This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
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: Xanthogranulomatous pyelonephritis occurs when a chronic urinary obstruction (often by staghorn calculi), together with chronic infection, leads to the suppurative destruction of renal tissue.Proteus infection is associated with staghorn formation.Ref: Harrison; 19th edition; Page no: 1033