Antibiotic resistance may increase outside of organisms

Doug Call

Researchers from Washington State University recently discovered a new means for the spread of antibiotic resistance.

The unlikely recipe is a mix of cow dung and soil, with urine containing a metabolized antibiotic added. The urine will kill normal E. coli within the dung and soil, but anti-biotic resistant E. coli will survive.

The resistant bacteria in the dung and soil mixture can then recolonize inside new cattle as they pasture, forage or bed near the bacteria.

“I was surprised at how well this works, but it was not a surprise that it could be happening,” Doug Call, a molecular epidemiologist at the WSU Paul Allen School for Global Animal Health, said.

Call made the discovery as leader of a research team that included immunology and infectious disease Ph.D. student Murugan Subbiah. There study on E. coli and antibiotic resistance appears in a recent issue of the online journal PlOS ONE.

Antibiotics were once considered a miracle of modern science and have been successful at dramatically reducing infections worldwide over the past 70 years. Their widespread and often indiscriminant use, however, has led to the development of resistant microbes. Animals have become a significant source of drug-resistance because they receive the majority of the antibiotics sold in the United States.

Until now, most scientists believed that resistance developed inside an animal’s stomach. Call’s study showed how some antibiotics have little effect on bacteria inside an animal’s gut.

“Given that about 70 percent of the drug is excreted in the urine, this was about the only pathway through which it could exert such a large effect on bacterial populations that can reside in both the gut and the environment,” Call said. “If our work turns out to be broadly applicable, it means that selection for resistance to important drugs like ceftiofur occurs mostly outside of the animals. This in turn means that it may be possible to develop engineered solutions to interrupt this process. In doing so we would limit the likelihood that antibiotic resistant bacteria will get back to the animals and thereby have a new approach to preserve the utility of these important drugs.”

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