Government scientists found the MCR-1 gene, which allows bacteria to overcome the last-resort antibiotics used against disease in humans, in a sample taken from a different pig than the first U.S. discovery, said a CDC official. The initial case, reported on the same day as discovery of a Pennsylvania woman with an infection that carried the MCR-1 gene, raised fears of “superbug” bacteria resistant to a broad array of antimicrobials.
Beth Bell, director of the CDC’s National Center for Emerging and Zoonotic Diseases, told a House Energy and Commerce subcommittee that USDA scientists found the second case as part of the inter-agency monitoring program that also found the first sample of MCR-1 in a sample of pig intestines. “An isolate from a second pig is undergoing analysis,” said Bell.
The MCR-1 gene is carried by a plasmid, a small piece of DNA that can move among bacteria, spreading resistance to antibiotics among species of bacteria. In the first pig sample that contained MCR-1, the USDA determined that bacteria resistant to colistin, the last-resort antibiotic, also resisted four other antibiotics. “The resistance to these other antibiotics was not on the plasmid carrying the MCR-1 gene,” said Bell.
The Washington Post said the newest sample of MCR-1 and colistin-resistant bacteria was detected on May 27, three months after the first discovery. “USDA officials have provided few details, including where either animal was raised or killed,” said the Post.
MCR-1 was first identified in China in 2015 among animals and humans. The U.S. detections in May involved different types of the E coli bacteria.
“The latest animal case suggests the [MCR-1] gene is already circulating through multiple routes here,” said the Post.
To read written testimony from Bell and other witnesses at the hearing, click here.