This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
A 20 year old man presented with hemorrhagic colitis. The stool sample grew Escherichia coli in pure culture. The following serotype of E.coli is likely to be causative agent - 
Select and explain. 
A. 0157:H7, B. 0 159:H7, C. 0107:H7, D. 0 55:H7
A: 0157:H7
Answer: A: 0157:H7 
Explanation: Ans. is 'a' i.e., 0 157 : H7 . Amongst E. coli, Enterohemorrhagic E. coli causes heamorrhagic colitis and the typical EHEC is serotype 0157: H7. Remember . Few other serotype such as 026 : Hl also belongs to this category.