Biofilm Formation in a Hydrodynamic Environment by Novel FimH Variants and Ramifications for Virulence

Abstract

Type 1 fimbriae are surface-located adhesion organelles of Escherichia coli that are directly associated with virulence of the urinary tract. They mediate D-mannose-sensitive binding to different host surfaces by way of the minor fimbrial component FimH. Naturally occurring variants of FimH that bind 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 also promotes biofilm formation in a mannose-inhibitable manner on abiotic surfaces under static growth conditions. In this study, we used random mutagenesis combined with a novel selection-enrichment technique to specifically identify mutations in the FimH adhesin that confer on E. coli the ability to form biofilms under hydrodynamic flow (HDF) conditions. We identified three FimH variants from our mutant library that could mediate an HDF biofilm formation phenotype to various degrees. This phenotype was induced by the cumulative effect of multiple changes throughout the receptor-binding region of the protein. Two of the HDF biofilm-forming FimH variants were insensitive to mannose inhibition and represent novel phenotypes not previously identified in naturally occurring isolates. Characterization of our enriched clones revealed some similarities to amino acid alterations that occur in urinary tract infection (UTI) strains. Subsequent screening of a selection of UTI FimH variants demonstrated that they too could promote biofilm formation on abiotic surfaces under HDF conditions. Interestingly, the same correlation was not observed for commensal FimH variants. FimH is a multifaceted protein prone to rapid microevolution. In addition to its previously documented 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 biofilm formation and suggests a novel role for FimH in UTIs associated with medical implants such as catheters.

Klebsiella pneumoniae: Going on the Offense with a Strong Defense

“…The precise role of type 1 fimbriae in the production of biofilms by K. pneumoniae is not as clear. While one report found that type 1 fimbriae promoted K. pneumoniae biofilm formation on abiotic surfaces in a role reminiscent of that played by the homologous FimH protein in biofilm production by E. coli, another study found that type 1 fimbriae were downregulated in biofilm cells and did not influence biofilm formation (117,295,297,298).…”

PslG, a self-produced glycosyl hydrolase, triggers biofilm disassembly by disrupting exopolysaccharide matrix

“…Biofilms of P. syringae and P. stutzeri were grown at 30 ºC in K medium [49]. M9 medium was used to grow the biofilm of E. coli at 37 ºC [50]. Biofilm of S. aureus was grown at 37 ºC in tryptic soy broth (TSB; Becton Dickinson) with 0.25% glucose [51]; Biofilm of C. albicans was grown in Lee's medium at 25 °C [52]; Biofilm of S. enteric was grown at 28 ºC in LB broth [53].…”

Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

“…et al (1986) Fimbriae-mediated adherence is important for the virulence of uropathogenic E. coli (UPEC), and the expression of type 1 fimbriae is linked to urinary tract colonization and pathogenesis (Connell et al, 1996;Martinez et al, 2000;Mulvey, 2002). Type 1 fimbriae have also been described as key factors in biofilm establishment on abiotic surfaces (Pratt & Kolter, 1998;Schembri & Klemm, 2001). Under static growth conditions, type 1 fimbriae provide stable interactions between bacteria and different surfaces, including polystyrene, PVC, polycarbonate and borosilicate glass -a prerequisite for biofilm formation.…”