The Intestinal Microbiota

microbiota intestinal

The intestinal microbiota, known until not so long ago as the intestinal flora, is the group or community of microorganisms that reside in an indigenous way in the entire gastrointestinal tract. The intestinal microbiota is part of all the microbiota that exist distributed practically all the organism since in addition to the intestine, there are also communities of microorganisms in other areas of the organism such as the skin, the mouth, the vagina, the respiratory tract, the genitourinary, in different mucous membranes, etc. although their quantity, compared to the intestine, is much smaller.

Size of the intestinal microbiota

In the case of the intestinal microbiota, the number of cells that compose it is approximately 1014, that is, about 100 trillion microorganisms, about 10 times more than the number of cells that make up our own body. This enormous quantity of microorganisms is distributed unevenly in the gastrointestinal tract so that the quantity increases as one advances through the entire digestive tract, the colon being the area where the greatest number of bacteria or microorganisms are concentrated. As a curious fact, all these bacteria together placed on a scale would weigh 1 kg and if we placed them one after another in a row, they could go around the world more than twice.

The Microbiome

Another closely related concept is that of intestinal microbioma. In this case the term microbiome refers to the genetic material, that is to say the set of genes that make up the microbial community or intestinal microbiota.

Life in symbiosis and functions of the intestinal microbiota

The intestinal microbiota lives in our organism in a symbiotic way, that is, these microorganisms that we have in the intestine live in a suitable environment for them from where they obtain their energy to live and in exchange produce metabolites that are necessary for the organism that it is incapable of producing.

In general, the intestinal microbiota exerts a protective function in the intestine by creating a hostile environment for other pathogenic microorganisms. In addition, they are also the producers of compounds that are necessary for the organism but which it is unable to produce, such as B or K group vitamins or some amino acids. Finally, the intestinal microbiota also produces short-chain fatty acids, especially butyric acid (and to a lesser extent acetic and propionic acid) which the body uses to obtain energy for the cells of the intestinal epithelium.

Development of the intestinal microbiota

The intestinal microbiota begins to form at the very moment of delivery, starting with the baby’s contact with the walls of the vaginal birth canal and the immediate contact with the outside world once outside the mother’s body. Later on, it is the mother’s milk, during lactation, which continues to provide microorganisms that will colonize the baby’s intestine.

At approximately 3 years of age, it is considered that the intestinal microbiota is practically formed, and furthermore, in a healthy child, in homeostasis, that is to say, in balance between the different species that make it up, since if it produces an imbalance, certain species may grow excessively and a pathogenic effect may occur due to this excessive increase. This is what is called intestinal dysbiosis, that is, the opposite of the mentioned homoeostasis.

Composition of the intestinal microbiota

It is currently known that the intestinal microbiota is composed of various types of microorganisms belonging to the following domains:

  • Bacterias
  • Arqueas
  • Eukaryotes: Mushrooms and Yeasts
  • Acytota

Within the domain of Bacteria, we can in turn find in the intestinal microbiota the following 5 phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria and Verrucomicrobria, of which the first two account for 90% of the total.

Among the best known species and with abundant presence in probiotic products are Lactobacillus, belonging to the phylum Firmicutes and Bifidobacterium belonging to the phylum Actinobacteria.

In the Eukaryotic domain and in its Ascomycota phylum, we also find another common probiotic, the Saccharomyces genus.


The functions performed by the intestinal microbiota are directly related to many diseases and pathologies (intestinal dysbiosis, irritable bowel syndrome, diarrhea of various origins, ulcerative colitis, etc.). Hence the importance of maintaining the microbiota in a state of balance or homeostasis and the great role played here by probiotics in order to readjust an altered microbiota and therefore its impact on the resolution of related pathologies.

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