A 32-year-old woman goes to an emergency depament because she has developed severe, watery diarrhea. About 36 hours later, she developed vomiting and an abrupt, painless, watery diarrhea. The volume of diarrhea has been copious, and she has subsequently developed intense thirst, oliguria, muscle cramps, and weakness. At the time of being seen in the emergency depament, she is noted to have marked loss of tissue turgor, sunken eyes, and wrinkling of the skin of her fingers. Laboratory studies demonstrate hemoconcentration and severe metabolic acidosis with potassium depletion. An organism cultured from the patient’s stool is subsequently characterized as an oxidase-positive, gram-negative curved rod with polar flagella that shows “shooting star” mobility and grows best on TCBS medium. Which of the following is the most likely pathogen?
A 32-year-old woman goes to an emergency depament because she has developed severe, watery diarrhea. About 36 hours later, she developed vomiting and an abrupt, painless, watery diarrhea. The volume of diarrhea has been copious, and she has subsequently developed intense thirst, oliguria, muscle cramps, and weakness. At the time of being seen in the emergency depament, she is noted to have marked loss of tissue turgor, sunken eyes, and wrinkling of the skin of her fingers. Laboratory studies demonstrate hemoconcentration and severe metabolic acidosis with potassium depletion. An organism cultured from the patient’s stool is subsequently characterized as an oxidase-positive, gram-negative curved rod with polar flagella that shows “shooting star” mobility and grows best on TCBS medium. Which of the following is the most likely pathogen?
💡 Explanation
**Core Concept**
The patient's symptoms suggest a severe gastrointestinal infection, likely caused by a pathogen that produces a toxin leading to profuse watery diarrhea, dehydration, and electrolyte imbalances. The described organism's characteristics, such as being an oxidase-positive, gram-negative curved rod, are key to identifying the pathogen.
**Why the Correct Answer is Right**
The organism's description matches Vibrio cholerae, a gram-negative curved rod that produces cholera toxin (CT). CT stimulates adenylate cyclase in intestinal epithelial cells, leading to a massive efflux of chloride and water into the intestinal lumen, resulting in profuse, watery diarrhea. The toxin also causes hemoconcentration, metabolic acidosis, and potassium depletion due to the loss of potassium ions in the stool. The "shooting star" mobility is characteristic of Vibrio species, and TCBS (Thiosulfate-citrate-bile salts-sucrose) agar is selective for Vibrio species, including V. cholerae.
**Why Each Wrong Option is Incorrect**
**Option A:** While Shigella species can cause severe diarrhea, they are gram-negative rods but lack the characteristic curved shape and "shooting star" mobility of Vibrio species. Shigella species also typically do not produce a toxin leading to the same level of electrolyte imbalance and metabolic acidosis seen in this patient.
**Option B:** Enteropathogenic E. coli (EPEC) can cause severe diarrhea, particularly in infants, but they are gram-negative rods without the characteristic curved shape or "shooting star" mobility of Vibrio species. Additionally, EPEC infections typically do not produce the same level of electrolyte imbalance and metabolic acidosis seen in this patient.
**Option C:** Campylobacter species can cause severe diarrhea, but they are gram-negative, curved rods with a different morphology than Vibrio species. They also typically do not produce a toxin leading to the same level of electrolyte imbalance and metabolic acidosis seen in this patient.
**Option D:** Salmonella species can cause severe diarrhea, but they are gram-negative rods without the characteristic curved shape or "shooting star" mobility of Vibrio species. They also typically do not produce a toxin leading to the same level of electrolyte imbalance and metabolic acidosis seen in this patient.
**Clinical Pearl / High-Yield Fact**
Cholera toxin (CT) is a potent stimulator of adenylate cyclase, leading to a massive efflux of chloride and water into the intestinal lumen, resulting in profuse, watery diarrhea. CT is also responsible for the electrolyte imbalances and metabolic acidosis seen in cholera.
**Correct Answer: D. Vibrio cholerae**
✓ Correct Answer: D. Vibrio cholerae
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