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See Inside October 2006

Digestive Decoys

Bacteria take toxic bullets aimed at human cells

Travelers to the tropics usually try to avoid consuming the local microscopic flora responsible for "Montezuma's revenge" and other, more life-threatening intestinal illnesses. But an Australian research team thinks the best way to protect against those harmful gut bacteria may be to swig more bacteria: specifically, a benign strain of Escherichia coli genetically engineered to absorb other bacteria's toxins.

James C. Paton and his colleagues at the University of Adelaide altered a harmless strain of E. coli so that it sports human-like docking sites on the surface of its cell membrane. The idea is for bacterial toxins to bind to the decoy cells instead of to cells lining the human gut. The group's latest version mimics the human cell receptors for cholera toxin, and each bug soaks up 5 percent of its own weight in poison. In a test tube, the decoy bacteria neutralize 99.95 percent of the toxin's ability to kill human cells. When a dozen baby mice were given the modified bacteria and then infected with Vibrio cholerae, eight survived, whereas all 12 cholera-infected control mice died. Two thirds of the test mice survived even when researchers waited four hours after infection to treat them.

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