Question 1

Which of the following best defines selective toxicity in the context of antimicrobial drugs?

Accepted Answer

The ability of a drug to target and kill only pathogenic microbes without harming host cells.

Question 2

Penicillin was the first widely used antibiotic. Which species is the natural source of penicillin, and to which kingdom does it belong?

Accepted Answer

Penicillium chrysogenum; Kingdom Fungi

Question 3

Which of the following best describes the difference between bactericidal and bacteriostatic drugs?

Accepted Answer

Bactericidal drugs kill bacteria, while bacteriostatic drugs inhibit bacterial growth.

Question 4

Which of the following is NOT one of the five major action modes of antibacterial drugs?

Accepted Answer

Inhibition of viral envelope formation

Question 5

Penicillinase is an enzyme that provides resistance to penicillin. What is its mechanism of action?

Accepted Answer

It hydrolyzes the beta-lactam ring of penicillin, rendering it inactive.

Question 6

Sulfonamides are a class of antimicrobial drugs. What is their primary mechanism of action?

Accepted Answer

They inhibit the synthesis of folic acid by acting as competitive inhibitors of para-aminobenzoic acid (PABA).

Question 7

The combination of trimethoprim and sulfamethoxazole (TMP-SMZ) is an example of drug synergism. Which of the following best describes drug synergism?

Accepted Answer

When two drugs together have a greater effect than the sum of their individual effects.

Question 8

Folic acid is essential for all cellular organisms. How do humans and bacteria obtain folic acid, respectively?

Accepted Answer

Humans obtain folic acid from their diet; bacteria synthesize it.

Question 9

Why is it more difficult to find a point of selective toxicity in antifungal drugs compared to antibacterial drugs?

Accepted Answer

Fungi are eukaryotic like human cells, so there are fewer unique targets that do not harm host cells.

Question 10

Acyclovir is an antiviral drug that stops viral replication. What nucleoside does it resemble, and how does it inhibit viral replication?

Accepted Answer

It resembles guanosine and acts as a chain terminator during viral DNA synthesis.

Question 11

Which of the following best explains why there are so few antiviral drugs compared to antibacterial drugs?

Accepted Answer

Viruses use host cell machinery for replication, making it difficult to target the virus without harming host cells.

Question 12

A hospital is testing the effectiveness of several antibiotics against a bacterial strain using the Kirby-Bauer test. What is measured in this test to determine antibiotic effectiveness?

Accepted Answer

The diameter of the zone of inhibition around antibiotic disks on an agar plate.

Question 13

Which of the following is NOT a common mechanism by which bacteria become resistant to antibiotics?

Accepted Answer

Increased uptake of the drug into the cell

Question 14

A patient is prescribed antibiotics for a bacterial infection but stops taking them after a few days when symptoms improve. Which of the following best explains how this misuse can lead to antibiotic resistance?

Accepted Answer

Stopping early allows the most resistant bacteria to survive and multiply.

Question 15

Which of the following scenarios best illustrates drug antagonism?

Accepted Answer

Two drugs are given together and their combined effect is less than the effect of either drug alone.

Question 16

A bacterial strain is found to be resistant to both penicillin and tetracycline. Which of the following is the most likely explanation for this multidrug resistance?

Accepted Answer

The bacterium has acquired a plasmid carrying multiple resistance genes.

Question 17

A patient is treated with a combination of two antibiotics, A and B. When used together, the minimum inhibitory concentration (MIC) of each drug is lower than when used alone. What does this indicate about the interaction between drugs A and B?

Accepted Answer

The drugs are synergistic.

Question 18

Which of the following equations best represents the concept of drug synergism, where the combined effect of two drugs (A and B) is greater than the sum of their individual effects?

Accepted Answer

$$E_{A+B} \u003e E_A + E_B$$

Question 19

A researcher is developing a new antibacterial drug that targets the synthesis of peptidoglycan. Which class of drugs does this mechanism most closely resemble?

Accepted Answer

Penicillins

Question 20

A patient with a fungal infection is prescribed an antifungal drug that targets ergosterol synthesis. Why is this drug less likely to harm human cells?

Accepted Answer

Human cells do not synthesize ergosterol; they synthesize cholesterol instead.

Microbiology Exam 5 Study Guide – Antimicrobial Drugs & Resistance

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