[The colon as an organ: habitat of bacterial flora]

The intestinal flora constitutes a complex ecosystem comprising several hundred species of micro-organism, most of them in the genus bacteria. This ecosystem includes some micro-organism considered to be pathogenes for their capacity to invade the host, but they also contain numerous species capable of promoting beneficial effects on health. Bacterial flora begins to be acquired inmmediately after birth. By the age of two years, the flora etablished is practically definitive. There are transiet modifications derived from the use of antibiotics or in connection with changes in diet, but these are normally reversible so that every individual tends to have a relatively stable flora. The composition of bacterial flora varies from one individual to another but it is metabolic functions show less diversity. The flora in the human colon is like an organ with intense metabolic activity due to the action of bacterial enzymes on the substrates present in the intestine. Many authors have considered it more relevant to identify the enzymatic activity of the bacterial flora than the variety of species contained. The main function of the flora are: 1) fermentation of dietary waste and endogenous mucins; 2) energy recovery through the generation of short-chain fatty acids; 3) protection against colonization and invasion by pathogens (barrier effect), and 4) development, stimulation and modulation of the immune system. Special attention has been paid in recent years to the recognition of certain bacterial species that can have such salutary effects on the host. Probiotics are living microorganism that are consumed in order to obtain a beneficial effect regardless of their intrinsic nutritional value. Considerable experimental evidence has been gathered to suggest that probiotics are useful in many health-related spheres. There is good documentation to the effect that the consumption of yoghurt reduces the signs and symptoms of intestinal lactase deficiency. Some probiotics have been shown to be useful in the prevention and treatment of acute diarrhoea due to rotavirus in children and adolescents. The consumption of certain probiotics has also been seen to reinforce certain functions in the human immune system.