U.S. Department of Health and Human Services

People Host Communities of Microbes

The Human Microbiome – Bacterial “Census” Reveals that Healthy People Host Distinct Communities of Microbes

Researchers have developed a catalogue of the diversity and variation in bacterial species that reside on or within the body of healthy people. The human body is host to an enormous ecosystem of microorganisms. This microbial community—or microbiota—contains nearly 100 trillion organisms, with the number of bacterial cells on or in the human body outnumbering human cells by almost ten to one. The resident bacterial communities provide important functions that aid in metabolism, help prevent infections, and train the immune system. Since these traits are critical for normal health and may, if altered, contribute to disease, it is important to understand the diversity and variation of the human microbiota at different body sites, among individuals, and over time. Although previous studies revealed the diversity of the bacterial communities residing at distinct body sites, an integrated view of the human microbiota across the entire body is needed to fully define the genetic diversity that contributes to normal health.

Using state-of-the-art DNA sequencing methods, researchers have taken a census of the bacterial communities across several body sites of healthy individuals. The researchers collected samples of the bacterial communities from different body sites—including the gut, mouth, ears, nose, hair, and various skin surfaces—of healthy volunteers on several occasions over a three-month period. After isolating the bacterial DNA from these samples, the scientists analyzed the DNA sequences of a particular gene known to vary among different bacterial species to determine the diversity of bacterial species present at different sites for each individual. They found that the composition of the bacterial communities was determined mostly by their location on or in the body, with the different body sites having distinct community members. These communities were dominated by four groups of related bacteria, with no one particular group found on all of the body sites of any individual on any given day in this study. In addition, the bacterial community composition at some body sites, such as in the gut, varied considerably between different people. However, each individual’s “personalized microbiota” appeared to be relatively stable over time. By defining the composition and variation of the microbiota in healthy individuals, researchers now have a baseline for detecting changes in the microbiota that may be associated with human diseases.
Costello EK, Lauber CL, Hamady M, et al. Bacterial community variation in human body habitats across space and time. Science 326: 1694-1697, 2009.