Biofilm formation in a hydrodynamic environment by novel FimH variants andramifications for virulence

Type 1 fimbriae are surface-located adhesion organelles of Escherichia coli that are directly associated with virulence of the urinary tract. They med iate D-mannose-sensitive binding to different host surfaces by way of the m inor fimbrial component FimH. Naturally occurring variants of FimH that bin d strongly to terminally exposed monomannose residues have been associated with a pathogenicity-adaptive phenotype that enhances E. coli colonization of extraintestinal locations such as the urinary tract. The FimH adhesin al so promotes biofilm formation in a mannose-inhibitable manner on abiotic su rfaces under static growth conditions. In this study, we used random mutage nesis combined with a novel selection-enrichment technique to specifically identify mutations in the FimH adhesin that confer on E. coli the ability t o form biofilms under hydrodynamic flow (HDF) conditions. We identified thr ee FimH variants from our mutant library that could mediate an HDF biofilm formation phenotype to various degrees. This phenotype was induced by the c umulative effect of multiple Changes throughout the receptor binding region of the protein. Two of the HDF biofilm-forming FimH variants were insensit ive to mannose inhibition and represent novel phenotypes not previously ide ntified in naturally occurring isolates. Characterization of our enriched c lones revealed some similarities to amino acid alterations that occur in ur inary tract infection (UTI) strains. Subsequent screening of a selection of UTI FimH variants demonstrated that they too could promote biofilm formati on on abiotic surfaces under HDF conditions. Interestingly, the same correl ation was not observed for commensal FimH variants. FimH is a multifaceted protein prone to rapid microevolution. In addition to its previously docume nted roles in adherence and invasion, we have now demonstrated its function in biofilm formation on abiotic surfaces subjected to HDF conditions. The study indicates that UTI FimH variants possess adaptations that enhance bio film formation and suggests a novel role for FimH in UTIs associated with m edical implants such as catheters.