Hemolysin of Uropathogenic Escherichia coli Evokes Extensive Shedding of the Uroepithelium and Hemorrhage in Bladder Tissue Within the First 24 Hours After Intraurethral Inoculation of Mice

Department of Microbiology and Immunology, and Pathology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814-4799

^* To whom correspondence should be addressed. Email: aobrien{at}usuhs.mil.

	Abstract

Many uropathogenic Escherichia coli (UPEC) strains produce both hemolysin (Hly) and cytotoxic necrotizing factor type 1 (CNF1), and the loci for these toxins are often linked. That Hly and CNF1 contribute to urovirulence is supported by epidemiological studies associating the severity of urinary tract infections (UTIs) with toxin production by UPEC isolates. Additionally, we previously reported that mouse bladders and rat prostates infected with UPEC strain CP9 exhibit a more profound inflammatory response than do those organs from animals challenged with CP9cnf₁ and that CNF1 decreases antimicrobial activities of polymorphonuclear leukocytes. More recently, we created a Hly mutant, CP9hlyA₁::cat, and showed that it was less hemolytic and destructive for cultured bladder cells than was CP9. Here we evaluated the relative impact of mutations in hlyA₁ or cnf₁ alone or together on the pathogenicity of CP9 in a mouse model of ascending UTI. For that purpose, we constructed a hlyA₁ complemented clone of CP9hlyA₁::cat and a hlyA₁, cnf₁ CP9 double mutant. We found that Hly had no influence on bacterial colonization of the bladder or kidneys in single or mixed infections of wild-type and CP9hlyA₁::cat but that it did provoke sloughing of the uroepithelium and bladder hemorrhage within the first 24 hours after challenge. Finally, we confirmed that CNF1 expression induces bladder inflammation and in particular, as shown in this study, submucosal edema. From these data, we speculate that Hly and CNF1 may be largely responsible for the signs and symptoms of cystitis in humans infected with toxigenic UPEC.