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Along with their usual rations of grain and prepared feed, factory-farmed hogs and chickens in the United States dine on a steady diet of antibiotics. The animals are given the drugs not to prevent or cure illness but simply because low-level doses stimulate them to grow faster than untreated animals. This may be good for agribusiness's bottom lines, but an increasing body of research shows that it might be very bad for public health.
Several scientific examinations of pork and poultry operations in this country have shown that anti-microbial-resistant "superbugs," such as flesh-eating methicillin-resistant Staphylococcus Aureus (MRSA) and certain tough-to-kill strains of E. coli, are showing up not only in farm animals but also in the humans who tend them—and even in members of their families who don't work on the farms.
Now, a group of researchers at Boston University has discovered a mechanism that causes these superbugs to develop. It could mean that the problem is even worse than previously imagined. Their results are reported in the current issue of the journal Molecular Cell.
In earlier studies, the scientists had found that drugs that kill bacteria do so in part by stimulating the production of free radicals in those bacteria—not unlike the ones in humans that contribute to heart disease, cancer, and other maladies. However, when antibiotics are administered to the bacteria at low levels, as they are on factory farms, instead of killing the bugs the free radicals cause genetic mutations—far more than would normally occur. Some of those mutations lead to new strains of bacteria that can survive what were once lethal doses of drugs.