibiotic sensitivity is often done by the disk diffusion method or broth dilution method. Both methods require the isolation of a bacterial sample, which is then exposed to various antibiotics. If an antibiotic prevents the bacteria from growing, the bacteria are considered sensitive to that antibiotic.

Disk Diffusion Method

In the disk diffusion method, a bacterial sample is spread over the surface of a agar medium. Paper disks, each impregnated with a specific concentration of an antibiotic, are placed on the surface of the agar. The antibiotic diffuses from the disk into the agar. This creates a gradient of antibiotic concentration in the agar. If the bacteria are sensitive to the antibiotic, a clear ring, or zone of inhibition, is seen around the disk where the concentration of the antibiotic is high enough to prevent bacterial growth.

Broth Dilution Method

In the broth dilution method, a series of tubes containing equal volumes of a nutrient broth are inoculated with a standard amount of the test organism. To each tube in the series, a different concentration of antibiotic is added. The tubes are then incubated. After incubation, each tube is examined for bacterial growth. The lowest concentration of antibiotic that prevents bacterial growth is the minimum inhibitory concentration (MIC).

Clinical Significance

Antibiotic sensitivity testing is crucial in clinical settings to determine the susceptibility of bacteria to various antibiotics. This information can guide the selection of an appropriate antibiotic to treat the infection. It is particularly important in the treatment of serious infections and in situations where the responsible bacteria are likely to be resistant to commonly used antibiotics.

See Also

• Antibiotic resistance
• Pharmacology
• Microbiology

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Antibiotic sensitivity Resources
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