Intestinal flora: what it is, features and functions

Bacteria are unicellular prokaryotic microorganisms (formed by a cell without a nucleus) with a size of up to 5 micrometers and an immense variety of shapes and aggregations.

How they are invisible to the human eye without the methods of microscopy, we often neglect the importance of these microorganisms at the biological levelBut nothing could be further from the truth: the total biomass of the planet is estimated at 550 gigatons, of which 15% correspond to bacteria.

Just to give you an idea, the amount of carbon present in animals is 2 gigatons in total, 35 times less than the biomass supplied by these microorganisms. Understanding an ecosystem without bacteria is impossible, as homework ranges from participating in the natural cycles of elements such as nitrogen, carbon and phosphorus, to transforming organic substances into inorganic substances and vice versa. Simply, without bacteria, there would be no life.

Beyond an ecosystem or a global scale, it is striking to discover that our own body would not maintain itself without bacterial action either. Today we come to talk about the microbiome present in humans, more precisely, intestinal flora.

    What is the microbiome?

    We generally refer to the set of bacteria that inhabit our body as the “intestinal flora”. This is a mistake, because these microorganisms have nothing to do with all the plants in a geographic region. While we maintain this terminology for awareness purposes, it is important that you know that the correct term is microbiome.

    The microbiome (or normal microbiota) refers to the set of microorganisms that are generally located in different places in the body of multicellular organisms., How does 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, genitals, intestines, and many other areas.

    The microbiota, depending on its dependence and length of stay in humans, can be classified into several types. We tell you briefly:

    • Native microbiota: those microorganisms that colonize humans for a prolonged period. They are symbiotes because they have co-evolved with us.
    • Allochthonous microbiota: They don’t need us, so they are found in other habitats beyond the human body. They temporarily occupy our microbiome.
    • Latent microbiota: which is present for (almost) the entire life of the host. Their populations do not fluctuate drastically unless pathologies appear.
    • Transient microbiota: its population fluctuations are continuous, so it follows that these bacteria are not essential for the host.

    What is the intestinal flora?

    Based on the terms previously described, we can define intestinal flora as all the microorganisms in a defined environment, in this case the digestive tract. Due to their proximity to humans and the symbiotic work with our body, we can say that most of the bacterial colonies that we will name are native and latent, that is, indivisible to the gastric functioning of our species.

    Each adult human being has around 100 trillion bacteria in their body, representing around 400 different species.. While the presence of these microorganisms is not very high in the stomach due to the presence of acids, as we progress through the gastrointestinal tract the thing becomes more interesting.

    For example, the concentration of bacteria increases along the small intestine, from 10 ^ 4 bacteria / ml in the proximal duodenum to 10 ^ 7 bacteria / ml in the terminal ileum. In total, the bacterial population in the colon can add up to 600 grams in weight, making up over 95% of the host’s total microbiome. Incredible numbers, right?

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

      What species are found in the intestinal flora?

      The composition of the intestinal flora in humans is very variable, As it depends on location, diet, age and many other factors. However, several studies have proposed, by consensus, 3 predominant sections in this type of microbiome:

      • Firmicutes (65%): This cut represents over 200 bacterial genera in the intestines, the most important of which are Mycoplasma, Bacillus and Clostridium.
      • Bacteroids (23%): a large group of gram-negative anaerobic bacteria.
      • Actinobacteria (5%): it is interesting to note that they are the sections most represented in soils. 64% of the bacterial biomass of the substrates corresponds to species of actinobacteria.

      On another side, at the metabolic level, they are divided into 3 different groups: Producers of lactic acid, responsible for rot and others.

      The microbiota belongs to everyone, so it’s impossible to generalize beyond this list. At birth, the intestine is sterile, but colonizes completely during the first year of life. From here, fluctuations occur between individuals depending on the type of breastfeeding, genetic contribution, diet, environmental factors and an almost endless list of variables.

      The functions of the gut microbiome

      We’ve told you over and over that the gut microbiome is essential for the well-being of the body, but why? In the following lines, we give you answers.

      1. Metabolism

      While it might not seem like it at first glance, the intestines are one of the most immune areas in the whole body. For that, immune responses are partially modulated by the intestinal flora because, among other things, it allows energy savings through the fermentation of carbohydrates, the synthesis of vitamins B and K and the production of short-chain fatty acids, among others.

      In addition, symbiotic colonies of microorganisms stimulate intestinal development, maintain epithelial renewal, modulate the immune response and participate in the metabolism of certain drugs. Without a doubt, its functions at the metabolic level are invaluable.

      2. Prevention of obesity and diabetes

      Although it is necessary to take these results with tweezers, it has been shown in experimental environments, mice without germs 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 of people with a standard body mass index, but the causality between the two events has not yet been fully confirmed.

      3. Increased use of food

      As we said in the previous lines, some bacteria produce enzymes capable of breaking down molecules that we humans cannot digest on their own, such as cellulose, hemicellulose and pectin.

      After certain metabolic reactions, these compounds of plant 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 calorie intake of an adult human.

      4. Antibacterial action

      Symbiont bacteria in the intestinal tract occupy an ecological niche they don’t want to get rid of, so 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 room to develop. In addition, some strains secrete bactericidal substances, which makes implantation of external agents even more difficult.


      Fascinating, isn’t it? In the end, it turns out that bacteria and humans are indivisibleNo matter how often they are associated with diseases and infectious processes. Either way, some of the reported data should be taken with some caution, as it is clear that the investigation of bacterial action in humans or in mice is not the same (although the first would be illegal and ethically impractical).

      Despite the limitations of the field of research, everything indicates (and we can say) that intestinal flora is essential for our survivalSince then, several bacterial metabolic processes have been recorded in our species in a clear and compelling manner. Without our gut bacteria, we are nothing.

      Bibliographical references:

      • Farías, MM, Silva, C. and Rozowski, J. (2011). Intestinal microbiota: role in obesity. Chilean Journal of Nutrition, 38 (2), 228-233.
      • Guarner, F. (2002). The colon as an organ: habitat for 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, ME (2013). Gut microbiota in health and disease. Journal of Gastroenterology of Mexico, 78 (4), 240-248.
      • Mac Cormack, WP and Fraile, ER (1991). Specimens of bacterial flora of the digestive tract. Argentine Journal of Microbiology, 23, 160-165.
      • Sánchez Súarez, H., Fabián Domínguez, F., Ochoa Mogollón, G., and Alfaro Aguilera, R. (2019). Bacterial succession of the digestive tract of piglets fed on organic silage. Journal of Veterinary Research of Peru, 30 (1), 214-223.

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