Question 1

Which of the following best describes the difference between endotoxins and exotoxins?

Accepted Answer

Exotoxins are secreted proteins that cause specific effects, while endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria and cause generalized inflammation.

Question 2

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

Accepted Answer

It uses streptolysin and causes beta hemolysis.

Question 3

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

Accepted Answer

Streptolysin O

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; 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 a type of which exotoxin, and what is its mechanism of action?

Accepted Answer

Type III exotoxin; blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis

Question 7

Which of the following best describes the term 'heat-labile' with respect to botulinum toxin?

Accepted Answer

The toxin is destroyed by heat, so proper cooking prevents intoxication.

Question 8

Tetanospasmin, the exotoxin produced by Clostridium tetani, causes which type of paralysis and by what mechanism?

Accepted Answer

Spastic paralysis by inhibiting inhibitory neurotransmitter release (glycine and GABA)

Question 9

Which vaccine contains tetanus toxoid and is used to prevent tetanus?

Accepted Answer

DTaP vaccine

Question 10

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 cancer; produces urease

Question 11

Which strain of Escherichia coli causes hemorrhagic colitis and is associated with AE lesions and the production of Shiga toxin?

Accepted Answer

E. coli O157:H7

Question 12

Why should anti-diarrheal medications NOT be used in cases of E. coli O157:H7 infection?

Accepted Answer

They increase toxin absorption and risk of hemolytic uremic syndrome.

Question 13

Clostridium difficile causes antimicrobial-associated diarrhea. How does toxin A alter the intestine?

Accepted Answer

Toxin A damages intestinal mucosa, causing inflammation and fluid secretion.

Question 14

Which of the following best explains why a fecal transplant can be effective in treating severe cases of antibiotic-associated diarrhea caused by Clostridium difficile?

Accepted Answer

It restores the normal microbiota, which outcompete C. difficile for resources.

Question 15

Which bacterium is most commonly responsible for urinary tract infections (UTIs), and what virulence factor allows it to adhere to urinary tract epithelial cells?

Accepted Answer

Escherichia coli; produces fimbriae (pili)

Question 16

How can 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 17

Treponema pallidum, the causative agent of syphilis, has which unique cell shape, and what is the name of the painless lesion seen in primary syphilis?

Accepted Answer

Spirochete; chancre

Question 18

Chlamydia trachomatis is considered an atypical bacterium because:

Accepted Answer

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

Question 19

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 20

Trachoma, caused by Chlamydia trachomatis, affects which body part and by what mechanism?

Accepted Answer

Affects the eye by causing scarring of the conjunctiva

Microbiology Unit III: Bacterial Diseases – Study Guidance

Study Guide - Practice Questions

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