Question 1

Which of the following best differentiates endotoxins from exotoxins?

Accepted Answer

Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria, while exotoxins are proteins actively secreted by bacteria.

Question 2

Streptococcus pyogenes is known to cause necrotizing fasciitis. Which enzyme does it use to lyse erythrocytes, and what type of hemolysis does it produce on sheep blood agar?

Accepted Answer

It uses streptolysin O and produces beta hemolysis.

Question 3

Which exotoxin produced by Streptococcus pyogenes helps it evade the host immune system by destroying neutrophils?

Accepted Answer

Streptolysin S

Question 4

Clostridium tetani and Clostridium botulinum require which type of environment for growth, and what structure do they form when conditions are unfavorable?

Accepted Answer

Anaerobic environment; they form endospores.

Question 5

Botulism and tetanus are considered intoxications rather than infections because:

Accepted Answer

The diseases are caused by the toxins produced, not by bacterial growth in the host.

Question 6

Botulinum toxin is classified as which type of exotoxin, and what is its mechanism of action?

Accepted Answer

Type III exotoxin; it inhibits acetylcholine release at neuromuscular junctions.

Question 7

A patient presents with nystagmus and flaccid paralysis after consuming improperly canned food. Which bacterial toxin is responsible, and what is the best prevention method?

Accepted Answer

Botulinum toxin; proper heating and canning of food to destroy endospores.

Question 8

Which of the following best describes the mechanism of tetanospasmin and the resulting clinical presentation?

Accepted Answer

It blocks inhibitory neurotransmitter release, causing spastic paralysis.

Question 9

Which clinical features are associated with tetanus, and what is the typical route of entry for Clostridium tetani endospores?

Accepted Answer

Trismus and opisthotonos; entry through deep puncture wounds contaminated with soil.

Question 10

Which of the following best defines 'hemorrhagic colitis' caused by E. coli O157:H7, and what is the role of shiga toxin?

Accepted Answer

It is severe inflammation of the colon with bloody diarrhea; shiga toxin damages endothelial cells in the colon.

Question 11

Which bacterium is most commonly associated with antibiotic-associated diarrhea, and how does antibiotic use facilitate its infection?

Accepted Answer

Clostridium difficile; antibiotics disrupt normal gut flora, allowing C. difficile to proliferate.

Question 12

Which of the following best explains the rationale for fecal transplant in severe cases of Clostridium difficile infection?

Accepted Answer

It restores the normal gut microbiota, outcompeting C. difficile.

Question 13

Which of the following is the most common causative agent of urinary tract infections (UTIs), and what virulence factor allows it to adhere to urinary tract epithelial cells?

Accepted Answer

Escherichia coli; fimbriae (pili).

Question 14

How does cranberry juice help prevent UTIs caused by E. coli?

Accepted Answer

It contains compounds that inhibit E. coli fimbriae from binding to urinary tract cells.

Question 15

Treponema pallidum, the causative agent of syphilis, has a unique cell shape. What is this shape, and what is a 'chancre'?

Accepted Answer

Spirochete; a painless ulcer at the site of infection.

Question 16

Chlamydia trachomatis is considered an atypical bacterium because:

Accepted Answer

It lacks a peptidoglycan cell wall and is an obligate intracellular pathogen.

Question 17

Chlamydia is often called the 'silent disease.' What percentage of infected men and women typically show no symptoms?

Accepted Answer

About 50% of men and 80% of women.

Question 18

Which form of Chlamydia trachomatis is infectious and enters host cells, and which form replicates inside the cell?

Accepted Answer

Elemental body is infectious; reticulate body replicates.

Question 19

Which of the following best describes the clinical features and transmission of trachoma caused by Chlamydia trachomatis?

Accepted Answer

It causes chronic conjunctivitis leading to blindness; transmitted by direct contact with infected secretions.

Microbiology Unit III Study Guide: Bacterial Diseases and Infections

Study Guide - Practice Questions

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