What role does the oral microbiota play in your health?

In recent years, interest in the study of the oral microbiota as a marker of health status has increased enormously. More and more research is being carried out in the field of microbiology and, therefore, the conclusions we can draw are more scientifically validated. 

 

Difference between microbiome and microbiota.

Before going into depth, let us clarify a frequently asked question: is the microbiome the same as the microbiota, and how do they differ? Although we can sometimes see these terms interchanged as synonyms, there are differences in their meaning. The microbiome is the set of all the microorganisms that naturally inhabit our body and its DNA, i.e. it refers to the collection of genomes of all the microorganisms in the environment or specific space: the human body, an ocean, a substrate, a plant… 

On the other hand, microbiota refers to the set of microorganisms (bacteria, viruses and fungi) found in a specific environment or space, which is usually a part of the human body (oral, intestinal, skin microbiota…), but there is microbiota in an ocean, a substrate or a plant, as we said before, but without specifically studying the genome of these microorganisms. The microbiota can be described through various methods, for example, by observation through a microscope, or by analyzing the DNA of those microorganisms present in that particular space, which is the methodology we use at 24Genetics.

 

Functions of the oral microbiota

The microbiota plays a fundamental role in human health, in fact, in our body the number of prokaryotic cells (bacteria and archaea) is greater than the number of human cells, accounting for about 3 kilos (around 6.5 pounds) of our body. The oral  microbiota protects us against pathogens, helps the development of our immune system, and facilitates the digestion of food to produce energy. 

 

The impact of bacteria on our bodies

In the early 1990s, it was thought in academia that the sequencing of the human genome would be sufficient to understand the basis of health and disease. However, the analysis of the human genome was only an introduction to the genetic composition of our organism. Humans and their commensal microorganisms have evolved together over the last two million years, becoming dependent on each other (Avila et al., 2009). 

The study of the microbiota dates back to the early 20th century, and its inception is attributed to Elie Metchnikoff, one of Pasteur’s students. Metchnikoff highlighted the beneficial effects of lactic ferments on the intestinal microbiota (then called flora), and on our organism in general. As a result of this work, he launched the idea that bacteria belonging to the intestinal flora, far from being pathogenic, play an essential role in our health. 

Over time, microbiological studies focused on these bacteria revealed their role in various aspects of our organism, especially in the absorption of vitamins and nutrients, as well as in strengthening our immunity.

Since 2006, scientific and technological advances in high-throughput sequencing have enabled scientists to decipher the bacterial genome of our microbiota, both intestinal and from other areas of the body. Thanks to this process, the properties of numerous previously unknown bacterial species have been discovered and analyzed, since most of them cannot be cultured in vitro.

These advances have led to two important discoveries. Firstly, it has been shown that each individual possesses his or her own unique microbiota, although there is a constant distribution of bacterial species found in all healthy individuals, forming a common basis. Secondly, it has been observed that there are differences between the microbiota of healthy and diseased individuals, both in the diversity of the microbiota and in the organisms found in it and their proportions (Alvarez et al., 2021). 

 

Difference between Eubiosis and Dysbiosis

In the study of the microbiota, it is important to consider the concepts eubiosis and dysbiosis. The term eubiosis is used to describe the normal and balanced state of the microbiota, so that it meets the necessary requirements for us to benefit from its positive effects on our health. On the other hand, the term dysbiosis is used to refer to an imbalance in the bacterial composition of an ecological niche compared to the pattern considered normal and balanced. In dysbiosis, there may be a temporary or permanent disappearance of some of the beneficial health effects.

 

What is the Oral Microbiota

The oral cavity contains the second largest and most diverse microbiota in the body, second only to the intestine, and is home to more than 700 species of bacteria, including commensal, symbiotic and pathogenic species. 

The oral microbiota is found in the saliva on the surface of the gums and teeth, forming biofilms. Biofilms are complex, structured bacterial communities that adhere to a surface and are enveloped in an extracellular matrix produced by the bacteria themselves. These bacterial communities form a kind of “home” where they can interact and protect each other, creating a structure resistant to external attacks (Lasa et al., 2005).

A large number of studies have shown that the mouth’s microbiota in healthy individuals remains stable and is not usually pathogenic. However, under certain circumstances, certain bacteria can become destructive and lead to the development of oral diseases such as periodontitis, and even affect health at the systemic level. 

The oral microbiota can be classified into: 

• Core  microbiota (common to all): refers to bacterial species that are consistently present in all individuals.
• Variable microbiota (different among individuals): refers to bacterial species that vary among individuals in response to their lifestyle, phenotype and genotype.

 

What factors alter the oral microbiota?

The oral microbiota can be altered by endogenous factors, such as genetics, age, and ancestry, and exogenous factors, such as smoking, diet, alcohol consumption, antibiotics, or pregnancy. This can disturb the bacterial balance, leading to infectious diseases in the oral cavity, such as caries or periodontitis (Figure 1). 

Figure 1. Human diversity determines the composition of the oral microbiome. Genetics, ethnicity, socioeconomic status (through its influence on diet and alcohol consumption), smoking and age affect the composition of an individual’s oral microbiome. Source: (Herremans et al., 2022).

 

Therefore, the factors affecting the microbiota that we can control are diet, smoking and alcohol consumption. 

In terms of diet, a high consumption of sugars facilitates the growth of acidogenic bacteria, i.e., those that produce lactic acid as a result of sugar fermentation. These bacteria include both those that lead directly to caries and those that create the necessary environment for secondary invasive bacteria to cause caries. On the other hand, a diet rich in fiber and dairy products helps to maintain a balanced microbiota (Santonocito et al., 2022). 

Alcohol consumption increases gram-positive bacteria, such as Streptococcus mutans and species of the genus Lactobacillus, which can cause dental caries. In addition, oral bacteria convert ethanol to acetaldehyde, which is a carcinogen (Li et al., 2022).

However, moderate consumption of red wine can improve oral health, as it contains a mixture of organic acids, which are active against oral streptococci responsible for caries (Esteban-Fernandez et al., 2018).

Tobacco in turn has a great influence on the oral microbiota  as it increases the acidity of saliva, reduces oxygen in the oral cavity, influences the adhesive capacity of oral bacteria and weakens the host immune system. In addition, cigars carry a large number of different bacteria, some of which, such as species of the genus Bacillus and species of Clostridium, can survive the smoking process and colonize the oral cavity (Wu et al., 2016). 

 

Oral microbiota and oral health.

A healthy oral microbiota helps prevent the overgrowth of harmful bacteria, as beneficial bacteria compete with pathogenic bacteria for available resources and space. These beneficial bacteria can also produce antimicrobial substances that help maintain a healthy oral environment. Among the genera of bacteria that are considered beneficial, because they have anti-inflammatory properties, are Haemophilus and Neisseria. 

On the other hand, imbalances in the oral microbiota can lead to oral diseases such as caries and periodontal disease. Caries are caused by the production of acids by bacteria that break down food debris and form dental plaque, which damages tooth enamel. Periodontal disease, on the other hand, is characterized by inflammation of the gums and damage to the supporting tissue of the teeth, due to the presence of pathogenic bacteria in dental plaque such as “Porphyromonas gingivalis”.

In addition, the influence of oral microbiota on oral cancer through different mechanisms has been demonstrated in recent years (Figure 2): 

• Oral infections and dysbiosis are responsible for promoting a proinflammatory microenvironment, in which inflammatory cytokines and matrix metalloproteinases favor tumor development and progression. 
• Bacteria in the oral cavity produce reactive oxygen and nitrogen species as well as oncogenic metabolites (e.g., nitrosamines) to induce genetic damage in oral mucosal cells. 
• Oral dysbiosis leads to altered epithelial barriers, which predispose the oral mucosa to the development of chronic precancerous lesions. 
• Finally, oral dysbiosis is responsible for several epigenetic alterations, which promote tumor development (e.g., alteration of onco-miRNAs or DNA methylation phenomena).

 

Figure 2. Mechanisms through which oral dysbiosis can lead to oral cancer. Source: (Radaic & Kapila, 2021)

 

Oral microbiota and systemic diseases

On the other hand, oral microbiota may promote the development of systemic diseases such as pancreatic cancer or lung cancer. Although the causality of the microbiota in the development of these diseases has not been demonstrated, an association has been proven and, for example, in lung cancer there is growing evidence that the oral microbiome could influence the development and progression of this disease. It has been observed that certain microorganisms present in the oral microbiota can migrate into the lungs through aspiration or inhalation, which could trigger a chronic inflammatory response in the lungs. This chronic inflammation, in turn, may contribute to the development of pre-existing conditions that increase the risk of lung cancer, such as chronic obstructive pulmonary disease (COPD) or chronic bronchitis (Maddi et al., 2019).

Finally, there is growing evidence of a link between periodontal disease, with a clear influence of the oral microbiome, and systemic diseases such as Alzheimer’s disease, among others. Periodontitis is a chronic inflammatory disease that affects the tissues surrounding and supporting the teeth. It is characterized by the accumulation of bacterial plaque and inflammation of the gums, which can lead to bone loss and the formation of periodontal pockets. People with periodontitis have been observed to have higher levels of inflammatory markers in the body suggesting that the chronic inflammation associated with periodontitis may play a role in the development and progression of Alzheimer’s disease. In addition, specific periodontal bacteria have been identified in the brains of patients with this disease. It has been theorized that these bacteria could travel from the oral cavity to the brain, triggering an inflammatory response and contributing to the neuronal damage characteristic of Alzheimer’s disease (Asher et al., 2022; Dominy et al., 2019).

 

Oral microbiota and 24Genetics

At 24Genetics we have launched an oral microbiota test, based on the analysis of the genome of microorganisms present in saliva, including bacteria, viruses and fungi. In addition to knowing the composition of your oral microbiota, you will be able to discover your direct predisposition to periodontitis and indirect predisposition to other pathologies. Click here to learn more about our new test.

 

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