Bacterial interactions in periodontal diseases

The oral cavity comprises a vast number of different bacterial populations which constitute a perfect example of microbial ecology. Bacterial species present in the various oral sites normally coexist harmoniously. However, u nder specific conditions which favour some species with pathogenic potentia l over the other members of the community, periodontal diseases are initiat ed. On the one hand, bacterial interactions both positive (mutualism, comme nsalism and synergism) and negative (competition and antagonism) may play a significant role in these mixed infections by ultimately favouring the per iodontopathogenic species. On the other hand, certain types of bacterial in teractions may help maintain a healthy state by preventing colonization of subgingival sites by pathogenic species. This review will focus on positive and negative bacterial interactions involving the principal periodontopath ogens : Porphyromonas gingivalis, Treponema denticola, Bacteroides forsythu s and Actinobacillus actinomycetemcomitans.