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Microbial menace. A cocktail of gut bacteria may one day be used to treat the chronic diarrhea caused by this bacterium.

David Goulding Genome Research Limited

Using Gut Bacteria to Fight Diarrhea

A tonic of gut microbes may be the secret recipe for treating a common hospital scourge. Researchers have pinpointed the exact mix of microbes required to cure mice of a chronic infection by a hard-to-treat bacterium that causes bloating, pain, and diarrhea in people. A similar bacterial cocktail may one day be able to replace a controversial treatment involving the intake of fecal matter to restore the right balance of microbes in the gut.

Clostridium difficile is a menace in hospitals and nursing homes, causing nearly 336,000 infections and 14,000 deaths a year in the United States. Antibiotics can temporarily knock down the bacterium, but about 25% of infected people relapse, often multiple times, because the germ produces spores that hand sanitizers and hand washing don't kill. Antibiotics can also backfire because they kill the gut's normal microbial community, clearing the way for C. difficile to resettle.

In desperation, some physicians turned to an unpalatable resource: successfully treating patients by inserting a tube into their stomachs containing ground-up, filtered fecal material from a healthy person that contains a dose of beneficial microbes. But this treatment is controversial—and in some places, illegal—because of the risk of introducing other pathogens.

Searching for alternatives, microbiologist Trevor Lawley of the Wellcome Trust Sanger Institute in Hinxton, U.K., and his colleagues examined Clostridium infection in mice. Lawley and his colleagues first demonstrated that the germ's spores do lead to recurrences of the infection after antibiotic treatment and that fecal therapy cures the problem. They then cultured the fecal material used to cure the mice, isolating 18 types of bacteria. Finally, they began to mix and match, infecting mice with different combinations of the bacteria. Of the various combinations tried, only one, a mix of six very different kinds of bacteria, cured the mice, they report online today in PLoS Pathogens.

"It is an excellent, ground-breaking paper," says Brendan Wren, a microbiologist at the London School of Hygiene & Tropical Medicine who was not involved with the mouse study. He is now working with Trawley to determine if they can find an appropriate bacterial cocktail that will cure humans. If they succeed, Wren says, someday "a simple suppository of the bacteria could prevent C. difficile reinfection and obviate the need for antibiotics, which may exacerbate the problem."

*Correction, 5:20 p.m.: Some physicians have been successfully treating patients for C. difficile with ground-up, filtered fecal material inserted into the stomach with a tube, not via an enema.