2023-12-12 11:00:19
WHAT IS THE MICROBIOTA?
The term microbiota refers to a community of microorganisms that inhabit a specific environment and are distributed in many parts of our body. Its ratio with human cells is 1:1 and its relationship with us is mutualistic, meaning both parties benefit. However, this interaction can be broken, allowing these microorganisms to cause multiple pathologies due to various factors, mainly as a result of alterations in the immune system.
This set of microorganisms are distributed throughout our skin and mucous membranes. Each of these microenvironments has a different composition of communities, in which various microbial genera predominate according to the physicochemical conditions attributed to them.
COMPOSITION OF THE ORAL MICROBIOTA
The oral cavity houses a wide diversity of microorganisms that coexist harmoniously with each other and the host cells. In terms of microbiota, the mouth is the second largest in the human body, after the intestine. It encompasses diverse micro ecosystems that include bacteria, protozoa, viruses and yeasts(1). The human oral microbiome database, known as Human oral microbiome Database eHOMD, reports that there are a total of 774 species of oral bacteria. Of these species, 54% are identified species, 14% are unnamed but cultivable, and 32% are non-cultivable phylotypes.
Most of these microorganisms are present in saliva, while others adhere in different microenvironments of the oral cavity, such as the teeth, palate, tongue, cheeks, oral mucosa and dental prostheses. The six major phyla representing 96% of oral microbiome taxa are Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Spirochaetes, and Fusobacteria. The remaining 4% of taxa consist of the phyla Euryarchaeota, Chlamydia, Chloroflexi, SR1, Synergistetes, Tenericutes and Saccharibacteria. Among the dominant bacterial genera are Streptococcus, Prevotella y Veillonella making up 70% of the oral microbiota.
When bacteria adhere to a surface, they have the ability to form bonds with other microorganisms, forming a network known as a “biofilm.” When not effectively removed through oral hygiene practices, they remain and trap secondary and tertiary colonizers including some pathogenic bacteria. Finally, this leads to the formation of a strong and hardened plaque that is difficult to remove, which gives them protection and can cause bad breath, cavities, dental plaque and oral diseases.
DISEASES ASSOCIATED WITH THE ORAL MICROBIOTA
The interaction between the oral microbiota and the immune system is crucial to maintaining oral health. Normally, these bacteria coexist in harmony, but certain factors can upset this balance and cause dysbiosis, which subsequently affects the activation of immune cells. As a result, oral pathologies such as cavities, periodontitis and gingivitis are triggered.
Furthermore, oral diseases can trigger inflammatory processes that stimulate the release of proinflammatory cytokines. These inflammatory cascades can trigger systemic diseases such as rheumatoid arthritis, endocarditis, bacteremia, cardiovascular, pulmonary, liver diseases and different types of cancer (gastrointestinal, pancreas and breast).
Some defense mechanisms of the immune system contribute to controlling the spread of these microorganisms in the oral microbiota. For example, bacteria, when ingested during digestion, must overcome multiple barriers such as stomach acidity, peristalsis, the alkalinity of bile and pancreatic juice, as well as all the chemical barriers of the mucous membranes. These factors regulate the bacterial concentrations that pass through, making it difficult for them to pass to the rest of the digestive system. However, it has been reported that part of the intestinal microbiota shares characteristics with the oral microbiota due to the passage of some microorganisms that evade the body’s barriers, therefore, it has also been reported that imbalances in the oral microbiota can also cause alterations in the intestinal microbiota and cause other related pathologies.
FUNCTIONS OF THE ORAL MICROBIOTA
The oral microbiota plays various roles in maintaining oral health. One of them is to prevent the colonization of external pathogens. This is achieved by the adhesion of microbiota microorganisms to the surface of the tooth or tongue, creating a barrier that inhibits the invasion of pathogenic bacteria. The adhesion process is based on specific structures present in the envelope of the microorganisms, which bind to molecules of the dental tissue or oral mucosa. By occupying this space, the microbiota can take advantage of favorable environmental conditions, such as the availability of nutrients and the physicochemical factors that promote its growth and proliferation.
In addition, certain microorganisms in the microbiota have the ability to produce antimicrobial substances. When they consume the nutrients available in the mouth, they secrete acidic or harmful substances that can affect the structures of other bacteria, among them we have bacteriocins, which have bactericidal properties.
On the other hand, the oral microbiota plays a crucial role in the metabolism of carbohydrates and dietary compounds. It has the ability to metabolize these substances, facilitating their absorption by the host. This metabolic function is important to ensure proper nutrient utilization and overall health.
Finally, the microbiota has an impact on the immune system. Microorganisms are made up of molecules that the immune system recognizes as antigens. As a result, they stimulate our immune system, which leads to training immune cells to differentiate between self and foreign agents. This immune modulation is essential so that the body can respond effectively to external agents that may pose a threat to oral health.
HOW DO YOU STUDY THE ORAL MICROBIOTA?
Many of the microorganisms that make up the oral microbiota are difficult to isolate in laboratory cultures for their characterization, because they are demanding in terms of their nutritional requirements or physicochemical factors, sometimes it is difficult to simulate their optimal conditions and they easily lose their viability due to lack of requirements, therefore thanks to the development of molecular biology, it has been urged to extract the genetic material of the entire microbial community, allowing the diversity and richness of the microorganisms that make it up to be characterized.
Among the techniques used are nucleic acid sequencing, recombinant DNA technology, the study of the genome, metagenomics (Studies both the bacterial genome and the host genome). This allows the classification of bacteria phylogenetically, leading to the study of what is known as the microbiome, which is defined as the complete genomic content of the community of commensal, symbiotic and pathogenic microorganisms that inhabit a particular place in the human body.
If you want to know more, you can access the Human Microbiome Project (HMP) developed by NIH since 2007, after having completed the human genome project. Its goal is to completely sequence the genome of microorganisms that grow inside the human body. This has allowed the creation of databases that preserve the information of all those microorganisms discovered and allow the characterization of all human microbiomes.
CONCLUSION
The oral microbiota is a community of microorganisms that inhabit our oral cavity, playing a fundamental role in the general health of the host. Their relationship is mutualistic and their key functions such as preventing the colonization of pathogens, producing antimicrobial substances, facilitating nutrient absorption and modulating the immune system, highlight their importance. However, the imbalance of interactions between the oral microbiota and the host generates dysbiosis and triggers multiple oral and systemic pathologies. The continuous study of the oral microbiota, supported by advances in molecular biology and sequencing techniques, provides essential knowledge to understand its diversity, function and its impact on human health, opening new perspectives in the prevention and treatment of various diseases.
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This article is sent to us Laura Ospina Mateusbacteriologist, Master in Microbiology and professor at the Universidad del Sinú Sectional Cartagena (Colombia)
Scientific references and more information:
de Heredia, C. B. (2017). Microbiota autóctona. Farmacia profesional, 31(2), 17-21.
Morrison, A. G., Sarkar, S., Umar, S., Lee, S. T., & Thomas, S. M. (2023). The Contribution of the Human Oral Microbiome to Oral Disease: A Review. Microorganisms, 11(2), 318.
Tan, X., Wang, Y., & Gong, T. (2023). The interplay between oral microbiota, gut microbiota and systematic diseases. Journal of Oral Microbiology, 15(1), 2213112.
Morrison, A. G., Sarkar, S., Umar, S., Lee, S. T., & Thomas, S. M. (2023). The Contribution of the Human Oral Microbiome to Oral Disease: A Review. Microorganisms, 11(2), 318.
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