Q: Which equation best represents the acid production by Streptococcus mutans during carbohydrate fermentation, leading to enamel decay?

$$\text{C}_{6}\text{H}_{12}\text{O}_{6} \rightarrow 2\text{C}_{2}\text{H}_{4}\text{O}_{2} + 2\text{CO}_{2}$$

Q: Which equation best represents the loss of fluid in cholera, and how should it be managed?

$$\text{Fluid loss} = \text{Stool volume} \times \text{frequency}$$; managed by oral rehydration therapy

Q: Which equation best represents the infective dose for Vibrio cholerae, and why are people with low stomach acid more susceptible?

$$\text{Infective dose} = 10$$^{8}$$ to 10$$^{10}$; low stomach acid increases susceptibility by reducing acid-mediated bacterial killing

Question 1

Which bacterium is most responsible for the formation of dental caries due to its ability to metabolize carbohydrates, tolerate high acidity, and synthesize dextran?

Accepted Answer

Streptococcus mutans

Question 2

A patient presents with 'rice water stools' and severe dehydration after drinking contaminated water. Which pathogen and mechanism are most likely responsible for these symptoms?

Accepted Answer

Vibrio cholerae; secretion of chloride, bicarbonate, and water due to cholera toxin

Question 3

Which defense mechanism in the small intestine is responsible for producing antibacterial proteins and enzymes?

Accepted Answer

Paneth cells

Question 4

Staphylococcal food poisoning is often associated with which of the following foods, and why does reheating not prevent illness?

Accepted Answer

Custards; toxins are heat-resistant and remain after bacteria are killed

Question 5

Which equation best represents the acid production by Streptococcus mutans during carbohydrate fermentation, leading to enamel decay?

Accepted Answer

$$	ext{C}_{6}	ext{H}_{12}	ext{O}_{6} ightarrow 2	ext{C}_{2}	ext{H}_{4}	ext{O}_{2} + 2	ext{CO}_{2}$$

Question 6

A child develops diarrhea, fever, and abdominal cramps after contact with a pet turtle. Which organism is most likely responsible, and what is the primary mode of transmission?

Accepted Answer

Salmonella; fecal-oral route

Question 7

Which of the following statements about Clostridium difficile is correct?

Accepted Answer

It is commonly associated with extended antibiotic use and produces exotoxins

Question 8

Which viral disease is characterized by inflammation of the parotid salivary glands, painful swallowing, and can lead to orchitis in post-pubescent males?

Accepted Answer

Mumps

Question 9

A patient with a history of antibiotic use develops severe diarrhea and colitis. Which diagnostic test is most appropriate for confirming Clostridium difficile infection?

Accepted Answer

Immunoassay for exotoxins

Question 10

Which protozoan disease is diagnosed using the string test and is characterized by prolonged diarrhea, flatulence, and a distinctive hydrogen sulfide smell?

Accepted Answer

Giardiasis

Question 11

Which hepatitis virus is most likely to cause chronic infection and is transmitted primarily by blood, with no vaccine available?

Accepted Answer

Hepatitis C

Question 12

Which organism is a potent urease producer, allowing it to survive in the acidic environment of the stomach and cause peptic ulcers?

Accepted Answer

Helicobacter pylori

Question 13

Which equation best represents the loss of fluid in cholera, and how should it be managed?

Accepted Answer

$$	ext{Fluid loss} = 	ext{Stool volume} 	imes 	ext{frequency}$$; managed by oral rehydration therapy

Question 14

Which helminthic disease is diagnosed by finding eggs in the perianal region and is characterized by nocturnal itching?

Accepted Answer

Pinworm infection (Enterobius vermicularis)

Question 15

Which bacterial pathogen is most likely to cause hemolytic uremic syndrome (HUS) in children, and what is the primary virulence factor?

Accepted Answer

Escherichia coli O157:H7; shiga toxin

Question 16

Which protozoan disease is life-threatening in immunocompromised patients and is transmitted via contaminated recreational and drinking water?

Accepted Answer

Cryptosporidiosis

Question 17

Which bacterial disease is characterized by blood and mucus in stool, abdominal cramps, and is caused by a pathogen that rarely invades the bloodstream?

Accepted Answer

Shigellosis (Bacillary Dysentery)

Question 18

Which equation best represents the infective dose for Vibrio cholerae, and why are people with low stomach acid more susceptible?

Accepted Answer

$$	ext{Infective dose} = 10$$^{8}$$ to 10$$^{10}$; low stomach acid increases susceptibility by reducing acid-mediated bacterial killing

Question 19

Which organism is most likely to cause severe anemia and lethargic behavior due to blood feeding in the intestines, and how is it contracted?

Accepted Answer

Necator americanus (hookworm); penetration of skin from contaminated soil

Diseases of the Digestive System: Microbiology Study Notes

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