Study finds identical strains of antibiotic-resistant C. coli in ABF and conventionally raised pigs

Researchers from North Carolina State University have found identical strains of antibiotic-resistant Campylobacter coli (C. coli) in both antibiotic-free (ABF) and conventionally raised pigs. This finding may indicate that these antibiotic-resistant pathogens can persist and thrive in the environment, regardless of antimicrobial usage by pork producers.

Dr. Siddhartha Thakur, assistant professor of population health and pathobiology, had previously found that antibiotic-resistant C. coli, a leading cause of foodborne illness in the U.S., was present in both ABF-certified and conventionally raised pigs. The pathogen was present in both groups in all facilities from breeding to processing. Thakur wanted to determine whether the C. coli that he found in each group was genetically the same, in order to see if the presence or absence of antimicrobial usage had an effect on the pathogen's genetic makeup.

The rise of antibiotic-resistant pathogens like C. coli is a concern for the food animal industry. Some pig farms have switched to raising ABF pigs in an attempt to get away from the conditions that facilitated antibiotic resistance in the first place. The hope is that once the selection pressure - in the form of antimicrobial use - on C. coli to retain antibiotic resistance decreases, the pathogen will lose its resistance.

Over several years, Thakur and Ph.D. student Macarena Quintana-Hayashi collected thousands of samples from pigs and their surrounding environments, and performed a genetic analysis on 200 representative isolates of C. coli, to see if these strains were similar. They found that the Campylobacter populations in the two swine production systems (conventional and ABF) were in fact the same. Since the different pig populations never came into contact, the researchers concluded that the environment must be playing a large role in the continuing survival of antibiotic-resistant C. coli.

Thakur's findings appear online in PLoS One.

"In the case of ABF pigs, the environment plays an important role in their exposure to these resistant strains," Thakur says. "If the environment itself, and not the pig, is serving as a reservoir for C. coli, then we will most probably continue to find resistant bacterial populations, regardless of a producer's antimicrobial use."