In the human body, organisms that originate from a specific location or organ in the body have their activities being done to benefit the particular location or organ. These organisms are referred to as normal flora.

Nonetheless, these very helpful organisms can migrate from their original home and invade other places of the body. When these migrating organisms successfully colonise a different location in the human body, their once helpful activities tend to rather cause harm in the new location and destabilise the balance in that place and the same phenomenon occurs with the oral microbeum and the other parts of the body.

When these oral microbeum leave their natural home in the mouth and invade other places in the human body, their activities in the new place tend to cause a lot of harm instead of the helpful benefits.

Recent studies have shown that oral-derived bacteria can colonize the intestines and persist there, leading to activation of the intestinal immune system and chronic inflammation [1]. Eventually, giving rise to a list of disease conditions.

The immune system is programmed in such a way to react to anything it considers as a foreign body/substance. And oral microorganisms being found in any part of the body aside the mouth is a threat to the overall health and balance of the individual person and as such, the immune system is triggered to respond to that invasion.

Although many studies have confirmed the close correlation between oral micro bacteria and digestive diseases, the physiological distance between the oral cavity and lower digestive system cannot be ignored. To explain this distance, three ways have been proposed to be the main reason behind the oral microbes ability to migrate and gain access into the lower digestive system. The suggested three ways are explained below.

1) The oral microbacterium directly invades the intestinal tract through the esophagus, causing an imbalance in the intestinal micro-ecology and affecting the digestive system [[2], [3], [4], [5]]. This theory suggests that, throwing swallowing and other such activities, the oral bacterium swallowed are able to successfully enter the lower digestive system and begin their invasive activities.

2) Oral microorganisms, especially pathogenic bacteria of periodontitis, can enter the systemic circulation through the periodontal blood, thereby acting on the whole body [6]. This explains that, oral microbacterium can gain access into the blood circulation through the oral blood vessels. This can occur through mouth bleeds, mouth ulcers and conditions that expose the blood vessels to oral microbacterium.

3) The metabolites of oral microbiota enter the bloodstream and the systemic circulation, so that the human body is in a low-grade inflammatory state. The development of various chronic diseases of the digestive system is then promoted. Although this approach is currently not supported by direct evidence from oral microbiological studies, it has been confirmed in studies on gut microbiota imbalance leading to systemic disease. Therefore, this pathway may also be an important way for oral microbiota to act on digestive diseases [[7], [8], [9]]

From this, it is quite obvious the impact oral bacterium can have on the overall health of an individual. From oral conditions such as periodontitis, dental caries, etc to chronic diseases like diabetes, IBD, heart disease, etc.

References

1. E.M. du Teil, G. Gabarrini, H. Harmsen, J. Westra, A.J. van Winkelhoff, J.M. van Dijl
Talk to your gut: the oral-gut microbiome axis and its immunomodulatory role in the etiology of rheumatoid arthritis
FEMS Microbiol. Rev. (2018)

2. N. Qin, F. Yang, A. Li, E. Prifti, Y. Chen, L. Shao, J. Guo, E. Le Chatelier, J. Yao, L. Wu, J. Zhou, S. Ni, L. Liu, N. Pons, J.M. Batto, S.P. Kennedy, P. Leonard, C. Yuan, W. Ding, Y. Chen, X. Hu, B. Zheng, G. Qian, W. Xu, S.D. Ehrlich, S. Zheng, L. Li
Alterations of the human gut microbiome in liver cirrhosis
Nature, 513 (7516) (2014), pp. 59-64

3. M. Nakajima, K. Arimatsu, T. Kato, Y. Matsuda, T. Minagawa, N. Takahashi, H. Ohno, K. Yamazaki
Oral administration of P. Gingivalis induces dysbiosis of gut microbiota and impaired barrier function leading to dissemination of Enterobacteria to the liver
PLoS One, 10 (07) (2015), Article e0134234

4. K. Arimatsu, H. Yamada, H. Miyazawa, T. Minagawa, M. Nakajima, M.I. Ryder, K. Gotoh, D. Motooka, S. Nakamura, T. Iida, K. Yamazaki
Oral pathobiont induces systemic inflammation and metabolic changes associated with alteration of gut microbiota
Sci. Rep., 4 (2014), p. 4828

5. M. Nakajima, K. Arimatsu, T. Kato, Y. Matsuda, T. Minagawa, N. Takahashi, H. Ohno, K. Yamazaki
Oral administration of P. Gingivalis induces dysbiosis of gut microbiota and impaired barrier function leading to dissemination of Enterobacteria to the liver
PLoS One, 10 (7) (2015), Article e0134234

6. J. Abed, J.E. Emgard, G. Zamir, M. Faroja, G. Almogy, A. Grenov, A. Sol, R. Naor, E. Pikarsky, K.A. Atlan, A. Mellul, S. Chaushu, A.L. Manson, A.M. Earl, N. Ou, C.A. Brennan, W.S. Garrett, G. Bachrach
Fap2 mediates Fusobacterium nucleatum colorectal adenocarcinoma enrichment by binding to tumor-expressed Gal-GalNAc
Cell Host Microbe, 20 (2) (2016), pp. 215-225

7. J.C. Clemente, J. Manasson, J.U. Scher
The role of the gut microbiome in systemic inflammatory disease BMJ, 360 (2018), p. j5145

8. J.M. Pickard, M.Y. Zeng, R. Caruso, G. Nunez
Gut microbiota: role in pathogen colonization, immune responses, and inflammatory disease
Immunol. Rev., 279 (1) (2017), pp. 70-89

9. N. Kamada, S.U. Seo, G.Y. Chen, G. Nunez
Role of the gut microbiota in immunity and inflammatory disease Nat. Rev. Immunol., 13 (5) (2013), pp. 321-335