TYPE-1 FIMBRIAL EXPRESSION ENHANCES ESCHERICHIA-COLI VIRULENCE FOR THE URINARY-TRACT

Type 1 fimbriae are adhesion organelles expressed by many Gram-negativ e bacteria. They facilitate adherence to mucosal surfaces and inflamma tory cells in vitro, but their contribution to virulence has not been defined. This study presents evidence that type 1 fimbriae increase th e virulence of Escherichia coli for the urinary tract by promoting bac terial persistence and enhancing the inflammatory response to infectio n. In a clinical study, we observed that disease severity was greater in children infected with E. coli O1:K1:H7 isolates expressing type 1 fimbriae than in those infected with type 1 negative isolates of the s ame serotype. The E. coli O1:K1:H7 isolates had the same electrophoret ic type, were hemolysin-negative, expressed P fimbriae, and carried th e fim DNA sequences. When tested in a mouse urinary tract infection mo del, the type 1-positive E. coli O1:K1:H7 isolates survived in higher numbers, and induced a greater neutrophil influx into the urine, than O1:K1:H7 type 1-negative isolates. To confirm a role of type 1 fimbria e, a fimH null mutant (CN1016) was constructed from an O1:K1:H7 type 1 -positive parent. E. coli CN1016 had reduced survival and inflammatoge nicity in the mouse urinary tract infection model. E. coli CN1016 reco nstituted with type 1 fimbriae (E. coli CN1018) had restored virulence similar to that of the wild-type parent strain. These results show th at type 1 fimbriae in the genetic background of a uropathogenic strain contribute to the pathogenesis of E. coli in the urinary tract.