AP-Micro Microbiology: Antimicrobial Susceptibility Testing 2

Question 1

Which CLSI breakpoint category indicates that an organism is inhibited by drug concentrations achievable with standard dosing?

Accepted Answer

Susceptible

Answer

The 'Susceptible' category means the organism is inhibited at drug levels achievable with standard dosing regimens.

Question 2

In the Kirby-Bauer disk diffusion method, what does a larger zone of inhibition indicate?

Accepted Answer

Greater susceptibility to the antibiotic

Answer

A larger zone of inhibition indicates that the organism is more susceptible because fewer bacteria survive at greater distances from the drug-laden disk.

Question 3

What is the purpose of using Mueller-Hinton agar specifically for disk diffusion susceptibility testing?

Accepted Answer

It has low thymidine content and supports reproducible results for most pathogens

Answer

Mueller-Hinton agar is recommended because its low thymidine content avoids interference with sulfonamide and trimethoprim testing and gives reproducible results.

Question 4

Which mechanism of resistance involves a bacterium producing an enzyme that destroys an antibiotic before it can act?

Accepted Answer

Enzymatic inactivation

Answer

Enzymatic inactivation, such as beta-lactamase production, destroys the antibiotic molecule before it reaches its target.

Question 5

A laboratory reports an MIC of 0.25 µg/mL for an antibiotic with a susceptible breakpoint of ≤0.5 µg/mL. How should this result be interpreted?

Accepted Answer

Susceptible

Answer

Because the MIC (0.25 µg/mL) is at or below the susceptible breakpoint (≤0.5 µg/mL), the organism is classified as susceptible.

AP Practice Test

AP Practice Test

AP-Micro Microbiology: Antimicrobial Susceptibility Testing 2