Bacterial interactions and successions during plaque development

Oral populations shift from the low diversity found in initial communities of supragingival plaque to the high diversity present in mature communities in supragingival and subgingival plaque. Physical interactions among bacterial species, attachment to surfaces, and successive colonizations to form communities, are processes facilitated by coaggregation. Metabolic interactions among different bacterial cell types are likely to play a decisive role in the changes in community composition during plaque maturation. Co-operation among community members might facilitate nutrient availability and oxygen removal, favoring the proliferation of specific bacterial species. Diffusible small-molecule signals mediate communication among members of the same microcommunity: we propose that the concentration of these signals in the microcommunity is critical for the gene-regulation response by commensal and pathogenic organisms. Bacterial communities co-evolve with their human host and thus are host specific. Each human host has developed an inter-relationship with a specific set of bacterial species. The understanding of the factors that determine plaque maturation in that host is important, because the population shifts from predominantly gram-positive bacteria to obligately anaerobic gram-negative species. It remains unsolved as to how these shifts correlate with the appearance of gingivitis and, in the susceptible host, with the development of a periodontal lesion. Additional studies, involving natural mixed-species communities, confocal microscopy, signaling molecules, metabolic co-operation and antagonism, and molecular phylogenic analyses of culturable and yet-to-be cultured bacteria, are increasing our understanding of the biological and clinical processes involved in the development of plaque. © 2006 The Authors.