Researchers find rare superbug gene at U.S. pig farm

December 07, 2016

Researchers have found a rare and frightening superbug gene on a U.S. pig farm and are not sure how it got there. The superbug, clinically known as carbapenem-resistant enterobacteriaceae (CRE), was found after researchers swabbed the floors and walls of the farm’s pens and collected fecal samples during a five-month period in 2015.

According to study published in the journal Antimicrobial Agents and Chemotherapy, no pigs scheduled for slaughter carried the mutant gene and researchers haven't found any threat to humans yet. The gene, called bla IMP-27, gives bacteria the ability to resist the effects of a class of antibiotics called carbapenems, which are considered a last-resort treatment for hard-to-fight bacterial infections.

"It is an extremely rare gene. How it got on this farm, we don't know," said Thomas Wittum, chair of the veterinary medicine team at The Ohio State University, who led the study. “We found no evidence that these organisms were entering the food supply, but that is the concern: that it could happen on this or other farms.”

According to the study, the superbug gene is carried on an easily swapped bit of genetic material called a plasmid, and the researchers found it in several different species of bacteria on the farm. Carbapenem antibiotics are banned on farms, and in veterinary use, to avoid the risk of drug-resistant bacteria being transferred to humans, adding to the mystery of how the bacteria got there in the first place.

The amount of antibiotics that farms administer to their livestock has increasingly become a concern to some, and according to the Centers for Disease Control and Prevention, over 9,000 infections a year are caused by CRE bacteria, and at least 600 of those end in death.

Just this past summer, researchers sounded the alarm about a drug-resistant E. coli sample carrying a gene called mcr-1. It was also carried on a plasmid, and the fear is that an E. coli bacteria with the mcr-1 gene could pass it to another superbug with other mutations — creating a truly super superbug that resists all known antibiotics.

Something similar could potentially happen with the bla IMP-27 gene found at the pig farm, the researchers explained.

Wittum and his team had been checking samples submitted to testing labs from pigs suspected of carrying bad infections, and from a few samples sent from farms. The bla IMP-27 gene turned up in a single farm sample, Wittum said in an article.

"The implication of our finding is that there is a real risk that CRE may disseminate in food animal populations and eventually contaminate fresh retail meat products," the researchers wrote. Even if it doesn't make people sick right away, it could colonize people who handle the raw meat. Colonization means people (or animals) carry a germ but don't get sick from it — but if they do become ill with something else, the bacteria can multiply. Plus, colonized people can infect sick or frail people.

Wittum also said that the pigs from the farm where the superbug gene was found were never given any carbapenem drugs and they were not dosed with antibiotics to promote their growth — a common but increasingly condemned practice known to contribute to the rise of antibiotic resistance.

"We may need to examine some of the practices of farms, and evaluate whether they are really appropriate, and whether the benefits outweigh the risks," Wittum added.

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Category: Food Safety