LOCALIZATION OF A DOMAIN IN THE FIMH ADHESIN OF ESCHERICHIA-COLI TYPE-1 FIMBRIAE CAPABLE OF RECEPTOR RECOGNITION AND USE OF A DOMAIN-SPECIFIC ANTIBODY TO CONFER PROTECTION AGAINST EXPERIMENTAL URINARY-TRACT INFECTION

The FimH subunit of type 1-fimbriated Escherichia coli has been implic ated as an important determinant of bacterial adherence and colonizati on of the urinary tract. Here, we sought to localize the functionally important domain(s) within the FimH molecule and to determine if antib odies against this domain would block adherence of type 1-fimbriated E . coli to the bladder mucosa in situ and in vivo in an established mou se model of cystitis. We generated translational fusion proteins of di sparate regions of the FimH molecule with an affinity tag MalE, and te sted each of the fusion products in vitro for functional activity. The minimum region responsible for binding mouse bladder epithelial cells and a soluble mannoprotein, horseradish peroxidase, was contained wit hin residues 1-100 of the FimH molecule. We validated and extended the se findings by demonstrating that antibodies directed at the putative binding region of FimH or at synthetic peptides corresponding to epito pes within the binding domain could specifically block type 1 fimbriae -mediated bacterial adherence to bladder epithelial cells in situ and yeast cells in vitro. Next, we compared the ability of mice passively immunized intraperitoneally with antisera raised against residues 1-25 and 253-264 of FimH or 1-13 of FimA to resist bladder colonization in vivo after intravesicular challenge with type 1-fimbriated E. coli. O nly the antibody directed at the putative binding region of FimH (anti -s-FimH(1-25)) significantly reduced E. coli bladder infections in the experimental mouse model of urinary tract infections. Similar results were obtained when the mice were actively immunized with synthetic pe ptides corresponding to residues 1-25 and 253-264 of FimH or 1-13 of F imA. The mechanism of protection was attributed, at least in part, to inhibition of bacterial adherence to the bladder surface by s-FimH(1-2 5)-specific antibody molecules that had filtered through the kidneys i nto the urine. The level of FimH antibodies entering the bladder from the circulatory system of the immunized mice was found to be markedly enhanced upon bacterial challenge. The potential broad spectrum activi ty of the protective FimH antibody was indicated from its serologic cr oss-reactivity with various urinary tract bacterial isolates bearing t ype 1 fimbriae. These findings could be relevant in the design of an e fficacious and broadly reactive FimH vaccine against urinary tract inf ections.