Oral Microbiome: Potential Link to Systemic Diseases and Oral Cancer

Abstract

The human oral microbiome comprises more than 2,000 bacterial taxa, including a large number of opportunistic pathogens, and it is considered to be the second most diverse microbial community following stool. However, oral microbiome as a whole in determining human health and diseases has been understudied compared with the gut microbiome. Yet, potential links between oral bacteria and a range of systemic diseases have long been recognized based on their associations with periodontal diseases and surgical dental procedures. These pathological conditions include sepsis/endocarditis, cardiovascular diseases and their established risk factors, chronic kidney disease, Alzheimer's disease, rheumatoid arthritis, and head and neck cancer, and are reviewed here. Although local inflammation and physical interventions from dietary and hygiene habits can facilitate systemic dissemination of oral bacteria, studies have delineated several bacterial virulence factors from oral pathogens that are involved in systemic dissemination, inflammation, immune evasion, and cytotoxicities, and are thus relevant to systemic diseases. Unfortunately, mechanistic information to date has been primarily derived from a few periodontal pathogens. To fully elucidate host-microbial and microbial-microbial interactions pertinent to human health and disease, use of a multi-omics approach, including metagenomics, metabolomics, and transcriptomics, may be required.