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 secreted by both Gram-positive and Gram-negative bacteria.

Question 2

A patient presents with rapidly spreading necrotizing fasciitis. Which enzyme produced by the causative agent is responsible for lysing erythrocytes, and what type of hemolysis does this organism cause on blood agar?

Accepted Answer

Streptolysin O; beta hemolysis

Question 3

Which of the following best describes the mechanism of action of botulinum toxin?

Accepted Answer

It inhibits the release of acetylcholine at neuromuscular junctions, causing flaccid paralysis.

Question 4

Why are botulism and tetanus considered intoxications rather than infections?

Accepted Answer

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

Question 5

A patient with tetanus presents with trismus and opisthotonos. What is the mechanism of action of tetanospasmin, and what type of paralysis does it cause?

Accepted Answer

Blocks inhibitory neurotransmitter release, causing spastic paralysis.

Question 6

Which of the following best explains why Clostridium botulinum and Clostridium tetani are able to survive in unfavorable environments?

Accepted Answer

They form endospores, which are resistant to heat, desiccation, and chemicals.

Question 7

A 5-year-old child presents with pharyngitis, erythema, exudate, and lymphadenopathy. Which organism is most likely responsible, and what type of hemolysis does it produce on sheep blood agar?

Accepted Answer

Streptococcus pyogenes; beta hemolysis

Question 8

Helicobacter pylori is associated with which type of cancer, and what virulence factor allows it to survive in the acidic environment of the stomach?

Accepted Answer

Gastric adenocarcinoma; urease production

Question 9

Which of the following best describes the pathogenesis of Staphylococcus aureus food poisoning?

Accepted Answer

Ingestion of preformed, heat-stable enterotoxin that stimulates the vomiting center in the brain.

Question 10

A patient develops severe diarrhea after antibiotic therapy. Which bacterium is most likely responsible, and what is the rationale for using a fecal transplant in severe cases?

Accepted Answer

Clostridium difficile; to restore normal gut microbiota and outcompete C. difficile.

Question 11

Which of the following best explains why cranberry juice may help prevent urinary tract infections caused by Escherichia coli?

Accepted Answer

It contains compounds that inhibit the adhesion of E. coli fimbriae to uroepithelial cells.

Question 12

Treponema pallidum, the causative agent of syphilis, is best described as:

Accepted Answer

A spirochete with a helical cell shape.

Question 13

Chlamydia trachomatis is considered an atypical bacterium because:

Accepted Answer

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

Question 14

Which of the following best describes the difference between the elementary body and reticulate body forms of Chlamydia trachomatis?

Accepted Answer

The elementary body is the infectious, extracellular form; the reticulate body is the replicative, intracellular form.

Question 15

A 25-year-old woman is diagnosed with pelvic inflammatory disease (PID) after an asymptomatic chlamydial infection. What percentage of women with chlamydia are typically asymptomatic, and what is the significance of this for disease transmission?

Accepted Answer

Up to 75% are asymptomatic, allowing for silent spread of the infection.

Question 16

Which of the following best describes the action of shiga toxin produced by Escherichia coli O157:H7?

Accepted Answer

It inhibits protein synthesis in host cells, leading to cell death and hemorrhagic colitis.

Question 17

Which of the following is the best way to prevent botulism from home-canned foods?

Accepted Answer

Heating foods to at least $$100^{\circ}C$ for 10 minutes to destroy the toxin.

Question 18

Which of the following is a clinical feature of secondary syphilis?

Accepted Answer

Widespread rash including palms and soles.

Question 19

Which of the following best describes the function of human tetanus immune globulin (TIG) in the treatment of tetanus?

Accepted Answer

It provides passive immunity by neutralizing unbound tetanospasmin toxin.

Question 20

Which of the following best explains why anti-diarrheal medications should be avoided in infections with E. coli O157:H7?

Accepted Answer

They can prolong toxin exposure and increase the risk of hemolytic uremic syndrome.

Microbiology Unit III: Bacterial Diseases – Study Guidance

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