Human Skin Alive With Bacteria, Especially The Forearm
The study, led by researchers at the National Human Genome Research Institute, Bethesda, Maryland, and published online on 29 May in the journal Science, revealed even more surprises.
For instance, they found that our skin probably holds as varied a range of bacteria as our guts, which houses from 500 to 1,000 species of germs, and that there are vast differences across the skin, with the forearm being the most prolific site (44 species on average) and behind the ears being the most barren (19 species on average).
After all those years of being told by our grandmothers to wash behind our ears we would have been better off washing our forearms!
Lead author and postdoctoral fellow at NHGRI, Dr Elizabeth Grice, said:
"Our results underscore that skin is home to vibrant communities of microbial life, which may significantly influence our health."
We already knew that germs that live in our bodies and on our skin outnumber or own cells by 10 to 1, but it is only recently that scientists have started to look at how diverse the range might be.
The traditional way is to swab volunteers and grow cultures from the samples in the labs. But this method favours those bacteria that grow well in labs.
Now, thanks to gene technology, a new way is available, scanning the RNA of the bacteria directly, and last year we saw the first result of such technology (the paper appeared in the 23 May issue of Science) where it was revealed that human skin was home to a wider range of bacteria than we thought. However, this current study is the first to compare bacterial ecosystems living on different areas of skin.
For the study, the NHGRI researchers analyzed ribosomal RNA from samples taken from 20 sites on human skin (some oily, some moist, and some dry) and classified the microbes according to their genomes. Colleagues from the National Cancer Institute (NCI) and the National Institutes of Health (NIH) Clinical Center also worked on the study.
Overall, the RNA analysis found bacteria belonging to 19 different phyla and 205 different genera, with diversity at the species level being much greater than the researchers were expecting.
They found about 1,000 species altogether, and this was mostly the same across all 10 volunteers. What they also discovered is that we tend to have the same bacteria in our noses, from person to person, and on our backs, and in fact the bacteria that lives under my arms are likely to be more similar to the ones that live under your arms than they are to those that live on my forearm.
To get the samples the researchers asked 10 volunteers to wash only with mild soap for a week, not bathe or shower for 24 hours after that and show up at the lab to give their samples. The researchers swabbed and scraped all over their skin, including the nostril, the navel and the "gluteal crease", which is often exposed when people wear low-slung hipster jeans.
The researchers also did a follow up with 5 volunteers and found little change in the makeup of the bacterial colonies over time.
Senior author Dr Julia A Segre from the NHGRI said:
"Our work has laid an essential foundation for researchers who are working to develop new and better strategies for treating and preventing skin diseases."
"The data generated by our study are freely available to scientists around the world. We hope this will speed efforts to understand the complex genetic and environmental factors involved in eczema, psoriasis, acne, antibiotic-resistant infections and many other disorders affecting the skin," she added.
Co-author Dr Maria L Turner, senior clinician in NCI's Dermatology Branch, said:
"We selected skin sites predisposed to certain dermatological disorders in which microbes have long been thought to play a role in disease activity."
The study has produced information that could be useful in the fight against methicillin-resistant Staphylococcus aureus (MRSA), a bacterium that can cause serious, and sometimes life-threatening, infections.
Scientists already knew that many people have colonies of S. aureus inside their noses, so the researchers looked to see if this bacterium might also be found elsewhoere on the body. They found that the crease of skin on the outside of the nose had the most similar range of microbes as that found inside the nose.
NHGRI's Scientific Director Dr Eric D Green, who co-authored the study, said:
"Not only does our work shed new light on understanding an important aspect of skin biology, it provides yet another example of how genomic approaches can be applied to study important problems in biomedical research."
"Topographical and Temporal Diversity of the Human Skin Microbiome."
Elizabeth A. Grice, Heidi H. Kong, Sean Conlan, Clayton B. Deming, Joie Davis, Alice C. Young, NISC Comparative Sequencing Program, Gerard G. Bouffard, Robert W. Blakesley, Patrick R. Murray, Eric D. Green, Maria L. Turner, and Julia A. Segre.
Science 324 (5931), 1190, published online 29 May 2009.
Sources: ScienceNOW Daily News, NIH/National Human Genome Research Institute .
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