Prelude to oral microbes and chronic diseases: past, present and future

Abstract

Associations between oral and systemic health are ancient. Oral opportunistic bacteria, particularly, Porphyromonas gingivalis and Fusobacterium nucleatum, have recently been deviated from their traditional roles as periodontal pathogens and arguably ascended to central players based on their participations in complex co-dependent mechanisms of diverse systemic chronic diseases risk and pathogenesis, including cancers, rheumatoid-arthritis, and diabetes.

Keywords: Cancer; Chronic diseases; Fusobacterium nucleatum; Oral microbes; Porphyromonas gingivalis; Small molecule danger signaling.

Diagram 1. Postulated Relationships of Oral Microbes to Diverse Chronic Diseases

The oral microbiome and specific subset of pathogens, in particular, Porphyromonas gingivalis and a few others, have been suggested to play an important role in multiple anatomically and clinically unrelated chronic diseases such as periodontal disease, orodigestive and gastrointestinal cancers, rheumatoid arthritis, and diabetes. P. gingivalis, a key-stone pathogen, has been implicated in all these chronic diseases, whereas other oral microbes have been associated only with some of these conditions. The driving processes of these diseases appear to involve multifaceted complex interactions among the oral microbiome constituents, the host genetic, immunological behavioral factors, and environmental conditions working in concert to shape a local microenvironment that predisposes the host cells to inflammation, transformation and promotes the development and/or progression of these diseases. It is tempting to extrapolate the common pathways that seem to be shared among the etiologies of all these diseases, and which seem to be influenced by the microbiome. Thus the specific microbiome and host components can be disease inducers and may act as important risk modifiers and early diagnostic/prognostic factors for the management of these diseases. We accordingly call those potentially major disease determinants as ‘danger profiles or signatures’.