Q: Which equation is used to calculate the minimum inhibitory concentration (MIC) in a broth dilution test?

$$MIC = \text{lowest concentration of antibiotic that inhibits visible growth}$$

Question 1

Which of the following best explains why drugs that disrupt peptidoglycan synthesis are selectively toxic to bacteria but not to human cells?

Accepted Answer

Human cells lack peptidoglycan in their cell walls, so these drugs do not affect them.

Question 2

A patient is prescribed a drug that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. Which of the following is most likely the mechanism of action?

Accepted Answer

The drug prevents tRNA from binding to the ribosome, halting translation.

Question 3

Which of the following drugs acts by disrupting cytoplasmic membrane integrity, leading to cell lysis?

Accepted Answer

Polymyxins

Question 4

A new antibiotic inhibits the enzyme dihydrofolate reductase, which is essential for folic acid synthesis in bacteria. What is the most likely effect of this drug?

Accepted Answer

It prevents the synthesis of nucleic acids and proteins, inhibiting bacterial growth.

Question 5

Which of the following best describes the action of drugs that inhibit nucleic acid synthesis in bacteria?

Accepted Answer

They interfere with DNA or RNA replication and transcription, preventing cell division.

Question 6

A physician orders a Kirby-Bauer disk diffusion test to determine the susceptibility of a bacterial isolate to several antibiotics. What does a large zone of inhibition around a disk indicate?

Accepted Answer

The bacteria are highly susceptible to the antibiotic.

Question 7

Which equation is used to calculate the minimum inhibitory concentration (MIC) in a broth dilution test?

Accepted Answer

$$MIC = 	ext{lowest concentration of antibiotic that inhibits visible growth}$$

Question 8

A patient develops a superinfection after broad-spectrum antibiotic therapy. Which of the following best explains this phenomenon?

Accepted Answer

Normal microbiota are disrupted, allowing resistant organisms to proliferate.

Question 9

Which of the following is a major disadvantage of broad-spectrum antibiotics?

Accepted Answer

They can disrupt normal microbiota, leading to secondary infections.

Question 10

A microbiologist is testing the minimum bactericidal concentration (MBC) of an antibiotic. Which of the following best describes the MBC?

Accepted Answer

The lowest concentration of antibiotic that kills the bacteria.

Question 11

Which of the following mechanisms is most likely responsible for bacterial resistance to beta-lactam antibiotics?

Accepted Answer

Production of beta-lactamase enzymes that hydrolyze the antibiotic.

Question 12

A patient is treated with an antibiotic that targets the 50S ribosomal subunit. Which process is most directly inhibited?

Accepted Answer

Protein synthesis (translation)

Question 13

Which of the following is a key benefit of using narrow-spectrum antibiotics?

Accepted Answer

They minimize disruption of normal microbiota.

Question 14

A hospital isolates a strain of bacteria that is resistant to multiple antibiotics. Which of the following is the most likely explanation for this resistance?

Accepted Answer

The bacteria have acquired resistance genes through horizontal gene transfer.

Question 15

Which of the following best describes the therapeutic index (TI) of an antimicrobial drug?

Accepted Answer

$$TI = \frac{	ext{toxic dose for humans}}{	ext{minimum effective dose for pathogen}}$$

Question 16

A patient is prescribed a sulfonamide antibiotic. What is the primary target of this drug?

Accepted Answer

Folic acid synthesis pathway

Question 17

Which of the following is a major advantage of using the E-test over the Kirby-Bauer disk diffusion method?

Accepted Answer

The E-test provides a precise MIC value for the antibiotic.

Question 18

A patient with a urinary tract infection is treated with a drug that disrupts bacterial DNA gyrase. What is the most likely effect of this drug?

Accepted Answer

It inhibits DNA replication, preventing bacterial cell division.

Question 19

Which of the following is the best strategy to prevent the development of antibiotic resistance in clinical settings?

Accepted Answer

Use antibiotics only when necessary and complete the prescribed course.

Study Notes: Controlling Microbial Growth in the Body – Antimicrobial Drugs

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