A healthy 21-year-old woman develops a profuse, watery diarrhea 1 day after a meal of raw oysters. On physical examination, her temperature is 37.5deg C. A stool sample is negative for occult blood. There is no abdominal distention or tenderness, and bowel sounds are present. Diarrhea subsides over the next 3 days. Which of the following organisms is most likely to produce these findings?

Raw or poorly cooked shellfish can be the source of Vibrio parahaemolyticus, which tends to produce milder diarrhea than Vibrio cholerae. Vibrio organisms produce a toxin that increases adenylate cyclase, leading to chloride ion secretion and osmotic diarrhea. Cryptosporidium as a cause of watery diarrhea is most often found in immunocompromised individuals. Entamoeba histolytica produces colonic mucosal invasion along with exudation and ulceration; stools contain blood and mucus. Staphylococcus aureus can produce food poisoning through the elaboration of an enterotoxin that causes explosive vomiting and diarrhea within 2 hours after ingestion. Yersinia enterocolitica is invasive and can produce extraintestinal infection.