Microbial protection and virulence in periodontal tissue as a function of polymicrobial communities: symbiosis and dysbiosis.

This review discusses polymicrobial interactions with the host in both health and disease. As our ability to identify specific bacterial clonal types, with respect to their abundance and location in the oral biofilm, improves, we will learn more concerning their contribution to both oral health and disease. Recent studies examining host- bacteria interactions have revealed that commensal bacteria not only protect the host simply by niche occupation, but that bacterial interactions with host tissue can promote the development of proper tissue structure and function. These data indicate that our host-associated polymicrobial communities, such as those found in the oral cavity, co-evolved with us and have become an integral part of who we are. Understanding the microbial community factors that underpin the associations with host tissue that contribute to periodontal health may also reveal how dysbiotic periodontopathic oral communities disrupt normal periodontal tissue functions in disease. A disruption of the oral microbial community creates dysbiosis, either by overgrowth of specific or nonspecific microorganisms or by changes in the local host response where the community can now support a disease state. Dysbiosis provides the link between systemic changes (e.g. diabetes) and exogenous risk factors (e.g. smoking), and the dysbiotic community, and can drive the destruction of periodontal tissue. Many other risk factors associated with periodontal disease, such as stress, aging and genetics, are also likely to affect the microbial community, and more research is needed, utilizing sophisticated bacterial taxonomic techniques, to elucidate these effects on the microbiome and to develop strategies to target the dysbiotic mechanisms and improve periodontal health.