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 the causative agent - 
Select and explain. 
A. 0 157 : H7, B. 0 159 : H7, C. 0 107 : H7, D. 0 55
A: 0 157 : H7
Answer: A: 0 157 : H7 
Explanation: Ans. is 'a' i.e., 0157 : 117