Adsorption of salivary proteins to the surface of oral streptococcal cells.

Oral tissues, especially tooth surfaces, are covered with a layer of salivary proteins. Oral bacterial cells that adsorb to salivary components accumulated on the tooth surface are, as a rule, covered with the same components, especially proteins. Thus, it is possible that the salivary proteins covering the bacterial cells are related to the adhesion of bacteria to oral tissues. The aim of this study was to clarify the mechanisms of adsorption of salivary proteins to the surface of Streptococcus sanguis, S. mitis and S. salivarius using an adsorption assay with salivary proteins labeled with tritiated formaldehyde. The results showed that salivary proteins adsorbed more to S. salivarius than to S. mitis, and least to S. sanguis. It was evident that hydrophobic bonding was involved in the adsorption of salivary proteins to the bacterial cells tested. The amount of salivary proteins adsorbed to S. mitis and S. salivarius was decreased by the presence of phosphate, that to S. sanguis was increased by the presence of a divalent cation such as Ca2+, and that to all bacteria tested was inhibited in different ways by the presence of sugars. The amount of salivary proteins adsorbed to S. sanguis and S. salivarius was reduced effectively by pretreatment of the cells with trypsin, chymotrypsin and papain. In the case of S. mitis, the amount of adsorbed salivary proteins was decreased by pretreatment of the cells with chymotrypsin only, and was increased by pretreatment with lipase. These results indicate that there are different mechanisms of adsorption of salivary protein to the cell surfaces of oral streptococci.