(NaturalNews) A group of Canadian and French scientists have uncovered more evidence that prolific use of antibiotics in animal agriculture is contributing to the development of drug-resistant "superbugs," in a study published in Journal of Environmental Quality and funded by Agriculture and Agri-Food Canada.
Feeding antibiotics to healthy animals is a common practice in industrial agriculture, because it is believed to reduce rates of illness and to result in larger animals and therefore, higher profits. But many health advocates have raised concerns that this practice may accelerate the evolution of antibiotic-resistant bacteria. These bacteria might evolve directly in the animals' bodies, becoming superbugs if they somehow spread to humans (as in E. coli contamination from cattle feces). In addition, large quantities of unmetabolized antibiotics are secreted in farm animals' manure, which is then used as fertilizer all across North America - creating the potential for the evolution of drug resistance in the wider environment.
In the new study, researchers found a new, previously unknown type of drug resistance that combined two already well known bacterial abilities.
It is well established that bacteria readily evolve two major forms of drug-resistance: either they develop ways to purge drugs from their cells, or they metabolize the drugs to make them less harmful. Likewise, it is well known that some bacterial species can actually consume certain pesticides for food - to such an extent that those chemicals become ineffective in fields where such bacteria reside.
Now, researchers have found a species of bacteria that eats antibiotics for food.
"I think it's kind of a game changer in terms of how we think about our environment and antibiotic resistance," Topp said.
Producing new superbugs
14 years ago, Topp and colleagues began a long-term study in which they gave soils an annual treatment with three different veterinary antibiotics: sulfamethazine, tylosin, and chlortetracycline. They wanted to find out whether over time, this would encourage the evolution of antibiotic resistance in soil bacteria.
A few years ago, the researchers decided to start another concurrent study comparing the rate at which antibiotics broke down in soil that had received repeated doses versus soil that had never been dosed before. This was based on prior findings that many pesticides break down more quickly in soil where they have been regularly applied. The researchers wanted to find out if there was any selection for antibiotic-degrading microbes, which had never before been observed.
To their shock, they found that sulfamethazine broke down five times faster in soil that had been regularly exposed to it. They eventually determined that a strain of Microbacterium - from a family called actinomycete that are known to break down many organic compounds - was actually using sulfamethazine as food. Since then, two other strains of Microbacterium have been found to break down antibiotics in the sulfanomide family.
This implies that continued use of agricultural antibiotics may be exerting a pressure on soil bacteria to evolve antibiotic-digesting abilities, Topp noted. This is an issue of particular concern because unrelated bacterial species are able to swap genetic material.