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: Surgery
Xanthogranulomatous pyelonephritis is often associated with infection by 
Select and explain. 
A. Proteus, B. E. coli, C. S. aureus, D. Klebsiella
A: Proteus
Answer: A: Proteus 
Explanation: None