ABSTRACT
The human body is covered with trillions of bacteria collectively known as the human microbiome, which is separated into five distinct regions; oral, nasal, skin, vaginal, and gut. Each region contains its own unique abundance and diversity of microbes. The gut contains the most abundant microbiome community, consisting of approximately 100 trillion microbes, outnumbering the cells of the human body 10 to 1 and containing more than 1000 different bacterial species and 10 times the genes of the human genome. The four main phyla of bacteria that populate the human gut are Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria with the two primary phyla being Firmicutes and Bacteroidetes. The human gut microbiome is established during infancy and contains a diverse and dynamic community of microbes that serves numerous important functions. These include the metabolism of otherwise indigestible polysaccharides that impact energy harvest and storage, the modulation of the host immune system, and protection from pathogens through gut barrier defense. Given the critical functions of the gut microbiota in the human body, any deviation in microbial composition that leads to impairments of these functions can drastically compromise host health. Alteration of the early infant gut microbiome has been correlated with the development of childhood obesity and autoimmune conditions, including asthma, allergies, and, more recently, type 1 diabetes. This is likely due to complex interactions between the mode of delivery, antibiotic use, maternal diet, components of breast-feeding, and a network of regulatory events involving both the innate and adaptive immune systems within the infant host. The main approach to studying changes in the composition of the intestinal microbiota in relation to obesity has relied primarily on the phylogenetic characterization of the microbiota of diseased individuals in comparison with apparently healthy individuals. More recently, strong evidence supporting a role for commensal bacteria on mammalian host metabolism has accumulated based on the biochemical and physiological characteristics of germ-free (GF) mice following their colonization with human microbes from obese adults. However, there are substantial interindividual and intraindividual variations in the composition of the intestinal microbiota that occur during the first 2-3 years of life, making it
Introduction .................................................................................................................................... 235 Possible Mechanisms by Which the Gut Microbiome Contributes to Obesity .............................. 236 Events That Impact Early Development of the Microbiome ......................................................... 237 Impact of Early Colonizers on Infant Health ................................................................................. 239 Conclusion ..................................................................................................................................... 239 References ...................................................................................................................................... 239
difficult to establish precise cause-effect relationships between human health and the presence and relative abundance of specific microbial communities [1].
