Figure 1.

Stages of microbial colonization of the infant and child intestine. Most abundant bacterial families are depicted in circles, where the size of the circle is proportional to the relative abundance of the bacterial taxa at each growth stage. The intestinal microbiota of the newborn is initially colonized by Enterobacteria. In the days after, strict anaerobic bacteria dominate the microbial community. During the first month, bifidobacterial species predominate in the gut, but the introduction of solid foods at around 4–6 months is accompanied by an expansion of clostridial species (Lachnospiracea, Clostridiaceae, and Ruminococcaceae). Members of the Ruminococcaceae family continue to increase in abundance in the following months. By 2–3 years of age, the microbiota composition consists of mainly Bacteroidaceae, Lachnospiraceae, and Ruminococcaceae, which then remains stable into adulthood.