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Emerging diseases : The killer within

点击量:   时间:2017-11-20 04:01:12

By Nell Boyce Atlanta WASHING salad vegetables doesn’t guarantee protection against foodborne pathogens, say Japanese researchers. They have found that Escherichia coli O157 can find its way inside plant tissue. Radish sprouts used as salad toppings are thought to have caused the 1996 outbreak of E. coli O157 in Japan that killed 11 people and gave thousands more diarrhoea. So Masaaki Iwaki and his colleagues at the National Institute of Infectious Diseases in Tokyo have been investigating what happens to radish plants grown from contaminated seeds. The researchers soaked the seeds for eight hours in a solution spiked with the bacteria, and then placed the seeds in sterile water and allowed them to germinate and grow for seven days. When Iwaki and his colleagues cut cross sections of the plants, exposed them to a fluorescent antibody for E. coli O157 and examined them under the microscope, they saw telltale fluorescence. “In the tissue grown from contaminated seeds, you can see fluorescence just beneath the epidermis and also deeper inside the plant, which is not seen in control tissues,” says Iwaki. The researchers then took contaminated radish sprouts and dunked them in a powerful disinfectant, mercury chloride solution, for 10 minutes. When whole sprouts were put on a culture medium, no bacterial colonies grew. But if the disinfected sprouts were cut open, bacteria started to grow. To prevent infection, says Iwaki, it seems that people must either cook radish sprouts or ensure that seeds are uncontaminated. The findings are “very disturbing”, says Thomas Breuer of the Centers for Disease Control and Prevention in Atlanta, who has traced outbreaks of E. coli O157 to alfalfa sprouts. Irradiating seeds could provide some protection, he says,