$$TI = \frac{\text{toxic dose}}{\text{effective dose}}$$

Question 1

Which scientist is credited with the discovery of penicillin, and what was the source organism?

Accepted Answer

Alexander Fleming; Penicillium chrysogenum

Question 2

Which of the following best describes a semisynthetic antimicrobial agent?

Accepted Answer

A naturally occurring antibiotic that is chemically altered to improve its properties

Question 3

Why are antibiotics generally ineffective against the common cold?

Accepted Answer

The common cold is caused by viruses, which lack the structures targeted by antibiotics

Question 4

Which of the following is a major mechanism by which beta-lactam antibiotics inhibit bacterial growth?

Accepted Answer

Prevention of cross-linkage of peptidoglycan subunits in the cell wall

Question 5

A patient is prescribed vancomycin for a Gram-positive bacterial infection. What is the primary mode of action of vancomycin?

Accepted Answer

Interferes with bridges that link NAM subunits in peptidoglycan

Question 6

Which equation correctly represents the calculation of the therapeutic index (TI) for an antimicrobial drug?

Accepted Answer

$$TI = \frac{	ext{toxic dose}}{	ext{effective dose}}$$

Question 7

Which antimicrobial agent selectively binds to isoleucyl-tRNA synthetase, preventing the loading of isoleucine in Gram-positive bacteria?

Accepted Answer

Mupirocin

Question 8

Why are drugs that inhibit peptidoglycan synthesis only effective against growing bacterial cells?

Accepted Answer

They prevent bacteria from increasing the amount of peptidoglycan, which only occurs during cell growth

Question 9

Which of the following drugs acts by disrupting the cytoplasmic membranes of Gram-negative bacteria and is toxic to human kidneys?

Accepted Answer

Polymyxin

Question 10

A hospital patient develops a secondary infection after broad-spectrum antibiotic treatment. What is the most likely cause?

Accepted Answer

The antibiotic killed normal flora, reducing microbial antagonism

Question 11

Which test is used to determine the minimum concentration of an antimicrobial agent required to inhibit the growth of a microorganism?

Accepted Answer

Minimum inhibitory concentration (MIC) test

Question 12

Which of the following mechanisms is NOT a way bacteria acquire resistance to antimicrobial drugs?

Accepted Answer

Direct transformation of host DNA into bacterial DNA

Question 13

Which of the following is an example of synergism in antimicrobial therapy?

Accepted Answer

Two drugs administered together have a greater effect than either alone

Question 14

Which of the following statements about cross resistance is correct?

Accepted Answer

It occurs when a pathogen is resistant to drugs with similar structures

Question 15

Which of the following is a reason why physicians do NOT always prescribe the antimicrobial with the largest zone of inhibition?

Accepted Answer

Other factors such as toxicity, route of administration, and spectrum of action must be considered

Question 16

Which of the following is a correct statement about the action of quinolones and fluoroquinolones?

Accepted Answer

They act against prokaryotic DNA gyrase, inhibiting DNA replication

Question 17

Which of the following is a plausible reason why an individual bacterium does NOT develop resistance in response to an antibiotic?

Accepted Answer

Resistance arises from random mutations or gene acquisition, not from direct exposure to antibiotics

Question 18

Which of the following drugs disrupts fungal cell membranes by binding to ergosterol?

Accepted Answer

Amphotericin B

Question 19

A patient is prescribed a combination of two antimicrobial agents. What is the most likely outcome if the drugs exhibit antagonism?

Accepted Answer

The drugs interfere with each other's effectiveness, reducing overall efficacy

Question 20

Which of the following is a property of an ideal antimicrobial agent?

Accepted Answer

It is selectively toxic against a wide range of pathogens

Ch 10 - Antimicrobial Drugs: History, Sources & Types

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