The Centers for Disease Control and Prevention (CDC) is tracking the mcr-1 gene in bacteria. This gene can make bacteria resistant to colistin, an antibiotic that is the “last resort” drug for some multidrug-resistant pathogens. Colistin is considered an old drug and is rarely used because it can damage the kidneys. The gene was found in China for the first time in November 2015.
The map shows where the mcr-1 gene has been reported in the United States as of January 1, 2017. In the states highlighted in yellow, human infections have been reported. The states highlighted in orange have animal infections.
The mcr-1 gene is on a plasmid, which is a piece of DNA that can move from one pathogen to another. Because of the ease of this transfer, bacteria that area already resistant to other major antibiotics could become resistant to colistin too.
The mcr-1 gene was first identified in humans in the United States by the Department of Defense in bacteria isolates from a patient in Pennsylvania. The National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS) cultured the gene from intestinal samples in two pigs.
The government launched an investigation of the human isolate in September 2016. The patient in question had no international travel for a year, no exposure to livestock, and a limited role in meal preparation. She had multiple and repeated admissions to four medical facilities in 2016.
A study was conducted to find out if transmission of the gene was occurring between patients. Seven patients at a high risk facility completed the screening process. No bacteria with the mcr-1 gene were detected in those patients. And no colistin-resistant organisms were detected among 51 violates collected from four facilities to which the patient was admitted in 2016. Government officials think that these findings indicate the risk for transmission from a colonized patient to otherwise healthy people might be relatively low.
Still, officials think that mcr-1 will be identified in this country with “increasing frequency.” In July 2016, mcr-1 in E. coli bacteria was found in a patient specimen in New York. And these findings highlight the urgency of a better approach to antibiotic stewardship.