Oral microbial communities: Biofilms, interactions, and genetic systems

Oral microbial-plaque communities are biofilms composed of numerous genetic ally distinct types of bacteria that live in close juxtaposition on host su rfaces. These bacteria communicate through physical interactions called coa ggregation and coadhesion, as well as other physiological and metabolic int eractions. Streptococci and actinomyces are the major initial colonizers of the tooth surface, and the interactions between them and their substrata h elp establish the early biofilm community. Fusobacteria play a central role as physical bridges that mediate coaggregation of cells and as physiologic al bridges that promote anaerobic microenvironments which protect coaggrega ting strict anaerobes in an aerobic atmosphere. New technologies for invest igating bacterial populations with 16S rDNA probes have uncovered previousl y uncultured bacteria and have offered an approach to in situ examination o f the spatial arrangement of the participant cells in oral-plaque biofilms. Flow cells with saliva-coated surfaces are particularly useful for studies of biofilm formation and observation. The predicted sequential nature of c olonization of the tooth surface by members of different genera can be inve stigated by using these new technologies and imaging the cells in situ with confocal scanning laser microscopy. Members of at least seven genera now c an be subjected to genetic studies owing to the discovery of gene-transfer systems in these genera. Identification of contact-inducible genes in strep tococci offers an avenue to explore bacterial responses to their environmen t and leads the way toward understanding communication among inhabitants of a multispecies biofilm.