The Origin Story Behind Our Oral Microbiome
Each of us has a unique oral microbiome, or collection of microorganisms inhabiting our oral cavities. What remains something of a mystery are the factors that influence its composition. Read on for some insights into what researchers know when it comes to the source of our mouth microbiota.
The genesis of our oral microbiomes
Whether babies are born with oral microbiota is still up for debate 1. However, researchers do know that after being exposed to bacteria through contact with their mother’s body or from feeding, their tongue and cheek cells become home to the primary or first colonizers. Then, once the teeth erupt, additional microorganisms join the party, adhering to this new surface or to each other. Once the teeth erupt, babies’ oral microbiomes diverge more from those of their mothers.
The factors behind their initial makeup
Although the exact sources of microbiota are still unknown, researchers realize that contact with mothers’ bodies plays a key role. According to a 2018 study, scientists found that in 85% of infants, the composition of their oral microbiome was like that of their mothers’.2 Plus, according to a different 2018 study, the bacteria present differed depending on whether babies were born vaginally or via C-section, showing that at least some primary colonizers come from exposure to the mother’s body.3
Some researchers, like the authors of a recent Nature article, believe genetics also plays a role in the oral microbiome’s initial makeup.4 However, others, like the authors of a 2021 study5 in Microbiome, disagree.5 By comparing the oral microbiota of biological versus adoptive mother-child pairs, they found that contact, age, and a shared environment, rather than genetics, were the main determining factors. To back this up: cohabiting couples had more similar microbiomes than mother-child pairs. Plus, both adopted and biological children more closely resembled their mothers than unrelated women.
What changes them throughout life
All individuals have a core microbiome, or microorganisms present in almost everyone, according to a 2017 NIH article.6 In fact, as a 2013 article points out, The NIH Human Microbiome Project found that the oral microbiome has the largest core set of microbes shared among unrelated individuals (versus other colonized body sites, like the gut and skin).7
In addition to a core microbiome, individuals have a variable microbiome, or bacteria that are unique to them, forming thanks to a combination of genetics and lifestyle choices. In fact, one 2021 study 8 showed that up to 10% of the oral microbiome is dependent on genetic factors and that people with a hereditary risk of dental disease and gingivitis were more likely stimulated by genetics than oral microbiome factors. Then, throughout the lifespan, the oral microbiome changes. Along with diversifying when the teeth erupt, the flora evolve in response to environmental factors.
Researchers know that diet, medications and substances, oral hygiene, health and disease states, stress levels, gene mutations, and contact with others can all have an impact. For instance, according to a 2014 NIH article,9 “the presence of excess carbohydrates is often responsible for altering the local environment to be more favorable for species associated with the initiation and progression of disease.”9 Further, a 2019 review makes the point that tobacco and alcohol, “which are causative factors of oral cancer, may alter the oral microbiome composition.”10
Interestingly, according to a 2020 study, the diversity of the oral microbiota declines with age.11 One possible reason is tooth loss, which would lead to the disappearance of strains that colonize the tooth surface. Researchers continue to investigate whether oral microbiome diversity plays a role in oral health.
1 Deo, P.N., Deshmukh, R. (2019). [Fundamental information about the oral microbiome]. National Library of Medicine.
2 Mason, M.R. et al. (2018). [Study on oral micrbioa communities]. National Library of Medicine.
3 Li, H. et al. (2018). [Study on infant’s oral microflora]. National Library of Medicine.
4 Liu, X. et al. (2021). [Study on human genetic impact on oral microbiome]. Cell Discovery.
5 Murkherjee, C. et al. (2021). [Study on oral microbiome influcence by environment vs. genetics]. Microbiome Journal, Biomedical Central.
6 Demmitt, B. et al. (2017). [Sudy on oral microbiome and genetic influences]. National Library of Medicine.
7 Li, K. et al. (2013). [Analysis of taxonomic memberships of human microbiome]. National Library of Medicine.
8 Liu, X. et al. (2021). [Study on human genetic impact on oral microbiome]. Cell Discovery, National Library of Medicine.
9 Moye, Z.D. et al. (2014). [Study on caries process, carbohydrate metabolism and gene regulation]. Journal of Oral Microbiology, National Library of Medicine.
10 Chattopadhyay, I. et al. (2019). [Study of oral microbiome and oral cancer diagnoses]. Technology Cancer Research & Treatment, National Library of Medicine.
11 Burcham, Z.M. et al. (2020). [Oral microbiota diversity in children and adults]. Scientific Reports, National Library of Medicine.
Sedghi, L. et al. (2021). [Oral microbiome and organisims in oral health]. Wiley Periodontology 2000, National Library of Medicine.
Lamot, R.J., et al. (2018). [Dynamics of communities of oral microbiota]. HHS Author Manuscripts, National Library of Medicine.