Most commonly used method for testing antibiotic susceptibility of bacteria-

Ans. is 'a' i.e., Kirby-Bauer disc diffusion method Antibiotic sensitivity testingo Antibiotic sensitivity testing is carried out to determine appropriate antibiotic to be used for a particular strain isolated from clinical specimens, o Antibiotic testing can be carried out by two broad methods :a) Disc diffusion testsb) Dilution testsA) Disc diffusion tests# There are most commonly used methods to determine antibiotic susceptibility.# Discs impregnated with known concentration of antibiotics and are placed on the culture medium that has been inoculated with a culture of bacterium to be tested.# Antibiotic sensitivity is determined by zone of inhibition of bacterial growth around the disc.Selection of media# Medium that supports both test and control strains is selected for carrying out antibiotic susceptibility testing.# For example:i) Muller-Hinton agar is used for gram-negative bacilli and staphylococcus spp.ii) Blood agar is used for streptococcus spp and enterococcus spp.iii) Chocolate agar is used for Haemophilus influenzaeiv) Wellcotest medium uses antibiotics sulfonamide and cotrimoxazoleMueller -Hinton agar is most commonly used medium for antibiotic sensitivity testingType of disc diffusion test# Disc diffusion tests are following types:-i) Kirby-Bauer disc diffusion method - most commonly used.ii) Stoke disc diffusion methodiii) Primary disc diffusion testB) Dilution tests# These tests are used to determine minimum inhibitory concentration (MIC) of antibiotics.# Following methods are used to determine MICi) Broth dilution methodii) Agar dilution methodiii) Epsilometer test (E-test)