A 20 year old man presented with abdominal pain, vomiting and bloody diarrhea, his stool sample grew Escherichia coli in pure culture. Which of the following serotype of E.coli is the causative agent of hemorrhagic colitis?

Enterohemorrhagic E.coli O157:H7 is the serotype of E.coli causing hemorrhagic colitis. It is associated with the ingestion of undercooked hamburger, sprouts, unpasteurized milk or juice. EHEC produces a shiga toxin and can cause colitis after an incubation period of 3 -5 days. It typically produces watery diarrhea that progress to bloody diarrhea after a few hours to few days. Fatigue, abdominal pain, nausea and vomiting are associated complaints. Mechanism of enterohemorrhagic colitis appears to be vascular endothelial damage that leads to platelet aggregation and initiation of the coagulation cascade. This in turn, leads to ischemia of the colon and results in hemorrhagic colitis. Ref: Mayo Clinic Gastroenterology and Hepatology Board Review By Stephen Hauser, 4th Edition, Page 197