Shear-enhanced oral microbial adhesion

Abstract

Shear-enhanced adhesion, although not observed for fimbria-mediated adhesion of oral Actinomyces spp., was noted for Hsa-mediated adhesion of Streptococcus gordonii to sialic acid-containing receptors, an interaction implicated in the pathogenesis of infective endocarditis.

FIG. 1.

Dynamic adhesion experiment with A. oris T14V bearing type 1 and type 2 fimbriae (1⁺2⁺), A. naeslundii WVU45 bearing type 2 fimbriae (2⁺), or different fimbria-deficient mutants (fimbria production in parentheses) on glass coated with 25% saliva (A), 5 μg/ml PRP-1 (B), or 25 μg/ml asialofetuin (C). Cell suspensions were pumped into channels of a Bioflux 100 plate, and after a 5-min adherence period at 5 Pa, the shear force was decreased over sequential 5-min intervals to 2.5, 1, 0.5, 0.1, 0.05, and 0 Pa (i.e., no flow). Mean values for total cells bound (rolling plus stationary; filled bars, rolling cells; open bars, stationary cells) and exact 95% confidence intervals for a Poisson variable were calculated from six repetitions. Adherence was recorded only upon application of shear force after flow had reached 0, after which shear was increased stepwise as in shear-enhanced experiments. The values shown are those recorded at the system's highest shear force (5 Pa); the number of cells bound as well as the fraction of stationary cells remained essentially the same for each strain regardless of shear force, i.e., neither typical dynamic adhesion nor shear-enhanced adhesion was seen.

FIG. 2.

(A) Dynamic adhesion of wild-type S. gordonii DL1 to glass coated with different concentrations of fetuin or 25% saliva. Cell suspensions of this strain or the Hsa-deficient mutant strain D102 were pumped through channels of a Bioflux 100 plate at flow rates corresponding to shear forces ranging from 5 to 0.01 Pa. Total cells (i.e., rolling plus stationary) bound per field of view were determined after 5 min at each shear force. Mean values for cells bound per field of view and exact 95% confidence intervals for a Poisson variable were calculated from six repetitions. (B) Shear-enhanced adhesion of S. gordonii DL1. Cell suspensions were pumped through channels of a Bioflux 100 plate at a shear force of 0.01 Pa for 5 min to allow accumulation of bound cells as in panel A. Shear force was then set at a value ranging from 0.01 to 5 Pa, as indicated on the logarithmic x axis. After 5 min at each shear force, the fraction of stationary cells was determined by counting stationary and rolling cells. Mean values for the fraction of stationary cells and exact 95% confidence intervals for a binomial distribution were calculated from 10 repetitions.

FIG. 3.

Reversible nature of S. gordonii DL1 shear-enhanced adhesion to glass coated with 25 μg/ml fetuin. Cell suspensions were pumped through channels of a Bioflux 100 plate at a shear force of 0.01 Pa for 5 min to allow accumulation of approximately 150 total cells per field of view. Shear force was then increased to 0.05 Pa for 60 s, increased to 2.5 Pa for another 60 s, and then decreased to 0.05 Pa for 60 s. During each time, the number of total cells bound remained constant. The fraction of stationary cells was determined by continuous counting of both stationary and rolling cells.