Microbi care traiesc pe soric, in rat, in matze, in gura si in pizda

News of the Week SCIENCE
MICROBIOLOGY:
Bacteria Are Picky About Their Homes on Human Skin
Elizabeth Pennisi

Julie Segre is touring the microbial landscape of our body's biggest
organ, the skin. In anticipation of a $115 million, 5-year effort by
the U.S. National Institutes of Health (NIH), she's traveling from
head to toe, conducting a census of some of the trillions of bacteria
that live within and upon human skin. Although their project is just
getting off the ground, Segre, a geneticist at the National Human
Genome Research Institute (NHGRI) in Bethesda, Maryland, and her
colleagues have already uncovered a surprising diversity and
distribution among skin bacteria. And a few oddities have emerged,
too: Microbes known mostly from soils like healthy human skin, living
in harmony with us; and the space between our toes is a bacterial
desert compared to the nose and belly button.

Segre's work on what bacteria live where "is cool stuff," says Steven
Salzberg, a bio-informaticist at the University of Maryland, College
Park. "We need to increase our own and the public's awareness of the
diversity and quantity of bacterial species on our own skin. The more
people are aware, the more we can do to control infection."

Bacteria and other microbes that colonize our skin and other tissues
outnumber the human body's cells 10 to 1, forming dynamic communities
that influence our ability to develop, fight infection, and digest
nutrients. "We're an amalgamation of the human and microbial genomes,"
says Segre. Recognizing this, NIH last year designated the Human
Microbiome Project as one of its two Roadmap initiatives (Science, 2
June 2006, p. 1355). Researchers will sequence the genomes of about
600 bacteria identified as human inhabitants and get a handle on the
99% of bacteria that defy culturing but thrive in the skin, nose, gut,
mouth, or vagina. "You have to understand what is the normal flora in
the healthy skin to understand the impact of flora on disease," says
Kevin Cooper, a dermatologist at Case Western Reserve University in
Cleveland, Ohio.

As a first step, Segre, NHGRI postdoctoral fellow Elizabeth Grice, and
their colleagues have studied five healthy volunteers, swabbing the
insides of their right and left elbows. The site chosen isn't as
unusual as it sounds; people with eczema often develop symptoms there.
To survey the full thickness of skin, the researchers also used a
scalpel to scrape off the top cel ls. And to reach even deeper, they
took small "punches" of skin, a procedure akin to removing a mole.

From all the samples, Grice, Segre, and colleagues pulled out 5300 16S
ribosomal RNA genes, which vary from microbe to microbe. After lumping
together the most similar 16S genes, they came up with 113 kinds of
bacteria and identified these dermal residents by matching the 16S
genes to those of known bacteria. (Segre described the results at a
recent meeting at Cold Spring Harbor Laboratory, and they are being
published online 23 May in Genome Research.) "That's a lot of
diversity, a lot of different organisms," says Martin Blaser, a
microbiologist at New York University, who has done a similar survey
of microbes living on the forearm, also finding a lot of diversity.

Yet just 10 bacteria accounted for more than 90% of the sequences.
Almost 60% of the 16S genes came from Pseudomonas, Gram-negative
bacteria that flourish in soil, water, and decomposing organic debris.
The next most common one, accounting for 20%, was another Gram-
negative soil and water bug, Janthinobacterium. Neither had been
considered skin microbes before this census. Although there were some
differences among the volunteers in the microbes present, their elbows
did share a common core set of microbes, the group reports.

The three sampling methods yielded slightly different results, with
"punches" revealing a surprising number of bacteria under the skin--1
million bacteria per square centimeter compared with 10,000 from the
scrapes. "I would have thought under the skin there would be fewer,"
says Salzberg.

Segre and her team have also begun sampling 20 other skin sites,
including behind the ear and the armpit, from the bodies of
volunteers. Skin varies in acidity, temperature, moisture, oil
accumulation, and "different environments select for different
microbes," says Blaser. Bacteriawise, reports Segre, "no subsite is
identical."

Some researchers suspect that shifts in the makeup of skin microbial
communities activate the immune system to cause diseases such as
eczema. "If you know what the [healthy] flora is, then one strategy is
to recolonize the area with the right flora," says Cooper.
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