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In this article we will discuss about the Antibiotic Sensitivity Test of Bacteria.
Subcultures of the test organisms are made in broth and incubated for 6-18 hours. Any density of inoculum may be used but in most cases the surfaces of cultures plates may be sown with broth containing approximately 100 million cells per ml.
After drying the surface, the previously prepared disks of filter paper saturated with various concentrations of antibiotics are applied, the plates are incubated, and the zone of inhibition is measured.
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A zone of inhibition of growth around the disk may indicate that the antimicrobial agent is either bactericidal (S = bacteria are sensitive) or merely bacteriostatic (RR = bacteria are relatively resistant) or bacteria are resistant (R = resistant). If the test organism is not resistant to the antibiotic, zones of complete inhibition of the growing organism are found around the disks containing the effective antibiotic (Fig. 7.2).
Culture and sensitivity test report of diagnostic microbiological laboratory.
Culture-organism isolated. Staphylococcus aureus.
Sensitivity : Penicillin — R
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Tetracycline — S
Gentamycin — S
Streptomycin — RR
(R = resistant; S = sensitive; RR = relatively resistant)
