Question 1

Which of the following best describes the principle of selective toxicity in antimicrobial therapy?

Accepted Answer

The drug selectively inhibits or destroys pathogens without harming host cells.

Question 2

Why are antibiotics that target peptidoglycan synthesis generally more effective against Gram-positive bacteria than Gram-negative bacteria?

Accepted Answer

Gram-positive bacteria have a thicker peptidoglycan layer and lack an outer membrane, making them more accessible to antibiotics.

Question 3

A patient is prescribed a broad-spectrum antibiotic. Which of the following is a potential negative consequence of this treatment?

Accepted Answer

It may disrupt normal microbiota, leading to overgrowth of opportunistic organisms such as yeast.

Question 4

Which of the following best explains why sulfa drugs (sulfonamides) selectively inhibit bacterial cells but not human cells?

Accepted Answer

Humans obtain folic acid from their diet, while bacteria must synthesize it from PABA.

Question 5

Which of the following is the primary mechanism by which β-lactam antibiotics, such as penicillin, inhibit bacterial growth?

Accepted Answer

Blocking transpeptidation, preventing cross-linking of peptidoglycan in the cell wall.

Question 6

A laboratory is testing a new antibiotic using the broth dilution method. The minimum inhibitory concentration (MIC) is defined as:

Accepted Answer

The lowest concentration of antibiotic that prevents visible bacterial growth.

Question 7

Which of the following is a likely outcome if a patient is treated with an antibiotic that disrupts the plasma membrane of human cells?

Accepted Answer

Low selectivity and high toxicity, potentially damaging host tissues.

Question 8

Which of the following best describes the action of aminoglycoside antibiotics such as streptomycin?

Accepted Answer

They bind to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis.

Question 9

A patient develops a bacterial infection resistant to penicillin due to the production of β-lactamase. Which of the following best explains this resistance mechanism?

Accepted Answer

The bacteria produce an enzyme that hydrolyzes the β-lactam ring, inactivating the antibiotic.

Question 10

Which of the following is a reason why antibiotics that inhibit nucleic acid synthesis can be toxic to both bacteria and human cells?

Accepted Answer

DNA replication and transcription are highly conserved processes in both bacteria and humans.

Question 11

Which of the following best describes the synergistic effect observed when sulfonamides and trimethoprim are used together?

Accepted Answer

The combined drugs require a much lower dose to achieve the same effect as either drug alone.

Question 12

Which of the following is NOT a common mechanism by which bacteria develop resistance to antibiotics?

Accepted Answer

Increasing the rate of peptidoglycan synthesis.

Question 13

Acyclovir is an antiviral drug that structurally resembles deoxyguanosine. What is the primary mechanism by which acyclovir inhibits viral replication?

Accepted Answer

It acts as a nucleoside analog, terminating viral DNA synthesis.

Question 14

Which of the following best explains why penicillin does not affect mammalian cells?

Accepted Answer

Mammalian cells lack peptidoglycan cell walls, the target of penicillin.

Question 15

Which of the following is a major risk of using broad-spectrum antibiotics in a hospital setting?

Accepted Answer

They can lead to the development of antibiotic-resistant superinfections.

Question 16

Which of the following statements about the E-test for antibiotic susceptibility is correct?

Accepted Answer

It determines the minimum inhibitory concentration (MIC) of an antibiotic.

Question 17

Which of the following best describes the action of polymyxin B?

Accepted Answer

It disrupts the plasma membrane by binding to membrane phospholipids, increasing permeability.

Question 18

A patient is infected with a fungus. Which of the following drugs would most likely be prescribed?

Accepted Answer

Ketoconazole

Question 19

Which of the following is a reason why Gram-negative bacteria are less likely to produce antibiotics than Gram-positive bacteria?

Accepted Answer

Gram-negative bacteria have an outer membrane that limits the diffusion of antibiotics they produce.

Antimicrobial Drugs: Mechanisms, Spectrum, and Resistance

Study Guide - Practice Questions

Study Guide - Flashcards