<P> Further studies have indicated a large difference in the composition of microbiota between European and rural African children . The fecal bacteria of children from Florence were compared to that of children from the small rural village of Boulpon in Burkina Faso . The diet of a typical child living in this village is largely lacking in fats and animal proteins and rich in polysaccharides and plant proteins . The fecal bacteria of European children was dominated by Firmicutes and showed a marked reduction in biodiversity, while the fecal bacteria of the Boulpon children was dominated by Bacteroidetes . The increased biodiversity and different composition of gut flora in African populations may aid in the digestion of normally indigestible plant polysaccharides and also may result in a reduced incidence of non-infectious colonic diseases . </P> <P> On a smaller scale, it has been shown that sharing numerous common environmental exposures in a family is a strong determinant of individual microbiome composition . This effect has no genetic influence and it is consistently observed in culturally different populations . </P> <P> In humans, a gut flora similar to an adult's is formed within one to two years of birth . The gastrointestinal tract of a normal fetus is considered sterile, but microbial colonisation may occur in the fetus and Lactobacillus and Bifidobacterium species were present in placental biopsies in one study . During birth and rapidly thereafter, bacteria from the mother and the surrounding environment colonize the infant's gut . As of 2013, it was unclear whether most of colonizing arise from the mother or not . Infants born by caesarean section may also be exposed to their mothers' microflora, but the initial exposure is most likely to be from the surrounding environment such as the air, other infants, and the nursing staff, which serve as vectors for transfer . During the first year of life, the composition of the gut flora is generally simple and it changes a great deal with time and is not the same across individuals . </P> <P> The initial bacterial population are generally facultative anaerobic organisms; investigators believe that these initial colonizers decrease the oxygen concentration in the gut, which in turn allows purely anaerobic bacteria like Bacteroides, Actinobacteria, and Firmicutes to become established and thrive . Breast - fed babies become dominated by bifidobacteria, possibly due to the contents of bifidobacterial growth factors in breast milk, and by the fact that breast milk carries prebiotic components, allowing for healthy bacterial growth . In contrast, the microbiota of formula - fed infants is more diverse, with high numbers of Enterobacteriaceae, enterococci, bifidobacteria, Bacteroides, and clostridia . </P>

Where does our first normal flora come from