Question 1

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

Accepted Answer

The drug selectively destroys pathogens without harming host cells.

Question 2

Paul Ehrlich and Alexander Fleming made significant contributions to chemotherapy. Which of the following pairs correctly matches each scientist with their discovery?

Accepted Answer

Ehrlich: developed the concept of selective toxicity; Fleming: discovered penicillin

Question 3

Which group of microorganisms is the primary source of most clinically useful antibiotics?

Accepted Answer

Actinomycetes, especially Streptomyces species

Question 4

A patient develops a superinfection after broad-spectrum antibiotic therapy. What is the most likely explanation for this phenomenon?

Accepted Answer

The antibiotic promoted the overgrowth of resistant normal microbiota.

Question 5

Which of the following best explains why it is more difficult to develop chemotherapeutic agents against viruses than against bacteria?

Accepted Answer

Viruses use the host's cellular machinery for replication, making selective toxicity challenging.

Question 6

Which of the following drugs inhibits bacterial cell wall synthesis by preventing the cross-linking of peptidoglycans?

Accepted Answer

Penicillin

Question 7

Aminoglycosides, such as streptomycin, exert their antibacterial effect by which of the following mechanisms?

Accepted Answer

Changing the shape of the 30S subunit of the 70S ribosome

Question 8

A patient is prescribed a combination of trimethoprim and sulfamethoxazole (TMP-SMZ) for a urinary tract infection. What is the main advantage of using this combination?

Accepted Answer

The combination exhibits drug synergism, increasing efficacy.

Question 9

Which of the following best describes the mechanism of action of chloramphenicol?

Accepted Answer

It binds to the 50S subunit of the 70S ribosome and inhibits peptide bond formation.

Question 10

A hospital antibiogram shows increasing resistance to ciprofloxacin in E. coli isolates over the past year. Which of the following is the most likely explanation for this trend?

Accepted Answer

Horizontal gene transfer of resistance genes among bacteria

Question 11

Which of the following statements about the disk-diffusion (Kirby-Bauer) method is correct?

Accepted Answer

It determines the sensitivity of an organism to an antibiotic by measuring the zone of inhibition.

Question 12

Which of the following equations correctly represents the action of penicillinase on penicillin?

Accepted Answer

$$\mathrm{Penicillin} \xrightarrow{\mathrm{penicillinase}} \mathrm{Penicilloic\ acid}$$

Question 13

Which of the following is a major side effect associated with the use of amphotericin B?

Accepted Answer

Kidney toxicity

Question 14

A patient with a tapeworm infection is treated with niclosamide. What is the primary mechanism of action of this drug?

Accepted Answer

Prevents ATP production in the parasite

Question 15

Which of the following best explains why sulfonamides are effective antibacterial agents?

Accepted Answer

They competitively inhibit the enzyme that converts PABA to folic acid.

Question 16

A patient is prescribed erythromycin for a gram-positive bacterial infection. Which structural feature is characteristic of macrolide antibiotics like erythromycin?

Accepted Answer

A macrocyclic lactone ring

Question 17

Which of the following best describes the mechanism of resistance involving rapid efflux in bacteria?

Accepted Answer

Bacteria pump the antibiotic out of the cell before it can act.

Question 18

A patient with a systemic fungal infection is treated with a triazole. What is the primary target of this class of antifungal drugs?

Accepted Answer

Inhibition of ergosterol synthesis in the fungal membrane

Question 19

Which of the following statements about the therapeutic index is correct?

Accepted Answer

A high therapeutic index indicates a greater margin of safety for the drug.

Chapter 20: Antimicrobial Drugs – Microbiology Study Notes

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