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Investigating Antibiotic-Resistant Pathogens in Swine Herds

Sid Thakur is an expert on the kinds of pathogens that like to make their homes in and around our pig populations. He spends most of his time testing the pigs and their environment, identifying potential dangers such as Campylobacter – a nasty little critter that we definitely don’t want in our food supply, particularly in an antibiotic-resistant form.

The rise of antibiotic-resistant pathogens like Campylobacter is a concern for the food animal industry. Some pig farms have switched to raising antibiotic-free, or ABF pigs, in an attempt to get away from the conditions that facilitated antibiotic resistance in the first place. The reasoning goes like this: pathogens expend energy to maintain and retain genes that give them antibiotic resistance. So if we removed the pressure; i.e., the antibiotics, from the environment, then the pathogens could eventually shed the extra genes and voila! Problem solved.

That’s where Dr. Thakur comes in. He’s been taking samples from both conventionally raised pigs and pigs that are ABF-certified for about 10 years now, to see if there has been any decrease in drug resistance among important bacterial food-borne pathogens like Salmonella and Campylobacter.

In his latest study, Dr. Thakur and his Ph.D. student Macarena Quintana-Hayashi looked at Campylobacter. He tested pigs from ABF and conventional farms, and took environmental samples from soil, barns, etc. Each pig was tested five times at different stages during its life cycle and in different facilities, because the pigs can come into contact with pathogens at any point during their lives.

They found that both the ABF and the conventionally raised pigs tested positive for antibiotic-resistant strains of pigs Campylobacter, although the rates of resistance were higher for conventionally raised pigs. Against tetracycline, one of the most commonly used antimicrobial drugs, 48.2 percent of the ABF farm samples taken were resistant, while 88.3 percent of the conventional farm samples were resistant. They even found resistance against ciprofloxacin – a very powerful antimicrobial – in both sets of pigs, although thankfully at much lower rates. Dr. Thakur and Quintana-Hayashi also found that the surrounding environment plays a very important role in the transmission of the pathogen to the pigs at both farm and slaughter.

So what does this mean? In terms of food safety, not much. Cleaning and chilling processes ensure that by the time the pork from these pigs arrives at your grocery store, almost all pathogens are gone.  Proper cooking takes care of any remaining bugs. And Campylobacter doesn’t affect the health of the pigs on the farms.

In terms of antibiotic resistance, Dr. Thakur thinks there are a number of factors still at work. “Drug-resistant Campylobacter has been around for a while,” he says. “This form of the pathogen has been shown to be better fit to survive compared to the drug-sensitive form. This means that when Campylobacter establishes itself in a particular environment it takes steps to make sure no other pathogens can move into its territory. It is also a pathogen that does well in the environment itself, not just in a host animal like a pig.

“We’re still in the early stages in terms of seeing whether we can reverse drug resistance in pathogens like Campylobacter. It may just be a matter of time.”

--Tracey Peake

For more information:

Thakur Molecular Epidemiology Laboratory

Dr. Thakur Receives Sigma Xi Research Award

CVM Studies Feral Pig Population for Evidence of Salmonella

Posted June 14, 2012