These microorganisms populate our body, helping in processes such as digestion, immunization and others.
Therefore, the limitation of antibiotics and the use of prebiotic and probiotic foods are on the rise. The benefits of maintaining a balanced microbiome, not only in the gastrointestinal tract but in the rest of the body, are becoming more widely known. Here we will discuss everything you need to know about the types of microbiota in the human body and how to keep them as healthy as possible.
- We recommend you read: “Microbiota: what is it and what is it for?”
Types of microbiota in the human body: an ancestral symbiosis
Bacteria are unicellular microorganisms that can be free-living, symbiotic, or parasitic. The various strains that inhabit the human body are, for the most part, of a commensal or symbiotic nature, since they obtain benefits from inhabiting a living environment and the host also receives some type of gain.
Some of the positive aspects of the microbiota on the host are summarized in the following lines:
- It helps in the digestion of certain foods.
- They produce vitamins that are not obtained naturally.
- They promote the specialization of the immune system.
- It prevents other pathogenic microorganisms from colonizing the internal environment of the individual.
- They promote the development of certain physiological systems.
As we can see, we are facing an ancestral symbiotic relationship . The life of the human being, as we know it, would not be possible without these small living beings and vice versa. Even so, it is necessary to make distinctions between the colonies of bacteria that live with us.
The autochthonous microbiota is one that accompanies the host for long periods of time (even a lifetime). They have evolved together with the species they inhabit, and usually participate in physiological processes intrinsic to the system in which they live.
The non-native microbiota, on the other hand, is in our passing body. For example, when we touch certain surfaces or receive certain foods, our epithelial or intestinal microbiome may change, but those bacteria are just transient travelers. Due to their volatile nature and ability to colonize other environments by themselves, these microorganisms do not perform physiological functions in our body.
Also, depending on a merely temporary variation, the microbiota can be latent or transient, terms broadly linked to those discussed above.
Once we have specified what the microbiome is from a general point of view, we will talk about the types of microbiota in depth .
1. Gut microbiome
The composition and activity of the gut microbiota depends on host genetic factors, nutrition, and lifestyle. Despite general knowledge, limited to the benefits it brings to the gastrointestinal tract, various studies underline that this microbial system plays essential roles in metabolic pathways, specializations of the immune system, and signaling processes that connect the stomach, muscles, and brain .
Some of the benefits that the intestinal microbiome confers on the human species are the following:
- Digestion of carbohydrates such as cellulose and hemicellulose of plant origin, which expands the human diet.
- It promotes the specialization of the immune system as it is one of the first microorganisms to colonize the individual.
- It protects the colonization of other pathogenic bacteria, as they compete with them for resources, space and some produce antimicrobial substances.
- They promote the correct development and functioning of the gastrointestinal tract in neonates.
- They allow optimizing the calories obtained by various foods, which in impoverished environments translates into greater weight with less quantity.
The intestinal microbiota fulfills a series of essential functions for the survival of the organism in which they live. The predominant bacterial phyla in the gastrointestinal tract are the following:
- Firmicutes , with an abundance of 65%.
- Bacteroidetes , with a relative abundance of 23%.
- Actinobacteria , with a relative abundance of 5%.
2. Microbioma vaginal
Although the intestinal microbiota is the reigning example of bacterial symbioses, there are other systems that greatly benefit from the presence of these microorganisms. The vaginal microbiota is a clear example of this .
The main colonizers of this environment are Lactobacillus, a genus of elongated Gram-positive bacteria of a microaerophilic nature (that is, they require oxygen in small quantities to survive). It is important to know that the presence of estrogen and progesterone, hormones that mark the reproductive life stage of women, promote the proliferation of these microorganisms.
Lactobacilli produce lactic acid, a substance that promotes an acidic pH vaginal environment that limits the growth of potential pathogens. In addition, some strains produce hydrogen peroxide and bacteriocins, antagonistic products that inhibit the proliferation of harmful bacteria.
There are many other types of colonizing microorganisms beyond Lactobacillus, such as the genera Actinomyces, Aerococcus, Allisonella, Alloscardovia, Anaerococcus, Arcanobacterium and Atopobium, among others. About 100 to 200 species are counted in this microenvironment, and their fluctuation is defined by the oral and rectal microbiota, as well as genetic and environmental factors.
3. Microbioma oral
The human mouth contains multiple microenvironments, including the teeth , tongue, cheeks, and palate among others. It is estimated that due to its extensive contact with elements external to the human body itself (food), the oral microbiome has a great wealth of microorganisms, around 600 to 1000 different species. Some of the genera are Actinobacteria, Bacteroidetes, Chlamydiae, Chloroflexi, Euryarchaeota, Firmicutes, Fusobacteria, Proteobacteria, and Spirochaetes.
Some of the benefits that the oral microbiota produces at the organic level in humans are the following:
- It helps transform the nitrate present in some foods into nitrite, a substance with antimicrobial capacity.
- Like the vaginal microbiota, it secretes bacteriocins, which inhibit the growth of pathogenic microorganisms.
- Contributes to the correct maintenance of mucosal surfaces.
- Contributes to food metabolism.
But not everything is positive, since some microorganisms that live inside the human mouth generate the well-known bacterial plaque , an association of bacteria and sugars that continuously adheres to our teeth. This is the main cause of cavities, gum pathologies such as periodontitis and tartar formation.
Conclusions
The microbiota, as we have seen, is almost a “ghost organ” within the human body . Especially the intestinal one, which is capable of performing complex functions that no human physiological framework could conceive.
It is necessary to limit that the vagina, the intestine and the mouth are not the only places that present bacteria. As cited by various studies, any surface in contact with the environment is susceptible to the appearance of bacterial colonies. This includes the skin, eyes, rectum, upper respiratory tract, and the environments listed above.
Such is the importance of bacteria in the human body that there is a relatively new branch of science charged with studying them. Metagenomics, defined as obtaining genetic material from environmental samples, can also be applied to the human body. Thus, researchers are able to sequence the DNA and genetic information of the symbiotic microorganisms that live with us. This is known as the “extended DNA” of the human being.
We live in a society full of stimuli and atypical consumer products for our species, such as alcohol, tobacco and other drugs. This, together with stressful lifestyle habits, can unbalance the microbiota (especially the intestinal microbiota), which translates into various pathologies of varying severity. For this reason, the use of prebiotics and probiotics, substances that promote the balance of the bacterial flora, are increasingly in use. One thing is clear: a correct microbiota promotes an adequate state of health in the individual.
Bibliographic references
- Lloyd-Price, J., Abu-Ali, G., & Huttenhower, C. (2016). The healthy human microbiome. Genome medicine, 8(1), 1-11.
- Ursell, L. K., Metcalf, J. L., Parfrey, L. W., & Knight, R. (2012). Defining the human microbiome. Nutrition reviews, 70(suppl_1), S38-S44.
- Mendling, W. (2016). Vaginal microbiota. In Microbiota of the human body (pp. 83-93). Springer, Cham.
- Nicholson, J. K., Holmes, E., Kinross, J., Burcelin, R., Gibson, G., Jia, W., & Pettersson, S. (2012). Host-gut microbiota metabolic interactions. Science, 336(6086), 1262-1267.
- Sekirov, I., Russell, S. L., Antunes, L. C. M., & Finlay, B. B. (2010). Gut microbiota in health and disease. Physiological reviews, 90(3), 859-904.
- Dewhirst, F. E., Chen, T., Izard, J., Paster, B. J., Tanner, A. C., Yu, W. H., … & Wade, W. G. (2010). The human oral microbiome. Journal of bacteriology, 192(19), 5002-5017.
- Wade, W. G. (2013). The oral microbiome in health and disease. Pharmacological research, 69(1), 137-143.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.