Contribution of stereochemical interactions in the adhesion of Streptococcus sanguis C5 to experimental pellicles

Parameters for the adsorption of Streptococcus sanguis C5 to experimental salivary pellicles were determined to assess the relative contributions of stereochemical and less specific hydrophobic-electrostatic interactions in this process. S. sanguis C5 cells possess hydrophobic surfaces and also an adhesin which exhibits stereochemical binding to sialic acid-containing salivary receptors. The adsorption of S. sanguis C5 to untreated pellicles was significantly better described by a two-site adsorption model than by a one-site model (p less than 0.001). One class of binding sites had an affinity for the organism that was more than 400 times that of the second class of binding sites. However, adsorption of the organism was better described by a one-site model to asialo pellicles prepared by neuraminidase treatment which destroyed the receptors for the organism's adhesin. The affinity of the organism to sites in asialo pellicles was low, and approximated that to the low-affinity sites in untreated pellicles. These observations suggest that, in the absence of stereochemical interactions involving the organism's adhesin and specific salivary receptors, S. sanguis C5 cells only exhibit low-affinity binding to experimental pellicles. This was substantiated by studies which showed that adsorption of the organism to albumin-coated hydroxyapatite and to polystyrene beads was also better described by a one-site model, and it occurred with only low affinity.