Adhesion of Actinobacillus actinomycetemcomitans to a human oral cell line

Two quantitative, rapid assays were developed to study the adhesion of Actinobacillus actinomycetemcomitans, an oral bacterium associated with periodontal disease, to human epithelial cells. The human oral carcinoma cell line KB was grown in microtiter plates, and adherent bacteria were detected by an enzyme-linked immunosorbent assay with purified anti-A. actinomycetemcomitans serum and horseradish peroxidase-conjugated secondary antibody or [3H]thymidine-labeled bacteria. Adhesion was found to be time dependent and increased linearly with increasing numbers of bacteria added. Variation in the level of adhesion was noted among strains of A. actinomycetemcomitans. Adhesion was not significantly altered by changes in pH (from pH 5 to 9) but was sensitive to sodium chloride concentrations greater than 0.15 M. Pooled human saliva was inhibitory for adhesion when bacteria were pretreated with saliva before being added to the cells. Pretreatment of the KB cells with saliva did not inhibit adhesion. Protease treatment of A. actinomycetemcomitans reduced adhesion of the bacteria to KB cells. The data are consistent with the hypothesis that a protein(s) is required for bacterial adhesion and that host components may play a role in modulating adhesion to epithelial cells.