The role of type 1 fimbriae in adhesion of Escherichia coli to hydrophilic and hydrophobic surfaces

Adhesion of two different Escherichia coli strains and their respective isogenic fimbriated and non-fimbriated mutants to hydrophilic, hydrophobic and wettability gradient surfaces was studied with respect to the expression of type 1 fimbriae and cell surface characters. Generally, initial adhesion of fimbriated strains was lower than for non-fimbriated strains. However, after an additional 1 h of incubation, the relative distribution of firmly attached cells on wettability gradient surfaces showed that adhesion of fimbriated strains was high on the hydrophobic part and low on the hydrophilic part of the gradient while non-fimbriated strains showed an opposite relationship. Moreover, on hydrophobic surfaces the strength of adhesion was enhanced by fimbriae as assessed by exposing attached bacteria to 0.04% sodium dodecyl sulphate (SDS). Purified fimbriae also adsorbed more and stronger to hydrophobic surfaces than to hydrophilic surfaces. Our results suggest that fimbriae do not facilitate the initial contact of bacterial cells to a surface, but contribute to increased subsequent interaction of bacteria with hydrophobic surfaces due to a higher cell surface hydrophobicity, a lower electrokinetic potential, and possibly by increased interactions through conformational changes of type 1 fimbriae on the surface. On hydrophilic surfaces, however, type 1 fimbriae may have an adverse effect and hinder cells from firm adhesion.