ANTIMICROBIAL SUSCEPTIBILITY TESTING Flashcards
memorization
It is the least amount of antibiotic (highest dilution) that prevents visible growth.
Minimal Inhibitory Concentration (MIC)
Concentration of antibiotic that results in 99.9% decrease in CFU per mL
Minimal Bactericidal Concentration (MBC)
Kirby-Bauer disk diffusion test:
Principle: There is a/an ________ relationship the diameter of the zone of inhibited growth around the antibiotic disk and the logarithm of the ____________ of the antibiotic
There is an INVERSE LINEAR relationship;
the logarithm of the MINIMAL INHIBITORY CONCENTRATION
The lower the MIC, the ____ potency, and the ________ zone of inhibition
The lower the MIC, the higher potency, and the larger the zone of inhibition
Plate size used in Kirby-Bauer disk diffusion test:
150 x 15 mm plate
Agar used in KB disk diffusion test:
Mueller-Hinton Agar
pH of the medium should be:
7.2 to 7.4 pH
Agar depth should be held constant at:
4 mm (if in range: 4-6 mm)
The density of the inoculum should be adjusted to:
0.5 McFarland Standard
Equivalence of McFarland standard into CFU/mL
1.5 x 10^8 CFU/mL
if in range: 1-2 x 10^8 CFU/mL (Recall)
Preparation of McFarland Standard:
0.5 mL of 1.175% BaCl2 and
99.5 mL of 1% H2SO4
Too heavy inoculum results in:
Smaller zones/ False resistant
Too light inoculum results in:
Larger zones/ False susceptible
Only overnight colonies less than ____ hours should be test.
24 hours
Let inoculum dry at least ______ but not more than ______ before adding the disks.
at least 5 minutes but not more than 30 minutes