Bacteria that live in the mouth: characteristics, types and functions

What types of bacteria inhabit the mouth, and what functions do they perform in our body? Let's take a look.

Bacteria are everywhere, even if we are not able to see them at first sight. Various studies estimate that, of the 550 billion tons of organic matter present in the environment in the form of carbon, 70 billion tons correspond to bacteria living in ecosystems. In other words, the bacterial mass of soils and waters contains 15% of all the organic matter on the planet, a value second only to that of plants (450 gigatons, 80%).

However, it is not necessary to go to an astronomical scale to realize that bacteria are everywhere. If you are reading this from your cell phone, you may be surprised to learn that there are more than 25,000 bacterial units per 6.5 square centimeters of screen space (more than a toilet). Yet another shocking fact: between your elbow and your fingertips there are up to 10 million bacteria, all living on our epidermal surface.

With all these figures, it is more than clear that there are bacteria everywhere. The human being is an open system and, as such, is not free from the colonization of microorganisms in different parts of the tracts that exchange substances with the environment, such as the nostrils, stomach, esophagus, eyes, anus or mouth. In order to explore a terrain of great interest, today we explore in a brief way the bacteria that live in the mouth.

General concepts about the microbiome

Before looking at the microorganisms living in the mouth, it is necessary to establish a number of basics regarding our relationship with bacteria. The term "flora" is often used to designate the colonies present in our tracts and mucous membranes, but these Biological units have nothing to do with the Plantae kingdom. Therefore, the more appropriate terms are "microbiome", "microbiome" and "microbiome", the more appropriate terms are "microbiome" or "normal microbiota"..

The human microbiota is divided into two categories:

• Autochthonous microbiota: this is that which encompasses microorganisms that inhabit within the human system for an extended period of time. Due to its close relationship with the host, it has evolved together with it by symbiosis mechanisms.
• Allochthonous microbiota: these are microorganisms that do not require the host to live, so they can be found in any ecosystem. However, they can end up on the surface or tracts of the human being in a transitory way.

The autochthonous microbiota can be commensal or symbiotic, but never harmful in a normal situation.. The last thing a bacterial community living in equilibrium with humans wants is to cause pathogenesis, because if humans die, the population of microorganisms also disappears. Unfortunately, some symbiont or commensal bacteria can become a problem, especially in patients with immunosuppression (AIDS) or concomitant diseases (such as cancer).

In addition, the microbiota can be latent (remains relatively constant throughout life) or transient (shows continuous fluctuations according to the (it presents continuous fluctuations according to the age of the host, the environment or the season). In general, the microorganisms essential for human life are those that are autochthonous and latent.

What bacteria live in the mouth?

The terms "oral microbiome", "oral microbiota" or "oral flora" refer to the same thing: the microorganisms that inhabit the human oral cavity. However, rather than the number of bacteria per square centimeter of tissue, what is usually estimated is the bacterial genome present in the samples. In other words, the wealth of living beings that inhabit our mouths is determined by the detection of genes of different species and strains, not by direct observation of the bacteria in our mouths.not by direct observation of them. This is because, for example, some of the microorganisms described cannot be cultured in the laboratory.

The oral cavity contains one of the most intricate and complex microbiomes in the entire human body, perhaps second only to the intestines and the digestive processes that take place there.

To give you an idea, it is estimated that one milliliter of saliva contains 10 to 8 microbial units.which are distributed among about 700 taxa of prokaryotic organisms. At a general level, a healthy "oral flora" is thought to be composed of about 200 bacterial species.

The oral biome is extremely diverse for the simple reason that there are many small-scale niches to exploit. We have the saliva, the surface of the teeth, the gums, the tissues and mucosa of the inner cheek, the palate, the sub and supragingival plaques and the tonsils, among many other structures. Each of these surfaces favors a different composition of the microbiome.

According to the Human Oral Microbiome Database (HOMD), only 57% of the bacterial species inhabiting our mouths have been officially described and catalogued, 13% have been cultured, and 13% have been cultured.13% have been cultured but not classified and 30% have not even been cultured in the laboratory environment. Yes, as strange as it may seem in this day and age, we don't even know for sure which microorganisms help us to survive.

The main bacterial groups in the mouth

As indicated in the study "Oral microbiome: Unveiling the fundamentals", the oral bacterial communities have been grouped into 185 genera and 12 phyla, oral bacterial communities have been grouped into 185 genera and 12 different phyla.. These phyla are as follows: Firmicutes, Fusobacteria, Proteobacteria, Actinobacteria, Bacteroidetes, Chlamydiae, Chloroflexi, Spirochaetes, SR1, Synergistetes, Saccharibacteria (TM7) and Gracilibacteria (GN02).

In any case, it should be noted that the fluctuation of many of these microorganisms is changeable, i.e., some are allochthonous, transient, or both. Food consumption, drug use (such as smoking, since smoke enters through the mouth), oral hygiene and changes in the pH of the oral environment may cause increases or decreases in colony numbers of a given species.. Therefore, this medium is quite volatile and difficult to study.

The functions of the oral microbiome

The oral microbiome usually presents itself in the form of a biofilm, that is, as an organized "microbial mat" attached to a surface or substrate, in this case the teeth, mucous membranes and oral tissues. Once this biological community is established, the components secrete a protective extracellular matrix, which further binds the microorganisms together.that further binds its members together. This is what is known as "dental plaque" and, although it has to be kept under control by constant brushing, it is not in itself bad for the body.

The formation of oral biofilm is essential to maintain the homeostasis of this environment and to prevent the pathogenesis of other microorganisms.. The premise is simple: if a bacterial colony is already established on a given surface, it is much more difficult for another potentially pathogenic colony to start proliferating in the same place. This is a clear example of symbiosis (albeit involuntary), since the space is already occupied, the host is indirectly protected from unnecessary invasion.

Furthermore, in the oral community there are bacteria that express the enzyme nitrate reductase, thus converting nitrate to nitrite when nitrate-containing compounds enter the mouth. This means that, together with the enzymatic action of saliva, digestion starts from the oral cavity thanks to the help of bacteria.

Beyond all this, it has also been demonstrated that these microorganisms are essential for the specialization of the immune system in early stages of development.The bacterial populations are able to keep pro-inflammatory responses at bay and even to actively fight other pathogens. Some bacterial populations are able to secrete bactericidal substances into the environment, which directly protect us from the invasion of harmful germs.

Summary

Surprising as it may seem in the boom of scientific innovation and knowledge, there are still an infinite number of things we have yet to know. The lines written are a clear example of this, because although we know that the oral microbiota is essential for our systemic wellbeing, we have not yet been able to classify almost half of the microorganisms that live there.

In any case, what is clear to us is that, as a species, we are nothing without our microbes. The bacteria that inhabit our systems are essential for fighting disease, training the immune system, digesting food and much more. Without them, life as we know it today would not be possible.