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
Xanthogranulomatous pyelonephritis is most often due to? 
Select and explain. 
A. E. coli, B. Proteus, C. Pseudomonas, D. Klebsiella
B: Proteus
Answer: B: Proteus 
Explanation: .