6 The Oral Microbiome
The Oral Microbiome
The oral microbiome as with other site-specific microbiomes on and inside the human body is very distinct for each individual and its makeup and function is reflective of a variety of factors. Even within the context of the oral cavity, there are several unique niches with their own microbial ecosystem, including saliva, tongue, teeth, gingiva, throat, tonsils, and others. Each of these habitats exhibit diverse and complex interactions between bacteria, archaea, fungi, viruses, and protozoa, where dysfunction can lead to a number diseases, both rare and common (Wade, 2013, Sampaio-Maia et al., 2016).
Factors Affecting Composition
The composition of the oral microbiome and its respective niches is inherently dependent on host genetics, but other factors and habits such diet and smoking have a substantial effect on diversity. Members of the oral cavity demonstrate more heritability than the gut microbiome, and higher abundances of certain heritable organisms, such as Prevotella pallens, are associated with a lack of dental caries, while on the other hand, Streptococcus mutans and Lactobacillus species are linked to cavities (Davenport, 2017, Xiao et al., 2018). Detection of the specific groups of microbes has traditionally been difficult since many are fastidious and cannot be cultivated. So other techniques like metagenomics, metatranscriptomics, and proteomics have been implemented to better characterize the microorganisms present and their respective roles (Parahitiyawa et al., 2010, Grassl et al., 2016). These studies have found that the oral microbiota is quite different even between healthy individuals, and so it may be the microbial functionality that is more important in the progression of various diseases, such as the role of biofilm formation, plaque buildup, and sugar metabolism in the development of dental caries (Segata et al., 2012, Takahashi et al., 2010, Duran-Pinedo and Frias-Lopez, 2015, Sato et al., 2015, Davenport, 2017).
Dysbiosis and Disease
The oral cavity is such a dynamic location that constantly experiences a variety of different foods, drinks, oral hygiene products, and other environmental stimuli with each composed of a multitude of macromolecules, compounds, and potentially other microorganisms, and so it makes sense that its microbiome often fluctuates in diversity (Parahitiyawa et al., 2010). Though there are differences in composition between individuals, specific sites, and over periods of time, species such as Streptococcus mitis and Granulicatella adiacens are conserved and generally present throughout the oral microbiome, while the presence of other specific microbes are associated with a particular disease (Aas et al., 2005). However, diseases like Periodontitis, which is the chronic inflammation of the gums and tooth supporting structures and one of the most common oral diseases, has many organisms associated with the condition, so discerning which ones are primarily re