But all palms contain 100 times the bacteria assumed, scientists say
TUESDAY, Nov. 4 (HealthDay News) -- Women's hands have a veritable United Nations of germs compared to men's, a new study finds.
But both genders house vastly more bacteria on their palms than previously suspected, according to a new study from University of Colorado researchers that appears in this week's issue of the Proceedings of the National Academy of Sciences.
The information may enable scientists to figure out what a "healthy" level of bacteria is, diagnose diseases more precisely, and perhaps even get advance warning that something is going wrong.
"The findings of the last few decades suggest that many diseases are due to many organisms, and it's the concerted change that leads to disease," noted Robert E. Marquis, a professor of microbiology and immunology at the University of Rochester Medical Center.
Microbes are one of the last frontiers for human exploration. In fact, the National Institutes of Health has initiated the Human Microbiome Project, with the objective of mapping human microbiota, most of which is currently unknown.
"With all the bacteria in the world, we probably know of less than 1 percent of them," Marquis said.
The technology used in this study, already used to study ocean waters, will help enable scientists to encounter the other 99 percent, he said.
The skin, particularly the palms of the hands, house thriving bacterial communities. To get a sense of the flora residing there, researchers scrutinized the palms of 51 undergraduate students for bacteria, just after the students had finished their academic exams.
A sampling of the entire DNA of microbes (known as metagenomics) revealed some 332,000 gene sequences, or about 100 times more than was found in previous studies of skin bacteria.
On average, each hand was home to about 150 different species of bacteria. Overall, more than 4,700 bacterial species were identified on all hands, only five of which were common among all volunteers.
Only 17 percent of bacteria types were shared between right and left palms, while volunteers shared just 13 percent of bacteria species with each other, probably due to "environmental" conditions, such as oil production, skin dryness, and what surfaces the hand had previously touched.
Skin bacteria was more diverse than bacteria found on the forearm or elbows or, indeed, other parts of the body including the mouth and gut.
Women had more germ diversity than men, possibly due to different acidities on the hands, different hand-washing regimens, differential production of sweat, variable hormones and how often moisturizers or cosmetics are applied.
In general, hand washing did not seem to affect the diversity of bacteria (though it's still a good practice, the researchers stressed). Either the bacteria come back quickly after hand washing (at least the kind of hand washing practiced by these volunteers) or hand washing just doesn't dislodge bacteria, they said.
The U.S. National Institutes of Health has more on the Human Microbiome Project.
SOURCES: Robert E. Marquis, Ph.D., professor, microbiology and immunology, University of Rochester Medical Center; Nov. 3-7, 2008, Proceedings of the National Academy of Sciences
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