This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
[{'content': 'Xanthogranulomatous pyelonephritis is most often due to? \nSelect and explain. \nA. E. coli, B. Proteus, C. Pseudomonas, D. Klebsiella', 'role': 'user'}, {'content': 'Answer: B \nExplanation: .', 'role': 'assistant'}]