lecture 8 and 9

Question 1

2. You’re a public health epidemiologist who is called to investigate
   an outbreak of bloody diarrhea in 16 people. You find that it is
   associated with eating rare hamburgers in a particular fast-food
   restaurant. A culture of the remaining uncooked hamburger
   grows a gram-negative rod that produces a dark purple colony
   on EMB agar, which is evidence that it ferments lactose. Which
   one of the following bacteria is the most likely cause of this
   outbreak?
   (A) Escherichia coli
   (B) Salmonella enterica
   (C) Salmonella typhi
   (D) Shigella dysenteriae
   (E) Vibrio cholerae

Answer 1

(A) Escherichia coli

Question 2

5. Regarding the members of the family Enterobacteriaceae, which
   one of the following statements is the most accurate?
   (A) All members of the family are anaerobic, which means they
   must be cultured in the absence of oxygen.
   (B) All members of the family ferment lactose, which is an
   important diagnostic criterion in the clinical laboratory.
   (C) All members of the family have endotoxin, an important
   pathogenetic factor.
   (D) All members of the family produce an enterotoxin, which
   ADP-ribosylates a G protein in human enterocytes.

Answer 2

(C) All members of the family have endotoxin, an important

pathogenetic factor.

Question 3

6. You’re on a summer program working in a clinic in a small village in Ecuador. There is an outbreak of cholera, and your patient
   has massive diarrhea and a blood pressure of 70/40 mm Hg. Which
   one of the following would be the most appropriate action to
   take?
   (A) Administer antimotility drugs to diminish the diarrhea.
   (B) Administer intravenous saline to replenish volume.
   (C) Administer tetracycline to kill the organism.
   (D) Perform stool cultures and fecal leukocyte tests to make an
   accurate diagnosis.

Answer 3

(B) Administer intravenous saline to replenish volume.

Question 4

7. Your patient is a 20-year-old woman with diarrhea. She has just
   returned to the United States from a 3-week trip to Peru, where
   she ate some raw shellfish at the farewell party. She now has
   severe watery diarrhea, perhaps 20 bowel movements a day, and
   is feeling quite weak and dizzy. Her stool is guaiac-negative, a
   test that determines whether there is blood in the stool. A Gram
   stain of the stool reveals curved gram-negative rods. Culture of
   the stool on MacConkey’s agar shows colorless colonies. Which
   one of the following bacteria is the most likely cause of this
   infection?
   (A) Escherichia coli
   (B) Helicobacter pylori
   (C) Proteus mirabilis
   (D) Pseudomonas aeruginosa
   (E) Vibrio cholerae

Answer 4

(E) Vibrio cholerae

Question 5

8. Your patient is a 6-year-old boy with bloody diarrhea for the
   past 2 days accompanied by fever to 40°C and vomiting. He has
   a pet corn snake. Blood culture and stool culture from the boy
   and stool culture from the snake (taken very carefully!) revealed
   the same organism. The cultures grew a gram-negative rod that
   formed colorless colonies on EMB agar. Which one of the following bacteria is the most likely cause of this infection?
   (A) Helicobacter pylori
   (B) Proteus mirabilis
   (C) Salmonella enterica
   (D) Shigella dysenteriae
   (E) Vibrio cholerae

Answer 5

(C) Salmonella enterica

Question 6

12. Your patient in the gastrointestinal clinic is a 50-year-old insurance salesman with what he describes as a “sour stomach” for
    several months. Antacids relieve the symptoms. After taking a
    complete history and doing a physical examination, you discuss
    the case with your resident, who suggests doing a urea breath
    test, which tests for the presence of urease. Which one of the following bacteria does the resident think is the most likely cause
    of the patient’s disease?
    (A) Helicobacter pylori
    (B) Proteus mirabilis
    (C) Salmonella enterica
    (D) Serratia marcescens
    (E) Shigella dysenteriae

Answer 6

(A) Helicobacter pylori