The MOST common organism isolated in emphysematous pyelonephritis is:

Emphysematous pyelonephritis is a form of acute necrotizing pyelonephritis secondary to a gas-producing bacteria (E coli in 66% of cases and Klebsiella in 26%). It is commonly seen in patients with poorly controlled diabetes (over 90% of cases) or in patients with upper urinary tract obstruction. The diagnosis is made by the usual signs of acute pyelonephritis and by the presence of gas in the renal collecting system and parenchyma seen on plain films, ultrasound, or CT. The condition is life threatening. Operative treatment, including nephrectomy and drainage along with antibiotics, decreases the moality rate. Ref: Cooper C.S., Joudi F.N., Williams R.D. (2010). Chapter 38. Urology. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.