Antibiotic-Free Pigs Remain Home for Resistant Bacteria

As more and more antibiotic-resistant pathogens appear in livestock, it seems logical that eliminating antibiotics from animal feed might reduce the levels of antibiotic-resistant bacteria. But that hasn’t proven true, according to Sid Thakur, PhD, assistant professor of population health and pathobiology at North Carolina State University College of Veterinary Medicine in Raleigh, whose latest research documenting the persistence of antibiotic-resistant strains of Campylobacter in antibiotic-free pigs was published Sept. 12, 2012, in the online journal PLOS One.

Dr. Thakur had previously found that antibiotic-resistant Campylobacter was present in both ABF-certified and conventionally raised pigs; in this, his most recent research, he and PhD student Macarena Quintana-Hayashi analyzed thousands of samples collected from pigs and their surrounding environments over the course of two years and found that the Campylobacter populations in both groups of pigs were genetically matched.

The antibiotic-free pigs had never come into direct contact with the pigs receiving antibiotics, so environment must play an enormous role in the persistence of antibiotic-resistant Campylobacter , Dr. Thakur concluded.

“We always tend to focus on the commodity—what bacteria is in the pig, or the chicken, or the cow?” he said. “But what’s around the animal? The environment probably has a lot of the answers about bacterial contamination, but it’s difficult to tackle. In most literature, you’ll see that the researchers sampled the birds or the pigs but not the environment as well.”

Dr. Thakur and his student exhaustively sampled the environment on the pigs’ farms—soil, drinking water, feed, surfaces. “On pretty much everything the pigs come in contact with, we found the same resistant bugs. Where are those coming from? That’s very difficult to answer,” he said. “Studies have recently been published about antibiotic-resistant bacteria being found in soil. How do you get rid of soil bacteria? I don’t know the answer, but our findings make it pretty clear that we’re not going to solve the problem of drug-resistant bacteria by taking animals off antibiotics.”