Abstract

Early acquisition of a healthy infant microbiota are a key determinant in the maturation and function of the immune system. Healthy microbiota, described as having a diverse composition with high counts of Bifidobacteria and low counts of Clostridium difficile and E. coli is often identified in term infants, born vaginally, and exclusively breast-fed. In contrast, early lifeevents such as birth by Caesarean section, feeding of formula, and antibiotic treatment hinder the establishment of a healthy balance of intestinal flora. These events, which are associated to altered microbiota composition, have also been associatedwith various immunologic related diseases of infancy and childhood, particularly atopic disease. Increasingly, associations have also been made between certain microbiota profiles in individuals with functional and inflammatory bowel disease, as well asadult obesity. This mounting evidence is suggestive of the significant role that bacterial-host interactions play in maintaining hosthealth in early life, and potentially beyond.