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Monday, December 17, 2012

Antibiotic resistant soil

You know that not taking all your antibiotics can lead to the evolution of drug resistant bacteria. You even know that a much larger problem is the amount of antibiotics given to livestock. But what you may not have realized is that the problem isn’t just that the bugs living in animals will become drug resistant and then infect humans. No, a bigger problem may be that bacteria living in soil can become resistant to drugs pooped out of medicated animals. Yes, antibiotic resistance is being spread throughout our agricultural fields.

Researchers from Agriculture and Agri-Food Canada applied a mix of sulfamethazine (SMZ), tylosin (TYL), and chlortetracycline (CTC), three kinds of antibiotics common in livestock management, to fields annually for ten years. At the end of that time, soil samples were taken and compared to similar fields that had not been treated. 

When the scientists added SMZ or TYL to the samples, they found that the drugs biodegraded much more quickly from fields that had previously been exposed to those drugs. In other words, the bacteria in the virgin soils were far less equipped to deal with the influx of antibiotics. In contrast, bacteria that had spent the last ten years in soil containing antibiotics had adapted to those drugs. The scientists even discovered at least one type of bacteria that was not only resistant but appeared to actually use SMZ as a nutrient source.

This news isn’t necessarily bad. As long as the soil bacteria don’t affect human health (and I realize that’s a big if), we might be able to employ them to clean up fields before the drugs deposited there by livestock can leach into water sources. Of course, we have little hope of cataloguing, let alone managing, all the kinds of bacteria living in the dirt. So we’re all probably better off if fewer drugs get deposited in those fields going forward.

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Edward Topp, Ralph Chapman, Marion Devers-Lamrani, Alain Hartmann, Romain Marti, Fabrice Martin-Laurent, Lyne Sabourin, Andrew Scott, & Mark Sumarah (2012). Accelerated Biodegradation of Veterinary Antibiotics in Agricultural Soil following Long-Term Exposure, and Isolation of a Sulfamethazine-degrading Microbacterium Journal of Environmental Quality : doi: 10.2134/jeq2012.0162.