This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Pathology
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? 
Select and explain. 
A. Cryptosporidium parvum, B. Entamoeba histolytica, C. Staphylococcus aureus, D. Vibrio parahaemolyticus
D: Vibrio parahaemolyticus
Answer: D: Vibrio parahaemolyticus 
Explanation: 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.