THE FORMATION AND THE STRUCTURE OF THE INTESTINAL MICROFLORA

Abstract

The bacterial population of the adult digestive tract consists mainly of two phyla: Bacteroidetes and Firmicutes. The formation of the intestinal microbiota covers a progressive evolution. In recent years, there is a widely held view that the bacterial colonization begins in utero. The presence of bacteria in the tissue of the placenta, in the foetal membranes, in the amniotic fluid and in the blood of the umbilical cord in healthy foetuses and newborns indicates the early exposure to the bacterial world as a first step of immune training. The colonization of the digestive tract continues and is amplified after birth. The vaginal birth induces an intestinal colonization that reflects the structure of maternal vaginal flora. The intestinal microbiota of C-section newborns is dominated by the maternal skin and oral flora but it also comprises the ecosystem of the skin of the medical personnel and the germs on the hospital surfaces. The breast milk contains live bacteria originating from the mammary canals, areola but especially from the maternal intestine, the latter being a natural source of colonization of the neonatal intestine. The physiological bacterial colonization of the intestine modulates gene expression of the epithelium for immune tolerance; it provides the host with nutrients and contributes to the maturing of the immune system.

Keywords

• intestine
• bacteria
• colonization
• immunity