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 a causative agent - 
Select and explain. 
A. O157:H7, B. O159:H7, C. O107:H7, D. O55:H7
A: O157:H7
Answer: A: O157:H7 
Explanation: Enterohemorrhagic E.coli dysentery can lead to complications like hemorrhagic uremic syndrome and hemorrhagic colitis.
Serotypes’ associated with EHEC are O157:H7 and O26:H1
Similar illness also produced by Shigella dysenteriae type1