Close Look at Human Arm Finds Host of Microbes

By Rob Stein
Washington Post Staff Writer
Monday, February 12, 2007

Hold out your hand, with the palm facing skyward. Pull the sleeve of your shirt up to your elbow. Now take a look at the fleshy part of your arm, about halfway between your wrist and your elbow. What do you see?

Nothing, probably.

But that's not what Martin J. Blaser of New York University School of Medicine sees. With the help of the latest scientific tools, Blaser sees a complex, microscopic world teeming with a vast array of microorganisms.

"The skin is home to a virtual zoo," said Blaser, a microbiologist who last week published online the first molecular analysis of the bacteria living on one small patch of human skin. "We're just beginning to explore it."

The analysis revealed that human skin is populated by a diverse assortment of bacteria, including many previously unknown species, offering the first detailed peek at this potentially crucial ecosystem.

The work is part of a broader effort by a small coterie of scientists to better understand the microbial world that populates the human body. Virtually every orifice and the digestive tract are swarming with bacteria, fungi and other microbes. By some estimates, only one out of every 10 cells in the body is human.

"If nothing else, this should be a shot across the bow to the scientific community that says, 'Hey, don't you think we should be taking a closer look at this?' " said David A. Relman, a Stanford University microbiologist. "To me it's still surprising, humbling and shocking how little we truly understand about the makeup of the human microbial community."

Scientists suspect these microbes play important but poorly understood roles, assisting crucial bodily functions and potentially helping prevent or cause many diseases. One recent study found that obese people appear to have a unique mix of microbes in their guts, which could partly account for the obesity epidemic.

"This type of work is setting the stage for a second human sequencing project -- one that examines our microbiomes" -- the genes of the microbial communities populating our bodies -- Jeffrey I. Gordon of Washington University in St. Louis wrote in an e-mail. Gordon reviewed Blaser's paper for publication by the Proceedings of the National Academy of Sciences.

"The result of this human microbiome project will be a more comprehensive view of our genetic landscape and should provide insights about which of our 'human attributes' are derived from products of our microbial self," he said. "This could lead, in turn, to new ways of defining health, new ways for predicting disease predilection, and new ways for treating illnesses affecting various components of our body, including the skin."

Blaser decided to focus on the skin in order to begin to understand the microbial makeup of the body's largest organ. Similar studies have been conducted on the mouth, colon, vagina and other parts of the body.

"No one had really done modern work on the skin," Blaser said. "This is really the first attempt to do something like this."

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