1/26/2016 Disk-diffusion method for determining the The Diffusion Methods activity of antimicrobials. ·Disks containing antimicrobials are ·E test placed on a lawn of bacterial growth -Determines the minimal inhibitory ·Plates are incubated concentration (MIC) for a standardized time Lowest antibiotic concentration that Zone of inhibition is prevents visible bacterial growth e epe .A plastic coated strip contains a gradient of antibiotic concentrations sensitivity as The MIC is read from a scale printed on the -Sensitive strip -Intermediate -Resistant Etest(for epsilometer).a gradient diffusion method that determines antibiotic sensitivity and estimates Broth Dilution Tests minimal inhibitory concentration (MIC) Determine the MIC and minimal bactericidal concentration (MBC)of an antimicrobial drug Test organism is placed into the wells of a tray containing decreasing concentrations of a drug ·Growth is determined cedrg-rmdemeif red in drug-fre ermine if ·Antibiograms -Reports that record the susceptibility of organisms encountered clinically 10 1/26/2016 10 Disk-diffusion method for determining the activity of antimicrobials. • Disks containing antimicrobials are placed on a lawn of bacterial growth • Plates are incubated for a standardized time • Zone of inhibition is compared to a standard table that reports the sensitivity as ─ Sensitive ─ Intermediate ─ Resistant The Diffusion Methods • E test – Determines the minimal inhibitory concentration (MIC) • Lowest antibiotic concentration that prevents visible bacterial growth • A plastic coated strip contains a gradient of antibi i i ibiotic concentrations • The MIC is read from a scale printed on the strip E test (for epsilometer), a gradient diffusion method that determines antibiotic sensitivity and estimates minimal inhibitory concentration (MIC) MIC Broth Dilution Tests • Determine the MIC and minimal bactericidal concentration (MBC) of an antimicrobial drug • Test organism is placed into the wells of a tray containing decreasing concentrations of a drug • Growth is determined • The wells that do not show growth may be cultured in drug-free medium to determine if th d u is the drug is b ct icid l bactericidal or b ct i st tic bacteriostatic. • Antibiograms – Reports that record the susceptibility of organisms encountered clinically