By Jerry Adler and Jeneen Interlandi
NEWSWEEK Oct 29, 2007 Issue
Behold yourself, for a moment, as an organism. A trillion cells stuck together, arrayed into tissues and organs and harnessed by your DNA to the elemental goals of survival and propagation. But is that all? An electron microscope would reveal that you are teeming with other life-forms. Any part of your body that comes into contact with the outside world—your skin, mouth, nose and (especially) digestive tract—is home to bacteria, fungi and protozoa that outnumber the cells you call your own by 10, or perhaps a hundred, to one.
Their ancestors began colonizing you the moment you came into the world. There are thousands of different species, found in combinations "as unique as our DNA or our fingerprints," says Stanford biologist David Relman, who is investigating the complex web of interactions microbes maintain with our digestive, immune and nervous systems. Where do you leave off, and they begin? Microbes, Relman holds, are "a part of who we are."
As antibiotics lose their effectiveness, researchers are returning to an idea that dates back to Pasteur, that the body's natural microbial flora aren't just an incidental fact of our biology, but crucial components of our health, intimate companions on an evolutionary journey that began millions of years ago. The science writer Jessica Snyder Sachs summarizes this view in four words in the title of her ground-breaking new book: "Good Germs, Bad Germs." Our microbes do us the favor of synthesizing vitamins right in our guts; they regulate our immune systems and even our serotonin levels: germs, it seems, can make us happy. They influence how we digest our food, how much we eat and even what we crave. The genetic factors in weight control might reside partly in their genes, not ours. Regrettably, it turns out that bacteria exhibit a strong preference for making us fat.
Some bacteria seem to be both good and bad. The best-known is Helicobacter pylori, a microbe that has evolved to live in the acid environment of the stomach. It survives by burrowing into the stomach's mucous lining and secreting enzymes that reduce acidity. Nobel laureates Barry Marshall and Robin Warren showed it could cause gastric ulcers and stomach cancer. But then further studies discovered that infection with H. pylori was protective against esophageal reflux and cancer of the esophagus, and may also reduce the incidence of asthma. H. pylori, which is spread in drinking water and direct contact among family members, was virtually universal a few generations ago but is now on the verge of extinction in the developed world. The result is fewer ulcers and stomach cancer, but more cancer of the esophagus—which is increasing faster than any other form of cancer in America—more asthma, and … what else? We don't know. "H. pylori has colonized our guts since before humans migrated out of Africa," says Blaser. "You can't get rid of it and not expect consequences."
And there's one more thing that microbes can do, perhaps the most remarkable of all. Mycobacterium vaccae, a soil microbe found in East Africa that has powerful effects on the immune system, was tested at the University of Bristol as a cancer therapy. The results were equivocal, but researchers made the startling observation that patients receiving it felt better regardless of whether their cancer was actually improving. Neuroscientist Chris Lowry injected mice with it, and found, to his amazement, that it activated the serotonin receptors in the prefrontal cortex—in other words, it worked like an antidepressant, only without the side effects of insomnia and anxiety. Researchers believe M. vaccae works through the interleukin-10 pathway, although the precise mechanism is uncertain. But there is at least the tantalizing, if disconcerting, suggestion that microbes may be able to manipulate our happiness. Could the hygiene hypothesis help explain the rise in, of all things, depression? We're a long way from being able to say that, much less use that insight to treat people. But at least we are asking the right questions: not how to kill bacteria, but how to live with them.
(Excerpt from: Caution: Killing Germs May Be Hazardous to Your Health)
Complete story at: http://www.newsweek.com/id/57368?GT1=10450
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