Experimental Escherichia coli epididymitis in rats:: a model to assess the outcome of antibiotic treatment

Objective To assess the effect of initial antimicrobial therapy with a new highly potent quinolone (sparfloxacin) on the outcome of infection, especially acute and chronic inflammation, in a rat model of unilateral Escherichia coli epididymitis. Materials and methods The study included 60 Sprague-Dawley rats, each of which received 0.1 ml, of an E. coli (0:6 strain) suspension (10(6) colony forming units/mL) injected into the right ductus deferens. At 24 h after infection an oral antimicrobial treatment with sparfloxacin was initiated in half of the animals. The rats were killed 14 days, 3 and 6 months after infection, and both epididymes and the prostate gland cultured to re-isolate E. coli. To evaluate the grade of inflammation in both epididymes, histological variables, including acute and chronic inflammation and scar formation, were evaluated and a total inflammatory score, representing the sum of all variables, computed. Results Whereas antimicrobial therapy eradicated the pathogen, in untreated animals the pathogen was detectable for up to 6 months after infection in the infected epididymis and/or the prostate gland, while the contralateral epididymis was sterile. The inflammatory reaction in the infected epididymis was significantly less in treated animals (P < 0.001). Subclinical nonbacterial inflammation was present in the contralateral epididymis. Conclusions Although adequate antimicrobial treatment eradicated the pathogen and reduced the grade of epididymal damage, inflammation was not avoided. Subclinical inflammation of the contralateral epididymis may contribute to impaired fertility. These results indicate that an inflammatory reaction initiated by bacteria might persist as a nonbacterial process despite early therapy, or by bacteria undetectable by conventional culture techniques, and may compromise male fertility.