Mutation of the gene encoding cytotoxic necrotizing factor type 1 (cnf(1))attenuates the virulence of uropathogenic Escherichia coli

Cytoxic necrotizing factor type 1 (CNF1) is a 115-kDa toxin that activates Rho GTPases and is produced by uropathogenic Escherichia coli (UPEC), While both epidemiological studies that link CNF1 production by E, coli with uri nary tract disease and the cytopathic effects of CNF1 on cultured urinary t ract cells are suggestive of a role for the toxin as a UPEC virulence facto r, few in vivo studies to test this possibility have been reported. Therefo re, in this investigation, we evaluated the importance of CNF1 in a murine model of urinary tract infection (UTI) by comparing the degree of colonizat ion and damage induced by three different CNF1-producing E, coli strains wi th isogenic CNF1-deficient derivatives. The data from single-strain challen ge experiments with C3H/HeOuJ mice indicated a trend toward higher counts o f the wild-type strains in the urine and bladders of these animals up to 3 days after challenge in two of three strain pairs. Furthermore, this differ ence was statistically significant at day 2 of infection with one strain pa ir, C189 and C189cnf(1). To control for the animal-to-animal variability in herent in this model, we infected C3H/HeOuJ mice with a mixture of CNF1-pos itive and -negative isogenic derivatives of CP9, The CNF1-positive strain w as recovered in higher numbers than the CNF1-negative strain in the urine, bladders, and kidneys of the mice up to 9 days postinfection, These strikin g coinfection findings, taken with the trends observed in single-strain inf ections, led us to conclude that CNF1-negative strains were generally atten uated compared to the wild type in the C3H/HeOuJ mouse model of UTI, Furthe rmore, histopathological examination of bladder specimens from mice infecte d with CNF1-positive strains consistently showed deeper, more extensive inf lammation than in those infected with the isogenic mutants. Lastly, we foun d that CNF1-positive strain CP9 was better able to resist kilting by fresh human neutrophils than were CP9crf(1) bacteria, From these data in aggregat e, we propose that CNF1 production increases the capacity of UPEC strains t o resist killing by neutrophils, which in turn permits these bacteria to ga in access to deeper tissue and persist better in the lower urinary tract.