Microbial zoo

Viruses, bacteria and fungi abound in healthy people

Enterococcus faecalis
U.S. Department of Agriculture/Eric Young

The bacterium Enterococcus faecalis, which lives in the human gut, is just one type of microbe studied as part of the Human Microbiome Project funded by the National Institutes of Health (NIH).

Trillions of microbes inhabit the human body, occupying virtually every nook and cranny. And most of the time, this relationship is a friendly one, with microbes helping to digest food, strengthen the immune system and ward off dangerous pathogens.

But despite microbes’ prominent roles, researchers have understood little about which of them reside in specific sites of the body. Now, a consortium of some 200 U.S. scientists reports findings from the most comprehensive census of the microbial makeup of healthy humans. 

The research, published June 14, 2012, in Nature and in several Public Library of Science (PLoS) journals, offers new details and even some surprises.

For example, the researchers found that even healthy people typically carry low levels of harmful bacteria in and on their bodies. But when a person is healthy, these pathogens don’t cause disease; they simply coexist in an abundance of beneficial microbes. Now, scientists can investigate why some pathogens suddenly turn deadly, which will refine current thinking on how microorganisms cause disease.

Scientists identified more than 10,000 species of microbes that occupy the human ecosystem, documenting the impressive diversity of microbial life in the human body.

“It’s not possible to understand human health and disease without exploring the massive community of microorganisms we carry around with us,” says George M. Weinstock, PhD, associate director of The Genome Institute at Washington University and one of the project’s principal investigators. “Knowing which microbes live in various ecological niches in healthy people allows us to better investigate what goes awry in diseases that are thought to have a microbial link, like Crohn’s and obesity, and why dangerous pathogens sometimes, but not always, cause life-threatening illnesses.”

Washington University and its Genome Institute played a major role in the research, known as the Human Microbiome Project. The five-year initiative was funded with $153 million from the National Institutes of Health (NIH), with some $32 million coming to Washington University.

Genome Institute scientists decoded about half of the 5,000 specimens from nearly 250 healthy volunteers.

“Data generated from this study has the added potential to provide scientists with new insights into how local environments shape the composition of microbes that are found in healthy individuals,” says co-investigator Mark A. Watson, MD, PhD, associate professor of pathology and immunology.

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