Performed to determine the susceptibility of the organism isolated from the diseased host; Generate antibiogram(s)
Broth Dilution MIC test
Agar Dilution MIC test
Broth/Agar MBC test
Agar Diffusion (Kirby-Bauer Disk) Test: Measure diameter of zone of inhibition; Read as susceptible, intermediate, or resistant
Factors influencing zones of inhibition on agar
Concentration of bacteria spread onto agar plate
Pathogen susceptibility
Antibiotic diffusion effects
Agar depth
Growth rate
Temperature
Nutrient availability
Drug antagonists
Factors influencing diffusion of antibiotic
Concentration of antibiotic: Kirby-Bauer disks, E-tests have standardized concentrations
Molecular weight of antibiotic
Water solubility of antibiotic
pH and ionization
Binding to agar
Modern Commercial Kits (e.g., E-test strips (up to six) on an agar plate and can be read out as MIC)
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