The Gut Microbiome in Health and in Disease

Andrew B. Shreiner; John Y. Kao; Vincent B. Young


Curr Opin Gastroenterol. 2015;31(1):69-75. 

In This Article

Structure and Dynamics of the Healthy Adult Microbiota

Characterization of the microbiome in healthy individuals is an important initial step in understanding the role of the microbiome in contributing to health and disease. Healthy adult humans each typically harbor more than 1000 species of bacteria belonging to a relatively few known bacterial phyla with Bacteroidetes and Firmicutes being the dominant phyla.[9] The microbiota of the gut is quite diverse (Table 1) compared to other body sites, and there is considerable variation in the constituents of the gut microbiota among apparently healthy individuals.[10] As a way of accounting for the microbial variability among healthy individuals, researchers have tried to identify certain stable patterns of microbial populations in the human population.[11] Data from the HMP was used to identify community types at different body sites on the basis of statistical analysis of the configuration of multiple bacterial taxa.[12] Four distinct communities were found in the stool, and metadata factors associated with community types included breastfeeding, gender, and education. Interestingly, community types in the oral cavity were predictive of those in the stool though the specific constituents were different. In a recent study[13] of 37 healthy American adults not taking antibiotics, greater than 70% of fecal bacterial species within an individual were stable over 1 year, and few additional changes were measured out to 5 years. Calculations showed that species were likely stable over decades if not for an individual's entire lifetime as evidenced by species shared with adult family members but not with unrelated individuals. Although we have gained a deep understanding of the structure and dynamics of the microbiome in healthy humans, this effort is complicated by significant variability in the population, modest variability over time within an individual, and uncertainty over the most meaningful ways to characterize the microbiota.