The Bacterial Connection between the Oral Cavity and the Gut Diseases

Abstract

More than 100 trillion symbiotic microorganisms constitutively colonize throughout the human body, including the oral cavity, the skin, and the gastrointestinal tract. The oral cavity harbors one of the most diverse and abundant microbial communities within the human body, second to the community that resides in the gastrointestinal tract, and is composed of >770 bacterial species. Advances in sequencing technologies help define the precise microbial landscape in our bodies. Environmental and functional differences render the composition of resident microbiota largely distinct between the mouth and the gut and lead to the development of unique microbial ecosystems in the 2 mucosal sites. However, it is apparent that there may be a microbial connection between these 2 mucosal sites in the context of disease pathogenesis. Accumulating evidence indicates that resident oral bacteria can translocate to the gastrointestinal tract through hematogenous and enteral routes. The dissemination of oral microbes to the gut may exacerbate various gastrointestinal diseases, including irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer. However, the precise role that oral microbes play in the extraoral organs, including the gut, remains elusive. Here, we review the recent findings on the dissemination of oral bacteria to the gastrointestinal tract and their possible contribution to the pathogenesis of gastrointestinal diseases. Although little is known about the mechanisms of ectopic colonization of the gut by oral bacteria, we also discuss the potential factors that allow the oral bacteria to colonize the gut.

The Oral Microbiome and Cancer

“…Finally, recent studies support the hypothesis that periodontal inflammation exacerbates gut inflammation in vivo by translocation of oral pathobionts to the gut, activating the inflammasome in colonic mononuclear phagocytes resulting in inflammation (221,222). Additionally, periodontitis results in the generation of reactive Th17 cells against oral bacteria.…”

Ectopic gut colonization: a metagenomic study of the oral and gut microbiome in Crohn’s disease

“…Crucially, this study found a cluster of CD subjects whose gut microbiome were characterized by S. salivarius , a prominent oral microbe. In health, Streptococcus genus typically constitute less than 4% of gut microbiome [ 13 ], thus it was note-worthy to find S. salivarius enriched in the gut microbiome of CD subjects. Although the ectopic colonization of oral bacteria such as Klebsiella pneumoniae has been found to induce intestinal inflammation and can result in the progression of CD [ 14 ], it was only demonstrated in mouse models.…”

“…Oral pathobiont-reactive inflammatory cells arising from oral inflammation were found to migrate to the gut, promoting and contributing to colitis [ 12 ]. The effect of the oral microbiome on CD is by comparison relatively understudied; however, its impact cannot be ignored [ 13 ]. A recent study found that oral Klebsiella can colonize the gut and result in severe gut inflammation in susceptible individuals, thereby exacerbating inflammatory disease [ 14 ].…”

Human oral microbiome dysbiosis as a novel non-invasive biomarker in detection of colorectal cancer

“…It was reported that oral bacterial diversity is higher in oral diseases, such as in periodontal disease 38 . By hematogenous and enteral routes, oral pathogenic bacteria can translocate to the gastrointestinal tract and induce various gastrointestinal diseases, which suggested that the higher diversity of oral microbiota in CRA group may be a high risk for gastrointestinal tumorigenesis 39 . Fusobacterium is known to be associated with colorectal adenomas and carcinoma 40 - 42 .…”