It's a jungle on there: skin samples contain rich diversity of bacteria: inventory identifies body's most microbe-varied locales

Science News, Dec 6, 2008 by Tina Hesman Saey

PHILADELPHIA -- Most people think of rain forests as hot spots for biological diversity, but new research suggests that belly buttons are also rich ecosystems. That's one finding from the first attempt to take a large-scale inventory of microbes on human skin.

In recent years scientists have come to appreciate people as super organisms, composed not just of human tissue, but also of microbes galore. Human skin is covered by a variety of bacteria, viruses, fungi and mites, says Elizabeth Grice of the National Human Genome Research Institute in Bethesda, Md. Most of the time, people and their microbes live in harmony, but people with skin conditions such as eczema often struggle with skin infections.

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"The skin is two square meters of ecosystem," Grice said November 13 at a meeting of the American Society of Human Genetics.

Grice presented work she and her colleagues have done to catalog the diversity of bacteria living on human skin. The findings could help doctors and scientists better understand why some people develop skin conditions such as eczema and psoriasis while others with similar genetic backgrounds do not.

"We know there is a genetic component" to eczema, says Kimberly Chapman of the Children's Hospital of Philadelphia, who was not involved in the research. Some people with eczema have a defect in filaggrin, a protein that helps form the skin's protective barrier. But not everyone who has the filaggrin variation will get eczema. The new inventory of bacteria could help researchers determine whether people with eczema have an overactive immune response to bacteria living on their skin, Chapman says.

In the new study, dermatologists collected skin scrapings from 21 places on the bodies of 10 healthy volunteers. Grice and her colleagues examined genetic diversity in the 16S ribosomal RNA gene in bacteria in the samples. Scientists can use variations in this gene to distinguish one type of bacteria from another, and the technique has been used to sample bacteria living in oceans, human and mouse intestines, and even on shower curtains and toothbrushes.

Among the most diverse spots were the belly button, inner forearm, buttocks, the skin between the fingers and the gluteal crease (also known as the plumber's crack). Other body parts had a relative dearth of bacterial diversity. Cold spots were the greasy spot just behind the ear, the crease on the side of the nose, the toe webs and the sternum.

A few spots on some volunteers had up to 300 different species of bacteria, Grice says. Other areas contained as few as three types. The amount of diversity not only varied from body part to body part, but also from person to person.

The researchers plan to test the healthy volunteers again in six months and to recruit volunteers with eczema to see if they have different types of bacteria on their skin.