Ureaplasma urealyticum upper urinary tract infection: persistence and pathogenicity in a canine model

Ureaplasma urealyticum is an opportunistic pathogen, commonly isolated from the lower urogenital tract. Although U. urealyticum has been cultured from the upper urinary tracts of patients with interstitial renal diseases and struvite renal calculi, the precise role of ureaplasmas in upper tract diseases is unknown. To evaluate their potential significance in the etiology of renal diseases, we studied survival, multiplication, and pathogenicity of U. urealyticum in canine kidneys with experimentally induced hydronephrosis. After inoculation of the prototypic serovar (Type 8, strain 960) of U. urealyticum, seral urine specimens were obtained using a subcutaneously positioned nephrostomy catheter. Although U. urealyticum survived for less than 48 hours in canine urine in vitro, organisms persisted in the obstructed upper urinary tract for at least 21 days. Urinary pH of infected renal units increased to 7.5 to 8.5, a most unfavorable range for U. urealyticum in culture. Renal parenchyma had higher concentrations of ureaplasmas (8.7 X 10(3) to 9.5 X 10(4) CFU/gm.) than either renal pelvis tissue (1.0 X 10(3) CFU/gm.) or urine (6.5 X 10(3) CFU/ml.). Histologic studies demonstrated progressive interstitial inflammation in infected kidneys but similar changes were not apparent in obstructed, uninfected kidneys. The obstructed upper urinary tract appears to provide favorable conditions for ureaplasmas which may cause progressive interstitial inflammation in the absence of other pathogens.