A simple model system was developed in order to study the effect of saliva on bacterial adhesion to a hydrophobic model surface, polystyrene. Washed bacterial suspensions of Acinetobacter calcoaceticus RAG-1 (ATCC 31012) and Serratia marcescens RZ were mixed with serial dilutions of clarified saliva, and the mixtures incubated in wells of untreated polystyrene microtiter plates. Adhesion was recorded spectrophotometrically after staining of adherent cells. Saliva inhibited adhesion of S. marcescens RZ in a concentration-dependent manner. Of interest was the finding that saliva exerts two distinct effects on adhesion of A. calcoaceticus RAG-1. It inhibits adhesion at low saliva concentrations, but causes aggregation of RAG-1 cells and stimulation of adhesion at high saliva concentrations. Extraction of saliva with hexadecane, prior to the adhesion assay, brought about an almost complete loss of the saliva-mediated inhibition of adhesion in both strains. This same treatment, however, did not prevent the aggregation of RAG-1 cells and the concomitant promotion of adhesion at high saliva concentrations. Initial evidence suggests that the components responsible for saliva-mediated inhibition of adhesion to polystyrene are of low (< 15 kD) molecular weight.
- Acinetobacter calcoaceticus
- Serratia marcescens