STUDY: Long-Dreaded Antibiotic-Resistant Superbug Discovered on U.S. Pig Farms

WASHINGTON – Highly transmissible resistance to critical, last-resort antibiotics called carbapenems has been found in bacteria on farms in the U.S. for the first time, according to a new study released today in a journal of the American Society for Microbiology.

While this resistance has been found in humans in the U.S. before, its appearance on pig farms is troubling because livestock operations act as a kind of giant petri dish for resistance, helping it to spread more rapidly to humans and animals alike. And the routine administration of antibiotics to food animals that are not sick accelerates that process.

A statement follows from Dr. David Wallinga, MD, Senior Health Officer at the Natural Resources Defense Council:

“The last terrible shoe may have just dropped when it comes to drug-resistant infections. This is just one more warning that doctors may soon have nothing left in their toolkit to save patients when these bugs strike. Our overuse of antibiotics in livestock is creating reservoirs for the spread of resistance – and this study strongly suggests resistance to carbapenems is no exception. To save our miracle drugs, we have got to stop wasting them on animals that aren’t sick.”


Already, carbapenem-resistant bacteria (CRE) cause about 9,300 infections, and 600 deaths in U.S. hospitals annually. CRE are among the Centers for Disease Controls’ top three “urgent threats” from antibiotic resistance. CDC Director Tom Frieden has called them “nightmare bacteria.”

When strains of certain common bacteria (like E coli or Klebsiellae) become resistant to more common, less toxic antibiotics, carbapenems have been critical last-resort drugs doctors could turn to and have some hope that they would work.

To date, most CRE infections have occurred in hospitals, nursing homes, and other healthcare settings. More of these potentially fatal infections are expected to pop up in communities, as carbanem resistance that is carried on easily shared pieces of DNA, called plasmids, spreads among different kinds of bacteria. This study is the first to find CRE bacteria carrying these plasmids on pig farms. The same kind of resistant bacteria has also been recently been found in human patients in Great Plains states.

Resistance to another drug of last resort, called colistin, was found on U.S. pig farms for the first time earlier this year. This resistance gene also was carried on easily transmitted plasmids. If resistance genes to both of these last-resort drugs are found on the same plasmid acquired by disease-causing bacteria, it will create virtually unbeatable superbugs. This study suggests that farm antibiotic use is a factor in making that a reality.


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