It is called intestinal flora and biota to all bacteria living in the gut, in a symbiotic relationship type as both commensal and mutualism. This set is part of the normal microbiota. The vast majority of these bacteria are not harmful to health, and many are beneficial. It is estimated that the human being has within 2,000 different species of bacteria, of which only 100 can become harmful. Many animal species depend closely on their intestinal flora. For example, without it, the cows would not be able to digest cellulose or termites feed on wood, as they are not themselves, but their intestinal flora, the ones capable of porcessing these foods.

In humans, the dependence is not as radical, but it is important. Sometimes they help with the absorption of nutrients and form a complex ecosystem that regulates and maintains balance by itself. At other times they are essential for the synthesis of certain compounds such as vitamin K and some B complex. It also has some side effects, such as gas production responsible for the characteristic odor of feces. Some of them can cause infections of any severity. Adult intestinal flora is influenced by a number of intrinsic (intestinal secretions) and extrinsic factors (aging, diet, stress, food antibiotics and prebiotics or probiotics components)

The intestinal flora, being composed of microorganisms, is very sensitive to antibiotics and these are the main cause of their destruction.

The intestinal flora prevents diseases to develop.


In the intestine of newborn infants there are no microorganisms. This causes among other things vitamin K deficiency that occurs endogenously only in the bowel thanks to these bacteria. Therefore, the application of an initial dose of vitamin k in neonates is needed. During the early stages of life a type of initial flora is composed, primarily from the vaginal and gastrointestinal flora of the mother. Subsequently, by effect of breast milk, a predominance of bifidobacteria in well-fed infants and diverse flora in those receiving other foods are favored. And finally, after weaning, a transition flora is produced which changes to adult flora.


Intestinal microbiota has been associated by various studies as some carbohydrate metabolism, immune system specialization and control endothelial cell growth, especially the colon (colonocytes).

This last feature is very important for the control of cancer in this area, as bacteria when metabolize foods rich in fiber, loose butyric acid involved in the differentiation of the large intestine cells and induces apoptosis, which is important for the removal of  non-functional cells that may be carcinogenic and to mitigate inflammation.


Some types of intestinal flora have enzymes for carbohydrate digestion that are not found elsewhere in the body. Polysaccharides such as starch, sugars, some oligosaccharides and some sugar that our body does not absorb during metabolism, are digested by diverse bacteria hosted in the gut. As a result of this carbohydrate metabolism and it´s fermentation, gas and flatulence are produced with characteristic odor of feces.


The intestinal flora has an important role in the specialization of the lymphoid tissue associated with the intestinal mucosa. These bacteria are responsible for showing the lymphocytes (T cells specifically) strains which are useful for the body and which are not, allowing them to recognize better the invading antigens. Thus, the bacteria hosted in the gut specialize the immune system to promote survival that decides which bacteria will be the dominant of the microbiota. This is one of the reasons why feeding should be ver well controlled in newly borns, since the first bacteria to be staying in the intestine will be adapting their microenvironment to promote their own survival, and this could affect the implementation of other essential bacteria in normal human microbiota.



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