Q: Which equation represents the calculation of the minimum inhibitory concentration (MIC) in a dilution test?

$$MIC = \frac{\text{amount of drug (\mu g)}}{\text{volume of solution (ml)}}$$

Question 1

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

Accepted Answer

Drugs kill or inhibit microbial cells without simultaneously damaging host tissues.

Question 2

Which microbial genus is the source of both penicillins and griseofulvin?

Accepted Answer

Penicillium

Question 3

A patient is prescribed a broad-spectrum antibiotic for a mixed infection. Which drug is most likely to be effective against both Gram-positive and Gram-negative bacteria?

Accepted Answer

Tetracycline

Question 4

Which of the following drugs acts by inhibiting the synthesis of peptidoglycan, leading to cell wall lysis?

Accepted Answer

Penicillins and cephalosporins

Question 5

Why are sulfonamides selectively toxic to bacteria but not to human cells?

Accepted Answer

Bacteria synthesize their own folic acid, while human cells obtain it from the diet.

Question 6

Which of the following is a mechanism by which bacteria acquire drug resistance?

Accepted Answer

Transfer of resistance (R) factors via plasmids

Question 7

A physician prescribes ampicillin for a Gram-negative infection. What property of ampicillin makes it suitable for this use?

Accepted Answer

It is a semisynthetic penicillin with a broader spectrum that can cross the outer membrane of Gram-negative bacteria.

Question 8

Which class of antibiotics works by binding to the 30S ribosomal subunit and causing misreading of mRNA?

Accepted Answer

Aminoglycosides

Question 9

What is the main reason less than 1% of known antibiotics are clinically useful?

Accepted Answer

Most antibiotics are toxic to host cells or lack sufficient efficacy.

Question 10

Which of the following statements about the Kirby-Bauer test is correct?

Accepted Answer

It measures the zone of inhibition around antibiotic wafers to determine bacterial susceptibility.

Question 11

A patient with tuberculosis is treated with streptomycin. What is the mechanism of action of this drug?

Accepted Answer

It binds to the 30S ribosomal subunit, causing misreading of mRNA and faulty protein synthesis.

Question 12

Which equation represents the calculation of the minimum inhibitory concentration (MIC) in a dilution test?

Accepted Answer

$$MIC = \frac{	ext{amount of drug (\mu g)}}{	ext{volume of solution (ml)}}$$

Question 13

Which of the following practices contributes most to the development of antibiotic resistance in bacteria?

Accepted Answer

Stopping antibiotic treatment early, before the full course is completed

Question 14

Which drug is a synthetic analog that blocks the synthesis of folic acid in bacteria?

Accepted Answer

Sulfonamides

Question 15

Which of the following is a correct statement about antiviral drugs for influenza?

Accepted Answer

They block neuraminidase, preventing the virus from being released from infected cells.

Question 16

Which of the following is a mechanism by which HIV drugs inhibit viral replication?

Accepted Answer

Competitive inhibition by nucleoside analogs that terminate DNA synthesis

Question 17

Which of the following best explains why fungal infections are difficult to treat with selective toxicity?

Accepted Answer

Fungal cells are eukaryotic and share many similarities with human cells.

Question 18

A patient is diagnosed with a urinary tract infection caused by Gram-negative bacteria. Which drug class is most likely prescribed due to its broad-spectrum activity and mechanism of inhibiting DNA gyrase?

Accepted Answer

Quinolones

Question 19

Which of the following is a real-world consequence of farmers giving animal feed containing antibiotics to livestock?

Accepted Answer

It increases the prevalence of antibiotic-resistant bacteria in the environment.

Question 20

Which of the following is a correct multi-step process for the development of drug resistance in bacteria?

Accepted Answer

Spontaneous mutations in chromosomal genes followed by acquisition of resistance genes via plasmid transfer

Antimicrobial Drugs: Principles, Sources, and Spectrum (Microbiology Chapter 12 Study Notes)

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