Exploring the oral microbiota

Here at Yakult we are very interested in the role of the gut microbiota and its importance for human health. However, with it being National Smile Month (18th May – 18th June 2020) this got us thinking about the bacteria in our mouths - the oral microbiota. So, we are moving back up the gastrointestinal tract, to where it all begins - the mouth, to share with you some facts about this cavity.


What is the oral microbiota? 

Within the mouth, there are eleven distinct regions including the teeth, cheeks and tongue.1 Together, the microbes that live on all regions within the mouth constitute the oral microbiota. There are over 600 bacterial species in the human mouth, but the specific species and number of bacteria varies between the regions of the mouth and between individuals.2-3

Oral Microbiota

Development of the oral microbiota

Similar to the gut microbiota, early colonisers of the infant oral microbiota are influenced by mode of birth and feeding, as well as the maternal oral microbiota.As a child ages their oral microbiota becomes more diverse. At 6-months of age Firmicutes is the most abundant phyla, but its relative proportion, along with the Actinobacteria phyla, decreases as the child ages, whereas the relative proportions of Proteobacteria, Bacteroidetes and Fusobacteria increase.5

Tooth eruption is an important stage for the oral microbiota as these non-shedding surfaces allow higher species diversity to develop. Interestingly, as people age and they lose teeth the oral microbiota starts to resemble that of a child again, before tooth eruption.6


The oral microbiota and health

The relationship between humans and the oral microbiota is symbiotic. It plays an important role in maintaining oral homeostasis to protect the oral cavity and prevent the development of disease. Alterations to the oral microbiota have been associated with several oral diseases such as dental caries, periodontitis and oral cancers.7 Furthermore, the oral microbiota has been associated with diseases or conditions outside of the oral cavity, such as diabetes, obesity, inflammatory bowel disease and rheumatoid arthritis.7-8 So far, much of the research has only shown that the oral microbiota of those with such diseases differs from healthy controls, but the mechanism underlying this is yet to be understood.7 


Factors that influence the oral microbiota 

The oral microbiota is described as being ‘dynamic’ because it changes in response to host, environmental and lifestyle factors. Diet, alcohol consumption, smoking, antibiotic use, pregnancy and dental hygiene practices have all been associated with the oral microbiota.1,6 

For example, a study comparing the oral microbiota of non-smokers, former-smokers and current smokers showed that current-smokers had depleted levels of Proteobacteria. Interestingly, the oral microbiota of former-smokers was more alike to those who had never smoked than those who currently smoke, which suggests that the oral microbiota may be able to restore itself once you stop smoking.9

Interestingly, probiotics that are generally considered to have their actions in the gastrointestinal tract have also been shown to transiently colonise the oral cavity10, and therefore researchers are exploring whether probiotics may have a role to play for oral health.  


The ease of access to the oral cavity allows this dynamic microbial community to be explored. We are beginning to understand how these microorganisms can be important for both oral and systemic health, and through learning how they can be altered by environmental factors we will begin to understand how we can use this to our advantage.  



1. Jia et al. (2018) British Dental Journal 224(6): 447-455.

2. Chen et al. (2010) Database 2010: baq013.

3. Hall et al. (2017) npj Biofilms and Microbiomes 3:2.

4. Kilian (2018) European Journal of Oral Sciences 126(1): 5-12.

5. Kennedy et al. (2019) Scientific Reports 9: 19025.

6. Deo and Deshmukh (2019) Journal of Oral and Maxillofacial Pathology 23(1): 122-128.

7. Lu et al. (2019) Food Science and Human Wellness 8(1): 8-15.

8. Gao et al. (2018) Protein & Cell 9(5) : 488-500.

9. Wu et al. (2016) The ISME Journal 10: 2435-2446.

10. Sutula et al. (2013) Microbial Ecology in Health and Disease 24: 10.3402/mehd.v24i0.21003