Question 1

Which of the following is a primary defense mechanism of the gastrointestinal (GI) tract against microbial infection?

Accepted Answer

Secretion of hydrochloric acid (HCl) in the stomach

Question 2

A patient presents with severe, watery diarrhea after eating fried rice that was kept warm for several hours. Which organism and toxin are most likely responsible?

Accepted Answer

Bacillus cereus, heat-stable emetic toxin

Question 3

Which of the following best explains why antibiotics are contraindicated in infections with shiga-toxin-producing E. coli (STEC)?

Accepted Answer

Antibiotics may increase the release of shiga toxin, worsening pathology

Question 4

Which of the following is a function of the normal biota in the large intestine?

Accepted Answer

Synthesis of vitamin K by Escherichia coli

Question 5

A 7-year-old child develops bloody diarrhea and hemolytic uremic syndrome (HUS) after eating undercooked hamburger. Which pathogen is most likely responsible?

Accepted Answer

Escherichia coli O157:H7

Question 6

Which of the following statements about Salmonella is TRUE?

Accepted Answer

It is motile and ferments glucose with acid and sometimes gas

Question 7

Which of the following best describes the pathogenesis of Vibrio cholerae?

Accepted Answer

It produces cholera toxin, which causes cells to secrete electrolytes and water

Question 8

A patient develops pseudomembranous colitis after a course of broad-spectrum antibiotics. Which organism is most likely responsible?

Accepted Answer

Clostridium difficile

Question 9

Which of the following is the most effective initial treatment for severe dehydration caused by cholera?

Accepted Answer

Oral rehydration therapy (ORT) with a solution of sodium chloride, sodium bicarbonate, potassium chloride, and glucose

Question 10

Which of the following is a distinguishing feature of Shigella infection compared to Salmonella infection?

Accepted Answer

Shigella often causes dysentery with blood and mucus in stools

Question 11

Which of the following best explains why the stomach was previously thought to be sterile?

Accepted Answer

The very low pH due to hydrochloric acid

Question 12

Which of the following is a key virulence factor for Campylobacter jejuni?

Accepted Answer

Production of a heat-labile enterotoxin that stimulates secretory diarrhea

Question 13

A patient presents with greasy, malodorous stools and flatulence after drinking untreated stream water. Which protozoan is most likely responsible?

Accepted Answer

Giardia lamblia

Question 14

Which of the following is a major function of the large intestine?

Accepted Answer

Absorption of water and electrolytes

Question 15

Which of the following best describes the role of alpha-hemolytic streptococci in the oral cavity?

Accepted Answer

They are the first colonizers of the tooth surface after cleaning

Question 16

Which of the following is the most common cause of child deaths from diarrheal diseases worldwide?

Accepted Answer

Rotavirus

Question 17

Which of the following is a characteristic of food poisoning caused by Staphylococcus aureus?

Accepted Answer

Symptoms appear 1–6 hours after ingestion and are self-limiting

Question 18

Which of the following is a common predisposing factor for periodontitis?

Accepted Answer

Mineralization of dental plaque to form calculus

Question 19

Which of the following best describes the pathogenesis of Entamoeba histolytica in the human host?

Accepted Answer

It secretes enzymes that dissolve tissues, causing flask-shaped ulcers in the colon

Question 20

Which of the following is the best method for preventing transmission of Giardia lamblia?

Accepted Answer

Boiling or treating water with iodine before drinking

Microorganisms of the Mouth & Pathogenic Microorganisms of the GI Tract: Structure, Defenses, and Diseases

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