Question 1

Which of the following best describes the principle behind the Kirby-Bauer disk diffusion test as shown in the image?

Accepted Answer

It assesses the susceptibility of bacteria to antibiotics by measuring zones of inhibition around antibiotic disks.

Question 2

In the image, the clear zones around the disks represent which of the following?

Accepted Answer

Zones of inhibition where bacterial growth has been prevented by the antibiotic.

Question 3

If the zone of inhibition around the IPM (imipenem) disk increases significantly when EDTA is present, what does this suggest about the bacterial isolate?

Accepted Answer

The bacteria produce a metallo-beta-lactamase enzyme that is inhibited by EDTA.

Question 4

Which of the following best explains why a standard table must be consulted when interpreting the results of a Kirby-Bauer test?

Accepted Answer

To compare the measured zone of inhibition to established breakpoints for susceptibility or resistance.

Question 5

Which of the following statements about antibiotic synergism is best illustrated by the image?

Accepted Answer

Synergism occurs when two antibiotics together produce a larger zone of inhibition than either alone.

Question 6

If a bacterial strain carries an R-plasmid, what is the most likely outcome when tested with multiple antibiotics using the Kirby-Bauer method?

Accepted Answer

The strain may show resistance to several antibiotics, resulting in small or no zones of inhibition.

Question 7

Which mechanism of resistance is most likely if a bacterium produces an enzyme that destroys the antibiotic before it can act?

Accepted Answer

Enzymatic degradation of the drug, such as by beta-lactamase.

Question 8

Why is it important to maintain a sufficient concentration of an antibiotic for a sufficient time during treatment?

Accepted Answer

To prevent the development of antibiotic resistance by ensuring all pathogens are inhibited or killed.

Question 9

Which of the following best describes the action of beta-lactam antibiotics such as penicillin?

Accepted Answer

They inhibit peptidoglycan synthesis by preventing cross-linkage of NAM subunits.

Question 10

A patient is treated with both sulfamethoxazole and trimethoprim for a urinary tract infection. This combination is an example of which of the following?

Accepted Answer

Antibiotic synergism.

Question 11

Which of the following is a reason why vancomycin is considered a narrow-spectrum antibiotic?

Accepted Answer

It is only effective against Gram-positive bacteria by blocking alanine-alanine linkages in peptidoglycan.

Question 12

Which of the following best explains why the use of broad-spectrum antibiotics can lead to secondary infections such as Clostridium difficile colitis?

Accepted Answer

They disrupt normal microbiota, allowing opportunistic pathogens to proliferate.

Question 13

Which of the following is the best definition of selective toxicity?

Accepted Answer

The ability of a drug to target pathogens without harming the host.

Question 14

Which of the following is a common mechanism by which bacteria acquire resistance genes from other bacteria?

Accepted Answer

Acquisition via transformation, transduction, or conjugation.

Study Guide: Controlling Microbial Growth in the Body – Antimicrobial Drugs (Chapter 10)

Study Guide - Practice Questions

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