Increased adhesion of Enterococcus faecalis strains with bimodal electrophoretic mobility distributions

Initial adhesion is a determinant in the development of microbial biofilms. It is influenced, amongst others, by the surface hydrophobicity and the electrostatic characteristics of the substratum and adhering organisms. Enterococcus faecalis strains, grown in pure cultures, generally display subpopulations with different electrokinetic features, reflected in a bimodal electrophoretic mobility distribution. Here, the initial adhesion kinetics of five heterogeneous and five homogeneous E. faecalis strains were followed in a parallel-plate flow chamber. After 4h of flow, heterogeneous strains adhered in significantly higher numbers than homogeneous strains (7.3 x 10(6) and 1.9 x 10(6)cm(-2), respectively), but the initial deposition rates were not significantly influenced (740 and 600 cm(-2)s(-1), respectively). Apparently, initial deposition of bacteria is mainly governed by attractive Lifshitz-Van der Waals forces that overwhelm the electrostatic repulsion energy barrier, thus resulting in similar initial deposition rates for the various bacterial populations investigated. In contrast, during later stages of adhesion, bacteria in heterogeneous cultures likely experience a lower electrostatic repulsion from already adhering bacteria than bacteria in homogeneous cultures, thus allowing a closer proximity of the bacteria with respect to each other, which ultimately leads to increased adhesion after 4 h.