$$\text{MBC} = \min \{ C : \text{no growth in subculture} \}$$

Question 1

Which of the following best explains why penicillin has little toxicity for human host cells?

Accepted Answer

Human cells lack peptidoglycan cell walls, which penicillin targets.

Question 2

A patient develops a superinfection after broad-spectrum antibiotic therapy. What is the most likely cause?

Accepted Answer

Destruction of normal microbiota, allowing opportunistic organisms to overgrow.

Question 3

Which mechanism of antibiotic resistance involves the modification of the drug’s target site?

Accepted Answer

Alteration of penicillin-binding proteins (PBPs) in MRSA.

Question 4

Which equation correctly represents the competitive inhibition of an enzyme by an antimetabolite?

Accepted Answer

$$E + I \rightleftharpoons EI$$

Question 5

A new antibiotic is found to bind the 30S ribosomal subunit of bacteria. Which class does it most likely belong to?

Accepted Answer

Aminoglycosides

Question 6

Which of the following drugs is used to treat tapeworm infections by inhibiting ATP production?

Accepted Answer

Niclosamide

Question 7

Why are broad-spectrum antibiotics both advantageous and potentially problematic?

Accepted Answer

They efficiently target many bacteria but can destroy normal microbiota, leading to superinfections.

Question 8

Which test is used to determine the minimal inhibitory concentration (MIC) of an antibiotic?

Accepted Answer

Broth dilution test

Question 9

A patient’s urine turns orange-red after starting tuberculosis treatment. Which drug is most likely responsible?

Accepted Answer

Rifampin

Question 10

Which of the following is a mechanism by which bacteria can rapidly eject antibiotics from the cell?

Accepted Answer

Efflux pumps

Question 11

Which antifungal drug acts by binding to ergosterol and disrupting fungal cell membrane permeability?

Accepted Answer

Amphotericin B

Question 12

Which of the following best describes the action of sulfonamides?

Accepted Answer

They competitively inhibit the synthesis of folic acid by resembling PABA.

Question 13

Which equation represents the calculation of the minimal bactericidal concentration (MBC) in a broth dilution test?

Accepted Answer

$$	ext{MBC} = \min \{ C : 	ext{no growth in subculture} \}$$

Question 14

Which of the following is a reason why it is easier to develop drugs against prokaryotic cells than eukaryotic pathogens?

Accepted Answer

Prokaryotic cells have unique structures like peptidoglycan cell walls not found in human cells.

Question 15

Which of the following drugs is used to treat malaria by targeting Plasmodium in both asexual and sexual stages?

Accepted Answer

Chloroquine

Question 16

Which mechanism of action is shared by quinolones and fluoroquinolones?

Accepted Answer

Inhibition of DNA gyrase, preventing DNA replication.

Question 17

Which of the following best describes the concept of selective toxicity?

Accepted Answer

A drug kills harmful microbes without damaging the host.

Question 18

Which combination of drugs demonstrates synergism in treating bacterial infections?

Accepted Answer

Trimethoprim and sulfamethoxazole

Question 19

Which of the following is a common mechanism by which resistance genes are transferred between bacteria?

Accepted Answer

Plasmids and transposons

Question 20

Which antiviral drug acts as a nucleoside analog to inhibit HIV replication?

Accepted Answer

Zidovudine

Week 5a: Antimicrobial Drugs – Mechanisms, Spectrum, and Resistance

Study Guide - Practice Questions