<prompt> 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?Cryptosporidium parvumEntamoeba histolyticaStaphylococcus aureusVibrio parahaemolyticus  <response>: 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. 