Induction of Urinary Tract Infection by Intraurethral Inoculation with Escherichia coli: Refining the Murine Model

Murine models are important for studying the induction and pathophysiology of ascending urinary tract infections (UTI). However, when vesicoureteral reflux occurs during intravesical inoculation of mice with bacterial suspensions, it is difficult to distinguish between naturally ascending infections and those resulting from the inoculation procedure. The current study investigated whether introducing a bacterial suspension into the urethra rather than into the bladder could minimize or eliminate this complication. There were no differences in the intensity or time course of bladder infections induced byintraurethral or intravesical inoculation. In contrast, the prevalence of kidney infections was < 7% in mice given 10 µL of intraurethral inoculations versus nearly 60% in animals inoculated intravesically with 100 µL. There were equivalent numbers of bacteria in the kidneys after inoculation by either route. Thus, intraurethral inoculation of female mice with a small volume of bacteria appears to simulate most closely the pathophysiology of ascending UTIs in humans.