Affiliations: Pulp and Paper Research Institute of Canada, and Department of Chemistry, McGill University, Montreal, Quebec, Canada, H3A 2A7
Abstract: The adhesion of both live and fixed bacteria (Escherichia coli) on glass has been studied under well-defined hydrodynamic conditions, created in an impinging jet apparatus. With this technique one can accurately measure the initial deposition rate j0 on the surface, the average lifetime of a bacterium on the surface, τesc and the surface area blocked per deposited bacterium, normalized by its projected area, γ. The experimental results are compared to theoretical results for equivalent spheres. It is found that near the stagnation point the deposition rate j0 is mainly controlled by convective diffusive transport which, for rod-shaped Escherichia coli, with an axis ratio of about 2, is found to be equal to that for spheres. No differences in j0 and τesc were found between live and fixed bacteria at low flow rates. At high flow rates fixed bacteria adhered to the surface at a slower rate. In both systems j0 was found to decrease suddenly at a distance of about 150 μm from the stagnation point, in contrast to systems of spherical particles for which j0 is uniform over the surface. Most likely this is due to the rotation of the rod-shaped particles, which vary their distance to the surface periodically with time. The main difference between live and fixed bacteria, besides different deposition rates in strong flows, is that γ is about 30% larger for fixed bacteria than for live ones, resulting in a much lower final coverage for fixed bacteria. These results imply a larger repulsion between fixed bacteria than between living ones. From detachment experiments we can conclude that not all bacteria stick to the surface with the same bond strength. The variation in the bond strength is due to the aging of the bonds between the bacteria and the surface. The average bond strength corresponds to an energy of about 13-15 kT.
