May 29, 2009

Surprising Variety Of Microbes Live On Human Skin

Symbiosis between humans and bacteria has been a long accepted and heavily studied phenomenon of human physiology. 

New studies of human skin, however, are revealing a previously little understood facet of biological interdependence between us and the microscopic inhabitants of our body.

Scientists from the National Institutes of Health recently set out to explore the micro-ecosystem living on the surface of our skin.  Preliminary results from the study have revealed an unexpectedly diverse fauna of bacteria and microbes, and a far more intricate and complex system of life than previously thought.

The study also revealed that the diversity of microorganisms inhabiting different regions of the body are largely specific to those body parts, even across different people.  For example, the microbes inhabiting your armpits are far more similar to those inhabiting another person's armpit than they are to the bacteria that live between your toes.

"Our work has laid an essential foundation for researchers who are working to develop new and better strategies for treating and preventing skin diseases," said the study's lead author Julia A. Segre Ph.D. of the National Human Genome Research Institute (NHGRI).

"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 explained.

Employing the most modern DNA sequencing technology rather than traditional methods of growing laboratory cultures, Segre's research team uncovered a far more diverse array of microorganisms on the human epidermis than previous studies had indicated.

For the study, the scientists took skin samples from 20 different sites on the body from 10 healthy subjects.

"We selected skin sites predisposed to certain dermatological disorders in which microbes have long been thought to play a role in disease activity," explained Maria L. Turner, M.D., a co-author of the study.

The scientists then extracted DNA from each of the samples and sequenced the gene that codes for the 16S ribosomal RNA, a sequence of DNA found only in bacterial cells.  The analysis revealed over 112,000 different bacterial gene sequences, representing 19 different bacterial phyla and 205 different genera.

The researchers also assayed the degree of variety found in different areas of the body. 

They found that the skin on the forearm displayed the greatest biological diversity, with an average of 44 different bacterial species, while the area behind the ears showed the smallest variety, with an average of 19 different species.

The research team also classified different sampled body regions into three main categories of microenvironments: oily (such as beside the nose and between eyebrows), moist (inside nose and armpits) and dry (inside of forearm and buttocks).  They found that found that the dry and moist areas exhibited a far greater variety than did oily areas.

"Our results underscore that skin is home to vibrant communities of microbial life, which may significantly influence our health," summarized study co-author, Elizabeth Grice, Ph.D.

NHGRI's Scientific Director and study participant Eric D. Green, M.D. added, "[n]ot 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."

"This also demonstrates what can be achieved through efforts that pull together researchers from across NIH."

The NIH Clinical Center recently began working on the Human Microbiome Project, an orchestrated effort to map out the different microbial communities inhabiting different parts of the human body and to research how these fauna change in instances of disease. In addition to skin and nose, that project will also be analyzing microbes in the digestive tract, the mouth and the vagina.


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