Vesicoureteral reflux induces renal trauma in a mouse model of ascending, unobstructed pyelonephritis

To determine whether in a mouse model of ascending, unobstructed urinary tract infection an inoculum volume could be found that induces vesicoureteral reflux without causing renal injury, the occurrence of vesicoureteral reflux (identified by inspection, kidney culture, and histopathologic examination) was compared with the occurrence of renal trauma (identified by histopathologic examination and cultures of blood and spleen) in female Swiss Webster mice after transurethral inoculation with 50, 75, 100 or 150 μl. of a bacterial suspension containing India ink. Vesicoureteral reflux (which was more common the greater the inoculum volume) induced renal trauma even with small (50 μl.) inoculum volumes, accounting for the observed association of inoculum volume and renal injury. No single parameter of vesicoureteral reflux identified all refluxed or traumatized kidneys. Thus, careful attention to the avoidance of vesicoureteral reflux following inoculation, using multiple indicators of reflux, is needed if this model is to faithfully reproduce infections occurring in the nontraumatized human urinary tract.