Tracking mcr -1

In November 2015, mcr -1—a gene that can make bacteria resistant to colistin, an old antibiotic that is the last-resort drug for some multidrug-resistant infections—was reported in China. The mcr -1 gene is on a plasmid, a small piece of DNA that is able to move from one bacterium to another. The gene has the potential to easily spread to other bacteria and raises the possibility that bacteria already resistant to major antibiotic drugs could become resistant to colistin as well.

With China’s report , CDC, U.S. Food and Drug Administration (FDA), and U.S. Department of Agriculture (USDA) began hunting for mcr -1 in the United States. The gene was first identified in the United States by the Department of Defense in bacteria cultured from a Pennsylvania patient and in a special study by the National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS) in intestinal samples of two pigs, one in South Carolina and the other in Illinois.

CDC released reports describing patients from Pennsylvania and Connecticut with bacteria containing the mcr-1 gene, and the public health investigation that followed.

The following map displays where the mcr -1 gene has been found in U.S. human and food animal sources as of September 7, 2016.