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We Need Some Bad Bugs

Posted By Prucia Buscell, Thursday, June 7, 2012

Scientists suspect that alterations in the human microbiome, caused by changes in modern life styles and medicines, have be contributing to an increase in obesity and autoimmune disorders.

"The Ultimate Social Network," a story by Jennifer Ackerman in the June 2012 issue of Scientific American, describes research into the functioning of the complex ecosystem of bacteria and other microorganisms that inhabit our bodies. Biologist Sarkis Mazmanian at the California Institute of Technology has studied the intestinal organism bactericides fragilis and its role in the human immune system. It is pathogenic and can cause trouble, but as part of a community of commensals-the trillions of microbial cells and the genes they contain that make up our microbiome, b. fragilis help regulate the immune system. Read an article by Mazmanian and others here. B. fragilis seems to help produce a balance between the activities of T cells that provoke inflammation and T cells that counteract inflammation.

Over the last century, life style changes have decreased the incidence of b. fragilis and other regulatory bacteria in the gut, and Mazmanian thinks that maybe be one cause of an increase in autoimmune disorders as Crohn's disease, Type I diabetes, and multiple sclerosis.

Martin Blaser, a professor of internal medicine and microbiology at New York University, has studied the role of Helicobactor pylori, which got a bad reputation some years ago for being the cause of peptic ulcers. Three decades ago, more than 80 percent of Americans were host to H. pylori, but now fewer than six percent of American children test positive for it. It turns out that H. pylori helps regulate two hormones that impact appetite-ghrelin, which tells the brain we're hungry, and leptin, which signals that we're full. The Scientific American story reports on a study that showed 92 veterans treated with antibiotics to eliminate H. pylori gained more weight than their uninfected peers who still had the bacteria. Blaser speculates that widespread use of antibiotics to treat childhood ear infections has caused alterations in their intestinal microbiomes that may help explain the rise in childhood obesity. A New York Times story on the good that bad bugs can do reports Blaser's belief that antibiotics are causing complex and alarming changes in our microbiomes.

Mazmanian too worries about the loss of poorly understood bacteria through antibiotic use and other life style changes and our tendency to think of all bacteria as pathogenic. "What we've done as a society over a short period is completely change our association with the microbial world," he told the Scientific American. He believes autoimmune diseases have both genetic and environmental components, and he thinks the environmental component is microbiotic and the changes that are effecting our immune systems.

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