Bacteremia in the pathogenesis of retrograde E. coli pyelonephritis in the rat

Female rats deprived of water overnight, and then given 1.0 ml of E coli 0111:B4 via the urethra, developed pyelonephritis. A nearly absolute association was found between the occurrence of bacteremia after the transurethral infusion and the development of pyelonephritis. An identical lesion was produced by a combination of forniceal damage and intravenous injection of E coli. The kidney damaged by reflux was shown to be more susceptible to hematogenous pyelonephritis than the obstructed kidney and the distribution of the infection was due to localization of bacteria in the damaged fornix but not to the route of infection. The induction of retrograde E coli pyelonephritis in the rat required a tear in the pelvic epithelium creating pyelovenous communications, and the resultant bacteremia produced pyelonephritis. The incidence of ureteral reflux and the volume of inoculum that refluxed to the renal pelvis was shown radiologically to be a function of bladder distensibility, which is reduced by withholding water for a few hours. In this system, retrograde E coli pyelonephritis developed from a combination of two factors: (1) reflux-induced damage to the renal pelvis so that E coli are introduced into the kidney and (2) hematogenous infection of the damaged kidney.