Germs Mingle Most on Palms, Feet, Forearms

THURSDAY Nov. 5, 2009 -- A new "atlas" of bacterial life on and within the human body has uncovered the fact that your palms, feet and forearms are a veritable United Nations of germs.

The scientists, using sophisticated gene-sequencing technologies, pinpointed specific bacterial types and where they like to thrive on and within the body. They found a wide variability of bacteria, depending on the spot on the body. They also found that bacterial colonies differed person to person, with each individual carrying his or her own "personalized" assortment of microorganisms.

"We've always known that there are microbes on us and in us," said study author Noah Fierer, an assistant professor of microbial ecology at the University of Colorado at Boulder. "But we weren't always able to isolate them and differentiate them from each other. With these new techniques, we can."

"Each of us is really an archipelago of distinct habitats, at least as far as bacteria are concerned," added senior study author Robert Knight, an assistant professor of chemistry and biochemistry and computer science at the University of Colorado. "It's truly amazing how different the sites within the same body are, and how different the corresponding sites on different people are."

The team's work is being published Nov. 5 in the online version of Science. The study builds on earlier research, including a 2008 study that found that women had a greater diversity of bacteria on their palms than men.

The mapping project focused on seven to nine men and women, who were examined four times each over a three-month period. Researchers swabbed 27 different sites, searching for bacteria in virtually every nook and cranny, from hair to ear wax, mouth to nostril and trunk and legs.

So, where are the most popular places for bacteria to hang out? They seem to like the gut (no surprise there), forearms, palms, index fingers, the backs of the knees and soles of the feet, according to the study. At least that is where some of the most diverse and thriving colonies take root.

Some bacterial communities appeared to strongly prefer one body spot over another. For example, when the scientists transplanted microbial groupings from the forearm to the forehead, the germs failed to thrive. But doing the reverse -- transplanting communities from forehead to forearm -- didn't seem to impede bacterial growth.

Researchers focused on bacterial diversity rather than bacterial quantity. There are thousands of bacterial types, but certain ones seemed prominent in the study, said Fierer. Four bacterial groups stood out -- Actinobacteria, Firmicutes, Proteobacteria and Bacteroidetes -- and they were relatively stable over time. Individual bacterial types included the Streptococcus and Staphylococcus bacteria.

In some ways, the mapping efforts spurs more questions than it answers. Researchers are not sure why the forearms and other body parts attract so much microbial diversity. Also, it is not clear whether the different strains compete with each other or live in a kind of bacterial harmony.

Researchers also want to know whether people are born with these bacterial colonies or develop them after birth, through external contact with their mothers and during the delivery process. Even more fascinating is why each person has his or her own blend of bacteria -- much like a fingerprint. Perhaps diet, climate, locale or a combination of variables are responsible for each person's unique bacterial make-up, said Fierer.

Most important, researchers want to know how the colonies impact health and whether they can be harnessed in some way to treat disease. In the future, for example, microbial mapping could lead to routine screening of patients as a way to record a baseline of their normal microbial communities. Any later deviation could be a sign of disease.

"Our ultimate goal is to devise strategies for personalized medicine, based not on the human genome, where we are all 99.9 percent identical, but on the human microbiome, where we are 80 to 90 percent different from one another," added Knight.

More information

There's more on the biology and health-care potential of microbial communities at the U.S. National Institutes of Health.

Posted: November 2009


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