Friend turns to foe

By Andy Coghlan BACTERIA sprayed onto crops to kill pests can also harm people under certain circumstances. Microbiologists in France have treated a soldier who developed a serious wound infection caused by Bacillus thuringiensis. B. thuringiensis produces an insecticidal toxin, and so has become popular as a “natural” pesticide. Its role as a human pathogen emerged when a team at the military hospital in Saint-Mandé, near Paris, examined the wounds of a soldier injured in 1995 by a mine at Sarajevo airport in Bosnia. “He had a multiple fracture to the knee and severe shrapnel lesions,” says Eric Hernandez, one of the microbiologists. Initially the bacterium infecting the wounds was identified as Bacillus cereus, but unusual crystals in the cells prompted the team to have the strain rechecked. Laboratories at the WHO and at the Pasteur Institute in Paris independently identified the sample as B. thuringiensis serotype H34-konkukian. Hernandez and his colleagues put the same strain into wounds in mice with weakened immune systems. The bacteria caused a nasty infection—but only if they had first been grown in a medium containing blood. Exposure to blood seems to switch the bacteria into a pathogenic form. “We think they destroy the walls of blood cells,” says Hernandez. Farmers spray crops with the strains H1, H2 and H3, rather than the H34 serotype. But more recent work by the French team has shown that one of the commercial strains can also infect wounds in mice. Nevertheless, Jim Baum, research director at Ecogen of Langhorne, Pennsylvania, which markets B. thuringiensis, is confident that the sprays are safe. He says the bacteria are not exposed to blood, and so should not be primed to infect wounds. “There’s such a long history of safe use since the 1960s,” he adds. More on these topics:
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