Question 1

In the gastrointestinal system, the majority of the bacterial actions that are part of the digestive process occur in the

Accepted Answer

The large intestine is the primary site where bacterial fermentation of indigestible matter occurs, aiding in the digestion process and in the production of certain vitamins.

Question 2

Which of the following organisms are usually considered normal intestinal flora but may become clinically significant when normal GI flora is disturbed due to antibiotic use.

Accepted Answer

D

Question 3

A high dose of organism inoculum is required to establish gastrointestinal disease for all of the following organisms except

Accepted Answer

Shigella spp. require a low inoculum to establish gastrointestinal disease, unlike the other organisms listed, which typically require a higher dose.

Question 4

Which of the following organisms can be normal flora and only causes disease when it produces toxin in the gastrointestinal tract?

Accepted Answer

Clostridium difficile and Staphylococcus aureus can be normal flora and only cause disease when they produce toxins in the gastrointestinal tract.

Question 5

A large cruise ship must end its current voyage early due to an outbreak of nausea, vomiting, and diarrhea among its passengers. Your laboratory is asked to help process stool samples to determine the causative agent of the outbreak. You suspect the causative agent to be

Accepted Answer

Norovirus is a common cause of gastroenteritis outbreaks on cruise ships, characterized by symptoms such as nausea, vomiting, and diarrhea.

Question 6

A 4-year-old female develops diarrhea, and her mother takes her to the pediatrician. The child attends daycare five days a week while the mother works. The family had recently returned from a camping trip where the little girl spoke of catching turtles and lizards. An image of the HE agar plate of the child's stool culture is provided.
 Source: CDC
Given this information , which of the following apply to this organism?

Accepted Answer

The answer of A 4-year-old female develops diarrhea, and her...

Question 7

A stool culture was received from a 34-year-old male who is experiencing diarrhea after a family reunion picnic. The food served included hot dogs, hamburgers, fried chicken, potato salad, baked beans, and various desserts. The image provided shows the Hektoen-enteric agar growth from his culture.
 Source: CDC
Based on these results, your next step in the workup of this stool culture is to

Accepted Answer

The answer of A stool culture was received from a...

Question 8

After a visit to Chicago over Christmas, a couple returns to St. Louis with nausea, diarrhea, and cramping in the lower right quadrant of their abdomens. They admitted to indulging in a family favorite of chitterlings over the holidays. The routine stool culture of both individuals provided the same results:
BAP: all colonies present are oxidase negative and no beta-hemolytic colonies observed
MAC: lactose fermenters and oxidase negative, non-lactose fermenters HE: yellow colonies
PEA: no suspicious colonies
Campy blood agar: no growth
Based on the patient history, the original orders also requested the stool specimens be cultured for an additional enteric pathogen. The processing technician noted the request and added one
Additional agar plate to the routine stool culture media. The additional agar demonstrates the potential enteric pathogen as _________ colonies.

Accepted Answer

The symptoms and the consumption of chitterlings suggest an infection with Yersinia enterocolitica, which typically produces red-centered colonies with clear edges on CIN (Cefsulodin-Irgasan-Novobiocin) agar, the likely additional agar plate used for culturing this pathogen.

Question 9

A stool agar plate incubated at 42°C in an atmosphere of 5% O₂, 10% CO₂, and 85% N₂ grew as a tan colony that tends to follow the streak lines. An image of the Gram stain results of the colonies is provided. Source: CDC You would expect this organism to be

Accepted Answer

The answer of A stool agar plate incubated at 42°C...

Question 10

The blood agar plate of a stool culture is screened using the oxidase test. It is determined that a large, wet, gray colony is oxidase positive. Based on this result, the next agar plate you should examine is the

Accepted Answer

MAC is used to isolate and identify Gram-negative bacteria, which are typically oxidase positive.

Question 11

A 22-year-old male presents to his physician with vomiting and severe, watery diarrhea after spring break in New Orleans, LA. Given this patient history, what additional enteric medium should be added to the routine stool culture?

Accepted Answer

TCBS (Thiosulfate-citrate-bile salts-sucrose) agar is specifically used for the isolation of Vibrio species, which are a common cause of gastroenteritis in coastal regions like New Orleans, especially after consuming raw or undercooked seafood.

Question 12

At 4 pm, a physician requests that you add a culture for Clostridium difficile to a routine stool culture he wrote orders for at 9 am. You will

Accepted Answer

Clostridium difficile infection is best diagnosed through toxin detection rather than culture, as the presence of the bacteria does not necessarily indicate disease; it is the toxins produced by the bacteria that cause symptoms. Toxin detection is more clinically relevant and provides a faster, more accurate diagnosis for patient management.

Question 13

An oxidase negative, non-lactose fermenter isolated from the stool culture of a 3-year-old female with bloody diarrhea. The organism proves to be:
 If it serotypes as a group D, you would identify the organism as

Accepted Answer

The answer of An oxidase negative, non-lactose fermenter isolated from...

Question 14

Based on the Gram stain image of a fecal specimen provided, determine the probable pathogenic mechanism responsible if the diarrhea present is due to an enteric bacterial pathogen.
 Source: CDC

Accepted Answer

The answer of Based on the Gram stain image of...

Question 15

The disease caused by Salmonella typhi differs from that caused by other Salmonella spp. because it

Accepted Answer

Salmonella typhi causes typhoid fever, which is characterized by its ability to penetrate the intestinal mucosa and spread to the bloodstream, leading to systemic infection. Other Salmonella species typically cause gastroenteritis without systemic spread.

Question 16

The disease mechanism of enterotoxigenic E. coli closely resembles that of

Accepted Answer

The disease mechanism of enterotoxigenic E. coli (ETEC) closely resembles that of Vibrio cholerae, as both pathogens produce enterotoxins that cause watery diarrhea by stimulating the secretion of chloride ions into the intestinal lumen, leading to water efflux.

Question 17

E. coli O157:H7 is one example of an ______________________ strain.

Accepted Answer

E. coli O157:H7 is an example of an enterohemorrhagic strain, which is known for causing severe foodborne illness through the production of Shiga toxins, leading to bloody diarrhea and potentially life-threatening complications such as hemolytic uremic syndrome (HUS).

Question 18

The most important initial treatment for diarrhea is

Accepted Answer

The most important initial treatment for diarrhea is the replacement of fluids and electrolytes to prevent dehydration, which can be a serious complication, especially in children and the elderly.

Quiz 35: Gastrointestinal System