Streptococcus sanguis may play an important role in the initiation and maturation of dental plaque. These bacteria are among the first to colonize tooth surfaces by binding to components of the acquired salivary pellicle and serve in turn as binding sites for subsequent adherence of several other plaque bacteria. This interbacterial colonization is characteristic of the succession of bacterial adherence seen during plaque maturation. It has also been proposed that coherence of S. sanguis with black-pigmenting Bacteroides may permit these gram negative bacteria to colonize the oral cavity and ultimately the periodontal pocket. The long- range objective of this project is to characterize the coaggregation between S. sanguis and B. gingivalis and to define the modulating effects of human saliva and serum components on this phenomenon. Selected strains of S. sanguis and B. gingivalis (stock strains and fresh clinical isolates) will be tested for their coaggregating activities using visual and radioactivity assays. The effects of unfractionated saliva and serum samples on bacterial coaggregation will be studied in these assay systems. Components of saliva and serum that either inhibit or enhance coaggregation will be identified for further study. Specifically, host components that bind to surface structures of streptococci or bacteroides will be extracted from the cells with sodium dodecyl sulfate and identified by Western Blot assays using libraries of polyclonal and monoclonal reagents. The active component will then be isolated from saliva or serum using chromotographic procedures and analyzed for its activity on bacterial coaggregation. The structural domains of the salivary molecule which mediate coaggregation will be ascertained by studying the effects of reduction and alkylation, deglycosylation, delipidation, dephosphorylation, and proteolytic degradation. Finally, salivary composite molecules (subproject I.A.) will be assayed for modulation of streptococcal and Bacteroides coaggregation activity. We anticipate that the information from these studies could provide a rationale for selectivity regulating bacterial succession.