Specific and Nonspecific Interactions between Salivary Proteins and Streptococcus mutans

Adhesion of proteins to natural surfaces, such as the bacterial cell wall, may be controlled by non-specific and/or specific interactions. The latter ones are mediated by adhesins on the (bacterial) surface. This paper reports on the interaction between saliva proteins and Streptococcus mutans, an oral bacterium that is involved in tooth decay, by comparing two strains of S. mutans, one with and one without the adhesin antigen I/II on its surface. Bacterium-saliva interaction is characterized in terms of enthalpy (calorimetry), strength of adhesive bond (AFM), affinity (adsorption isotherms), and kinetics of adhesion of the bacterial strains to a saliva-coated surface (parallel plate flow chamber). The study shows that the presence of antigen I/II at the streptococcal surface adds favorable binding sites that are biologically recognized by (a number of) salivary proteins. Thus, superimposed on generic interactions, specific pH-dependent short-range interactions contribute dominantly to the adhesion of antigen I/II containing S. mutans to salivary coatings, such as salivary conditioning films on tooth surfaces.