Intestinal microbiota and its functions

The digestive tract harbours the largest and most complex microbial community of the human body, the intestinal microbiota, including about 800 different bacteria species. The distribution of this microflora is uneven, with highest concentrations in the colon. Bacterial colonization of human gut by environmental microbes, beginning immediately after birth, becomes more complex with increasing age, with a high degree of variability among human individuals. The gastrointestinal tract is the main site where environmental microorganisms and antigens interact with the host, through intensive cross-talks. Gut microbiota is essential for intestinal development, homeostasis and protection against pathogenic challenge; moreover, gut microbes are involved in metabolic reactions, with harvest of energy ingested but not digested by the host; they have also trophic effects on the intestinal epithelium, by favouring the development of intestinal microvilli, and play a fundamental role in the maturation of the host's innate and adaptive immune responses.