Intestinal flora: what is it, its characteristics and functions?

Let's see what are the characteristics of the intestinal flora and its functions in the human body.

Bacteria are unicellular prokaryotic microorganisms (consisting of a cell without a nucleus) with a maximum size of 5 micrometers and an immense diversity of forms and aggregations.

As they are invisible to the human eye without microscopy methods, we tend to overlook the importance of these microorganisms at the biological level, but nothing could be further from the truth.But nothing could be further from the truth: the total biomass of the planet is estimated at 550 gigatons, 15% of which corresponds to bacteria.

To give you an idea, the amount of carbon present in animals is 2 gigatons total, 35 times less than the biomass provided by these microorganisms. It is impossible to understand an ecosystem without bacteria, since their work ranges from participating in the natural cycles of elements such as nitrogen, carbon and phosphorus, to the transformation of organic substances into inorganic ones and vice versa. Simply put, without bacteria there would be no life.

Beyond an ecosystemic or global scale, it is striking to discover that our own body would not sustain itself without bacterial action. Today we come to talk to you about the microbiome present in the human being, more specifically, the intestinal flora.

What is the microbiome?

We usually refer to the set of bacteria that inhabit our body as "intestinal flora". This is a mistake, because these microorganisms have nothing to do with the set of plants in a geographical region. Although we will keep this terminology for informative purposes, it is important for you to know that the proper term is the microbiome.

The microbiome (or normal microbiota) refers to the set of microorganisms that are usually located in different sites in the bodies of multicellular organisms, such as the human body.such as the human body. As unpleasant as it may seem at first glance, the reality is that we have bacteria in any part of our body that is in contact with the outside. This includes the eyes, skin, nostrils, genital organs, intestines and many other areas.

The microbiota, based on their dependence and time of stay in the human being, can be classified into several types. We will tell you about them briefly:

• Autochthonous microbiota: those microorganisms that colonize the human being for a prolonged period of time. They are symbionts, as they have co-evolved with us.
• Allochthonous microbiota: they do not need us, so they are found in other habitats beyond the human body. They occupy our microbiome transiently.
• Latent microbiota: which are present for (almost) the entire life of the host. Their populations do not fluctuate dramatically, unless pathologies occur.
• Transient microbiota: their population fluctuations are continuous, so it follows that these bacteria are not indispensable to the host.

What is the intestinal flora?

Based on the terms previously described, we can define the intestinal flora as the set of microorganisms in a defined environment, in this case, the digestive tract.. Due to its close proximity to the human being and symbiotic work with our organism, it can be said that most of the bacterial colonies that we are going to name are autochthonous and latent, that is to say, indivisible to the gastric functioning of our species.

Every adult human being harbors about 100 trillion bacteria in his or her body, representing about 400 different species.. Although the presence of these microorganisms is not very high in the stomach due to the presence of acids, as we move along the gastrointestinal tract things become more interesting.

For example, the concentration of bacteria is increasing along the small intestine, from 10^4 bacteria/ml in the proximal duodenum to 10^7 bacteria/ml in the terminal ileum. Together, the bacterial population of the colon can total up to 600 grams in weight, representing more than 95% of the total host microbiome. Incredible numbers, isn't it?

The intestinal flora has co-evolved with the human being in a symbiotic type of relationship, where both components receive clear benefits. It is true that humans can "survive" without the gut microbiota, but experimental studies with mammals have shown that its long-term absence stimulates abnormal development. Dysbiosis (or bacterial mismatch in the gut) can cause multiple health problems in the short and long term.

What species are found in the intestinal flora?

The composition of the intestinal flora in humans is very variable.It depends on geographical location, diet, age and many other factors. In any case, several studies have proposed, in consensus, 3 predominant phyla in this type of microbiome:

• Firmicutes (65%): this phylum represents more than 200 bacterial genera in the intestines, the most important being Mycoplasma, Bacillus and Clostridium.
• Bacteroidetes (23%): a large group of anaerobic Gram-negative bacteria.
• Actinobacteria (5%): curiously, they are the most represented phylum in soils. Actinobacteria species account for 64% of the bacterial biomass in the substrates.

On the other hand, at the metabolic level, they are divided into 3 different groupingsLactic acid producers, putrefaction producers and others.

The microbiota belongs to everyone, so it is impossible to generalize beyond this list. At birth, the intestine is sterile, but it is completely colonized during the first year of life. From this point on, fluctuations occur between individuals based on the type of lactation, genetic contribution, diet, environmental factors and an almost infinite list of variables..

The functions of the intestinal microbiome

We have repeatedly told you that the gut microbiome is essential for the well-being of the organism, but why? In the following lines we give you the answers.

1. Metabolism

Although it may not seem so at first glance, the intestines are one of the most active areas of the entire body at the immune level. Therefore, immune responses are partially modulated, immune responses are partially modulated by the intestinal flora, since, among other things, this flora since, among other things, it enables energy saving through carbohydrate fermentation, the synthesis of vitamin B and K and the production of short-chain fatty acids, among many other things.

In addition, symbiont colonies of microorganisms stimulate intestinal development, maintain epithelial turnover, modulate the immune response and participate in the metabolism of certain drugs. Undoubtedly, their functions at the metabolic level are invaluable.

2. Prevention of obesity and diabetes

Although these results should be taken with a pinch of salt, it has been demonstrated in experimental settings that germ-free mice have up to 47% more adipose tissue in experimental settings that mice free of intestinal microbiota (germ-free) have up to 47% more adipose tissue than those with a colonized gastrointestinal tract.. It has also been shown that the microbiome of obese people is very different from that present in people with a standard body mass index, but the causality between the two events has not yet been fully confirmed.

3. Increased food utilization

As mentioned above, some bacteria produce enzymes that are able to degrade molecules capable of degrading molecules that we humans cannot digest on our own, such as cellulose, hemicellulose and pectin, and that we cannot digest on our own..

After certain metabolic reactions, these compounds of vegetable origin are transformed into short-chain fatty acids, digestible by the intestinal mucosa. This, as anecdotal as it may sound, can account for up to 10% of the daily caloric intake of an adult human being.

4. Antibacterial action

Symbiont bacteria in the intestinal tract are occupying an ecological niche from which they do not want to get rid of, so they will defend us against any pathogen that tries to they will defend us against any pathogen that tries to take their place.. The high concentration of microorganisms in these mucous membranes causes a "barrier effect" where, literally, many microorganisms have no place to grow. In addition, some strains secrete bactericidal substances, which makes the implantation of external agents even more difficult.

Summary

Fascinating, isn't it? In the end, it turns out that bacteria and the human being are indivisibleThey are often associated with diseases and infectious processes, however much they may be. In any case, some of the data reported should be taken with some reserve, since it is clear that it is not the same to investigate bacterial action in a human being or in a mouse (although the former would be illegal and ethically unfeasible).

Despite the limitations in the field of research, everything indicates (and we can affirm) that intestinal flora is essential for our survivalWe can say that our intestinal flora is essential for our survival, since several bacterial metabolic processes have been clearly and irrefutably recorded in our species. Without our gut bacteria, we are nothing.

Bibliographical references:

• Farias, M. M., Silva, C., & Rozowski, J. (2011). Gut microbiota: role in obesity. Revista chilena de nutrición, 38(2), 228-233.
• Guarner, F. (2002). The colon as an organ: habitat of bacterial flora. Nutr Hosp, 17(Sup 2), 7-10.
• Guarner, F. (2007). Role of intestinal flora in health and disease. Hospital Nutrition, 22, 14-19.
• Icaza-Chávez, M. E. (2013). Gut microbiota in health and disease. Mexican journal of gastroenterology, 78(4), 240-248.
• Mac Cormack, W. P., & Fraile, E. R. (1991). Bacterial flora of the digestive tract of specimens from. Revista Argentina de Microbiología, 23, 160-165.
• Sánchez Súarez, H., Fabián Domínguez, F., Ochoa Mogollón, G., & Alfaro Aguilera, R. (2019). Bacterial succession of the digestive tract of piglets fed biological silage. Journal of Veterinary Research of Peru, 30(1), 214-223.