A 34-year-old woman presents to the outpatient clinic with a 4-day history of watery diarrhea, abdominal cramping, and low-grade fever. She recently attended a picnic where she consumed undercooked chicken. She denies bloody stools or recent antibiotic use. Vitals signs are blood pressure 106/64 mmHg, heart rate 120 beats/minute, and temperature 37.8°C. Physical examination reveals tachycardia and generalized right lower quadrant abdominal tenderness to palpation. Laboratory studies include a serum creatinine of 1.1 mg/dL, blood urea nitrogen of 37 mg/dL, alanine aminotransferase of 38 IU/L, and aspartate aminotransferase of 25 IU/L. Stool culture grows gram-negative, comma-shaped bacilli that are oxidase-positive and grow on thiosulfate–citrate–bile salts–sucrose agar with yellow colonies.
Which of the following is the most likely causative organism?
The correct answer is:
A) Campylobacter jejuni
Campylobacter jejuni causes foodborne gastroenteritis with watery diarrhea and abdominal cramping, and is often linked to poultry. Stool culture shows gram-negative, comma-shaped, oxidase-positive bacilli forming yellow colonies on Thiosulfate–citrate–bile salts–sucrose agar.
Answer choice B: Clostridium difficile, is incorrect. Clostridium difficile typically causes diarrhea following antibiotic use, is gram-positive, and forms toxin-mediated pseudomembranous colitis.
Answer choice C: Salmonella enterica, is incorrect. Salmonella is a gram-negative, non-lactose-fermenting bacillus, is not comma-shaped, and grows on selective media like Hektoen enteric (HE) agar.
Answer choice D: Shigella flexneri, is incorrect. Shigella causes bloody diarrhea, is a gram-negative, non-motile bacillus, and does not grow on Thiosulfate–citrate–bile salts–sucrose or show oxidase positivity.
Answer choice E: Vibrio cholerae, is incorrect. Vibrio cholerae causes profuse rice-water diarrhea, and grows on Thiosulfate–citrate–bile salts–sucrose with yellow colonies, but is associated with contaminated water, not poultry, and is less likely in this clinical setting.
Key Learning Point
Campylobacter jejuni causes foodborne diarrhea (poultry-linked), identified by gram-negative, comma-shaped, oxidase-positive bacilli with yellow Thiosulfate–citrate–bile salts–sucrose colonies. Self-limiting; azithromycin for severe cases, prevents complications like Guillain-Barré syndrome.
