Development of gut microbiota in infants not exposed to medical interventions.

Knowledge of the composition of a normal healthy gut microbiota during infancy is important for understanding the role of gut microbiota in disease. A limitation of previous studies is that they are based on infants who have been subject to factors, which can have a profound disruptive effect on the natural colonization process. We describe the colonization process, during the first 4 months after birth, in 85 infants who have experienced no major medical or dietary interventions. They were all vaginally delivered, healthy, term infants, who were not exposed to antibiotics, exclusively breastfed during their first month of life and at least partially breastfed up to 4 months. Selected microbial groups were identified by targeting small subunit microbial ribosomal RNA genes. In contrast to more recent studies, but in agreement with older studies, almost all our infants harbored γ-Proteobacteria and Bifidobacterium. Yet undefined non-cultivable species belonging to Bacteroides, as well as microbes identified as Lachnospiraceae 2, were common. Strong associations were observed between some specific constituents of microbiota at day 4 and the concentration of specific microbial groups at day 120, indicating that early gut microbiota may influence later microbiota. Novel information of the undisturbed composition of early gut microbiota in babies is presented.