<prompt> Xanthogranulomatous pyelonephritis is most often due toE. coliProteusPseudomonasKlebsiella  <response>: 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 