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10,000 Germ Species Live In And On Healthy People

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By LAURAN NEERGAARD,AP Medical Writer

Thursday, June 14, 2012

WASHINGTON (AP) - They live on your skin, up your nose, in your gut - enough

bacteria, fungi and other microbes that collected together could weigh,

amazingly, a few pounds.

Now scientists have mapped just which critters normally live in or on us and

where, calculating that healthy people can share their bodies with more than

10,000 species of microbes.

Don't say " eeew " just yet. Many of these organisms work to keep humans healthy,

and results reported Wednesday from the government's Human Microbiome Project

define what's normal in this mysterious netherworld.

One surprise: It turns out that nearly everybody harbors low levels of some

harmful types of bacteria, pathogens that are known for causing specific

infections. But when a person is healthy - like the 242 U.S. adults who

volunteered to be tested for the project - those bugs simply quietly coexist

with benign or helpful microbes, perhaps kept in check by them.

The next step is to explore what doctors really want to know: Why do the bad

bugs harm some people and not others? What changes a person's microbial zoo that

puts them at risk for diseases ranging from infections to irritable bowel

syndrome to psoriasis?

Already the findings are reshaping scientists' views of how people stay healthy,

or not.

" This is a whole new way of looking at human biology and human disease, and it's

awe-inspiring, " said Dr. Tarr of Washington University at St. Louis, one

of the lead researchers in the $173 million project, funded by the National

Institutes of Health.

" These bacteria are not passengers, " Tarr stressed. " They are metabolically

active. As a community, we now have to reckon with them like we have to reckon

with the ecosystem in a forest or a body of water. "

And like environmental ecosystems, your microbial makeup varies widely by body

part. Your skin could be like a rainforest, your intestines teeming with

different species like an ocean.

Scientists have long known that the human body coexists with trillions of

individual germs, what they call the microbiome. Until now, they've mostly

studied those that cause disease: You may recall health officials saying about a

third of the population carries Staphylococcus aureus harmlessly in their noses

or on their skin but can infect others.

But no one knew all the types of microbes that live in healthy people or where,

and what they do. Some 200 scientists from nearly 80 research institutions

worked together for five years on this first-ever census to begin answering

those questions by unraveling the DNA of these microbes, with some of the same

methods used to decode human genetics. The results were published Wednesday in a

series of reports in the journals Nature and the Public Library of Science.

First, the researchers had to collect tissue samples from more than a dozen body

sites - the mouth, nose, different spots of skin, the vagina in women, and from

feces. Then they teased apart the bacterial DNA from the human DNA, and started

analyzing organisms with some daunting names: Lactobacillus crispatus,

Streptococcus mitis, Corynebacterium accolens.

Our bodies are thought to be home to about 10 bacterial cells for every human

cell, but they're so small that together microbes make up about 1 percent to 3

percent of someone's body mass, explained Dr. Green, director of NIH's

National Human Genome Research Institute. That means a 200-pound person could

harbor as much as 6 pounds of bacteria.

There are about 22,000 human genes. But the microbes add to our bodies the power

of many, many more - about 8 million genes, the new project estimated.

Those bacterial genes produce substances that perform specific jobs, some of

which play critical roles in the health and development of their human hosts,

said Dr. Bruce Birren of the Broad Institute of MIT and Harvard, another of the

project's investigators. Genes from gut bacteria, for example, lead to digestion

of certain proteins and fats. They also produce certain beneficial compounds,

like inflammation-fighting chemicals.

Another surprise: There isn't one core set of bacteria that perform those

functions. A wide variety can do the same jobs, the researchers found.

That's fortunate considering people carry a customized set of microbes, one that

varies dramatically depending on where you live, your diet and a host of other

factors. Your microbial zoos also can change, such as when taking antibiotics

that kill infection-causing germs as well as good intestinal bacteria that may

be replaced with different but equally effective bugs.

" We don't all have the same bacteria although they all seem to have been

organized to do the same things, " Birren said. It may be that our lifestyle and

environment " induces each of us to have arrived at a solution that works for

us. "

With this first snapshot of what normal looks like, studies now are under way to

see how the microbes differ in people with certain diseases, in hopes of

learning how to prevent or treat the illnesses.

Consider the intestinal superbug named C. difficile that people all too often

catch while they're in the hospital, and that sometimes kills. Washington

University's Tarr wants to know what mixture of gut bacteria can fend off the

diarrhea-causing germ or make it more likely to infect - so that doctors might

one day know who's more vulnerable before they enter a hospital.

Also, researchers at Baylor College of Medicine reported Wednesday that the kind

of bacteria living in the vagina changes during pregnancy, perhaps to give the

fetus as healthy a passage as possible. Previous research has found differences

in what first bacteria babies absorb depending on whether they're born vaginally

or by C-section, a possible explanation for why cesareans raise the risk for

certain infections.

All new information in some ways is humbling, because it shows how much more

work is needed to understand this world within us, noted infectious disease

specialist Dr. Relman of Stanford University, who wrote a review of the

project's findings for the journal Nature.

For example, the project included mostly white volunteers who live around

Houston and St. Louis. Relman said more work is needed to define a normal

microbiome in people with different racial, ethnic and geographic backgrounds.

And there are many remaining questions about how these microbes interact with

human genetics.

" We are essentially blind to many of the services that our microbial ecosystems

provide - and on which our health depends, " Relman wrote.

___

Online:

Nature: http://www.nature.com

PLoS: http://www.ploscollections.org/hmp

S. Kalman PhD, RD, FACN

Director, BD - Nutrition & Applied Clinical Trials

Miami Research Associates

6141 Sunset Drive - Suite 301

Miami, FL. 33143

Direct -

Office ext. 5109

Fax

Email: dkalman@...

Web: www.miamiresearch.com<www.mraclinicalresearch.com/>

Linked In: http://www.linkedin.com/in/douglaskalmanphdrd