Question 1

Which of the following best explains why penicillin is selectively toxic to bacteria but not to human cells?

Accepted Answer

Penicillin targets the synthesis of peptidoglycan, which is present in bacterial cell walls but absent in human cells.

Question 2

A patient is prescribed amphotericin B for a fungal infection. Which of the following best describes its mechanism of action?

Accepted Answer

It binds to ergosterol in fungal membranes, forming pores that disrupt membrane integrity.

Question 3

Sulfonamide antibiotics inhibit bacterial growth by interfering with which metabolic pathway?

Accepted Answer

Folic acid synthesis by acting as structural analogs of para-aminobenzoic acid (PABA)

Question 4

Which of the following is NOT a characteristic of an ideal antimicrobial drug?

Accepted Answer

It is expensive and difficult to administer.

Question 5

A broad-spectrum antibiotic is most likely to:

Accepted Answer

Act against a wide variety of pathogens, increasing the risk of secondary or superinfections.

Question 6

Which laboratory method is used to determine the minimum inhibitory concentration (MIC) of an antibiotic?

Accepted Answer

Serial dilution of antibiotic in broth followed by incubation with bacteria and observation of growth.

Question 7

A new bacterial strain is found to be resistant to penicillin due to the production of beta-lactamase. What is the most likely mechanism of resistance?

Accepted Answer

Enzymatic destruction of the antibiotic molecule.

Question 8

Which of the following best describes the E-test for antibiotic susceptibility?

Accepted Answer

A plastic strip with a gradient of antibiotic is placed on an inoculated agar plate, and the MIC is read where the elliptical zone of inhibition intersects the strip.

Question 9

Which of the following is a common consequence of using broad-spectrum antibiotics?

Accepted Answer

Development of secondary or superinfections due to disruption of normal microbiota.

Question 10

Which of the following is NOT a known mechanism by which bacteria can acquire resistance to antibiotics?

Accepted Answer

Increased sensitivity to the antibiotic.

Question 11

A patient is infected with a bacterial strain that has acquired an R-plasmid. Which process most likely led to this resistance?

Accepted Answer

Horizontal gene transfer via conjugation, transformation, or transduction.

Question 12

Why are humans not affected by sulfonamide antibiotics?

Accepted Answer

Humans obtain folic acid from their diet and do not synthesize it.

Question 13

Which of the following best explains why it is important to complete the full course of prescribed antibiotics?

Accepted Answer

To ensure all pathogenic bacteria, including those with partial resistance, are eliminated and to reduce the risk of developing resistance.

Question 14

Which of the following is a reason why pharmaceutical companies are reluctant to develop new antibiotics?

Accepted Answer

High development costs and low financial return due to limited use and rapid resistance development.

Question 15

A bacterial population is exposed to an antibiotic. After treatment, only a few cells survive and multiply. What is the most likely explanation for this observation?

Accepted Answer

The surviving cells possessed resistance genes, either through mutation or horizontal gene transfer.

Question 16

Which of the following is a strategy to limit the development of antibiotic resistance in clinical settings?

Accepted Answer

Using antibiotics only when absolutely necessary and in combination when appropriate.

Question 17

Which of the following best describes the action of aminoglycoside antibiotics?

Accepted Answer

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

Question 18

A patient develops a secondary infection after antibiotic treatment. Which of the following best explains this phenomenon?

Accepted Answer

The antibiotic disrupted the normal microbiota, allowing opportunistic pathogens to proliferate.

Question 19

Which of the following equations correctly represents the calculation of the minimum inhibitory concentration (MIC) in a serial dilution test?

Accepted Answer

$$MIC = 	ext{lowest concentration of antibiotic (\mu g/mL) that inhibits visible growth}$$

Question 20

Which of the following is an example of cross-resistance?

Accepted Answer

A bacterium that is resistant to multiple drugs due to a single resistance mechanism, such as an efflux pump.

Controlling Microbial Growth in the Body: Antimicrobial Drugs and Resistance

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