Although Streptoccus sanguis is among the earliest colonizers of dental plaque, the molecular basis for its affinity for tooth surfaces is still not well understood. A number of laboratories have shown that this species as a high affinity for salivary glycoproteins which form the primary coating on the tooth surface. In addition, other studies indicate that S. sanguis can aggregate with salivary glycoproteins. These aggregates are believed to play a major role in controlling the numbers of bacteria in the oral cavity. Although both kinds of interactions appear to be specific, the molecular basis of these reactions is not known. We have been attempting to dissect the surface of S. sanguis and determine the specific molecules involved in each phenomenon. An adhesion assay which utilizes saliva coated hydroxyapatite has been shown to mimic the adhesion of S. sanguis to salivary pellicles. The saliva mediated aggregation assay employs both turbidimetric and sucrose gradients to determine the degree of bacterial aggregation. The surface of S. sanguis is much more complex than generally assumed. More than nine surface proteins always appear to be present in autoradiographs of iodinated cells. The surface antigenic composition also shows a complex surface. Attempts have been made to define the surface adhesions using chemostat cultures and a non-adherent mutant to determine if particular surface antigens were associated with adhesion. Although the results suggest such relationshps were present, the complexity of the surface made it difficult to isolate the antigens involved. Shotgun cloning methods will be used to introduce genes for specific surface antigens into E. coli; the antigens will be isolated and purified. Using these antigens, it will be possible to establish their relationship to adhesion and aggregation more directly. Monoclonal antibodies will also be produced to use both as markers for these antigens and as reagents which can help to purify them. The results of these studies could provide the basis for the preparation of chemotherapeutic agents or vaccines which could prevent plaque formation.