Chinese Medical Journal
The digestive tract harbours the largest and most complex microbial community of the human body, the intestinal microbiota, including about 800 different bacteria species. 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.