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

Resistant

Answer

Intermediate

Answer

Non-susceptible

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

Greater resistance to the antibiotic

Answer

A bactericidal rather than bacteriostatic drug

Answer

Poor quality agar medium

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

It supports growth of fastidious organisms only

Answer

It contains antibiotics that enhance zone formation

Answer

It is the only agar that allows blood to be added for hemolysis detection

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

Target site modification

Answer

Efflux pump overexpression

Answer

Reduced outer membrane permeability

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

Resistant

Answer

Intermediate

Answer

Indeterminate

Question 6

What is the role of quality control strains such as Staphylococcus aureus ATCC 25923 in disk diffusion testing?

Accepted Answer

They verify that the testing conditions and reagents produce expected results

Answer

They serve as the test organism for each patient sample

Answer

They provide antibiotic disks for each test run

Answer

They are used to calculate patient MIC values

Question 7

Which antibiotic class is specifically tested using a cation-adjusted Mueller-Hinton broth to avoid falsely elevated MICs?

Accepted Answer

Aminoglycosides

Answer

Penicillins

Answer

Fluoroquinolones

Answer

Macrolides