OCTOBER 2, 2008
The Body as Bacterial Landlord
Trillions of Microbes Living in and on Us Cause Some Harm but Also Afford Protection
By ROBERT LEE HOTZ
ists discovered that bacteria, not stress, caused most stomach ulcers, the insight overturned a century of medical dogma, transformed clinical practice and garnered a 2005 Nobel Prize for the two researchers who made the connection so many others had missed. After people adopted antibiotics to treat gastric distress, though, microbiologist Martin Blaser and his colleagues at New York University began to document an odd medical trend. Ulcers did drop dramatically, as expected. So did the incidence of stomach cancer. As the bacteria, called Helicobacter pylori, virtually disappeared among children, however, cases of asthma tripled. So did rates of hay fever and allergies, such as eczema. Among adults, gastric reflux disease became more common, as did some forms of esophageal cancer, researchers noted. To Dr. Blaser's way of thinking, antibiotics and other sanitation measures are eliminating the harm these bacteria cause at the expense of the protection they provide us.
The human body teems with so many microbes that they outnumber our own cells ten to one. Vast schools of bacteria are in us and around us, like fish nuzzling a coral reef. "They are not simply along for the ride," says Stanford University microbiologist David Relman. "They are interacting with us." Yet almost all of them are still unknown to science, since most cannot be grown and studied in the laboratory. In ways mysterious to medicine, this microbial menagerie of fellow travelers in and on us is controlling our health, affecting obesity, cancer and heart disease, among others.
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As many as 500 species of bacteria may inhabit our guts, like H.pylori. Maybe 500 or so other species make themselves at home in our mouth, where each tooth has its own unique bacterial colony, Dr. Relman recently determined. No one knows how many species we contain in all. This past August, researchers at Kings College London identified yet another new species of oral bacteria between the tongue and cheek. Until recently, half of humanity harbored these H. pylori stomach bacteria, according to a 2002 study in the New England Journal of Medicine. Indeed, we appear to have evolved together. Among those born in the U.S. during the 1990s, however, only 5% or so still carry these microbes, largely due to the indiscriminate use of antibiotics. After analyzing health records of 7,412 people collected by the National Center for Health Statistics, Dr. Blaser and NYU epidemiologist Yu Chen reported this summer in the Journal of Infectious Diseases that children between three and 13 years old who tested positive for H. pylori bacteria were 59% less likely to have asthma. They also were 40% to 60% less likely to have hay fever or rashes. No one knows yet whether Dr. Blaser is right about H. pylori's protective properties.
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The connection to allergies is just one of the pressing public health puzzles posed by our complex relationship with the trillions of microbes that call us home. "Recent studies have shown that changes in bacteria can be correlated with some pretty serious diseases," says Jane Peterson, head of the National Human Genome Research Institute's comparative sequencing program. Childhood diabetes also is on the rise in developed countries, for instance. Last week, University of Chicago immunologist Alexander Chervonsky and his collaborators at Yale University reported that doses of the right stomach bacteria can stop the development of Type 1 diabetes in lab mice.
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Helicobacter pylori accompanied our ancestors on every journey. The human varietals spread from East Africa about 58,000 years ago as anatomically modern humans also first began to migrate from the region, molecular epidemiologists at the Max Planck Institute for Infection Biology in Berlin reported last year in the journal Nature. They identified 370 strains of the bacteria that seemed to reflect the migrations and settlements of their human hosts. Most of us learn early to think of all micro-organisms as harmful germs. The thought of our intimate zoo, therefore, may make some of us reach reflexively for the antiseptic. In the U.S. alone, antibacterial products account for about $1 billion in sales annually. It is unclear, though, how long we could survive without each other.
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