The interpersonal and intrapersonal diversity of human-associated microbiota in key body sites

The human body harbors 10 to 100 trillion microbes, mainly bacteria in our gut, which greatly outnumber our own human cells. This bacterial assemblage, referred to as the human microbiota, plays a fundamental role in our well-being. Deviations from healthy microbial compositions (dysbiosis) have been linked with important human diseases, including inflammation-linked disorders, such as allergies, obesity, and inflammatory bowel disease. Characterizing the temporal variations and community membership of the healthy human microbiome is critical to accurately identify the significant deviations from normality that could be associated with disease states. However, the diversity of the human microbiome varies between body sites, between patients, and over time. Environmental differences have also been shown to play a role in shaping the human microbiome in different cultures, requiring that the healthy human microbiome be characterized across life spans, ethnicities, nationalities, cultures, and geographic locales. In this article we summarize our knowledge on the microbial composition of the 5 best-characterized body sites (gut, skin, oral, airways, and vagina), focusing on interpersonal and intrapersonal variations and our current understanding of the sources of this variation.