Discovery of first mcr-1 gene in E. coli bacteria found in a human in United States

MCR-1 causes resistance to colistin, a last-resort drug for treating resistant infections

Media Statement

For Immediate Release: Tuesday, May 31, 2016
Contact: Media Relations,
(404) 639-3286

The Centers for Disease Control and Prevention is part of a coordinated public health response after the Department of Defense (DoD) announced the discovery of the first mcr-1 gene found in bacteria in a human in the United States. CDC is working with DoD, the Pennsylvania Department of Health, local health departments, and others to identify people who have had contact with the patient and take action to prevent local spread.

E. coli bacteria carrying the MCR-1 gene was found in a urine sample from a Pennsylvania woman with no recent travel outside of the U.S. The mcr-1 gene makes bacteria resistant to the antibiotic colistin, which is used as a last-resort drug to treat patients with multi-drug-resistant infections, including carbapenem-resistant Enterobacteriaceae (CRE).  The mcr-1 gene exists on a plasmid, a small piece of DNA that is capable of moving from one bacterium to another, spreading antibiotic resistance among bacterial species.  The CDC and federal partners have been hunting for this gene in the U.S. ever since its emergence in China in 2015.

Despite some media reports, the Pennsylvania State Health Department investigation has determined that the woman did not have CRE and the bacteria identified is not resistant to all antibiotics (referred to as a pan-resistant infection). The presence of the mcr-1 gene, however, and its ability to share its colistin resistance with other bacteria such as CRE raise the risk that pan-resistant bacteria could develop.

The investigation is currently focused on identifying close contacts, including household and healthcare contacts, of the Pennsylvania patient to determine whether any of them may have been at risk for transmission of the bacteria containing the mcr-1 gene.

Beginning in fall 2016, CDC’s Antibiotic Resistance Lab Network will provide the infrastructure and lab capacity for seven to eight regional labs, and labs in all states and seven major cities/territories, to detect and respond to resistant organisms recovered from human samples . State labs will be able to detect new forms of antibiotic resistance—including mutations that allow bacteria to survive the effects of the last-resort drugs like colistin—and report these findings to CDC.  With this comprehensive lab capacity, state health labs and regional labs that are part of the network will be able to investigate emerging resistance faster and more effectively, generating better data for stronger infection control among patients to prevent and combat future resistance threats. CDC will also provide new resources to state health departments to support their efforts to stop antibiotic-resistant outbreaks and prevent the spread of antibiotic-resistant pathogens across communities.

Consistent with the National Action Plan for Combating Antibiotic-Resistant Bacteria, CDC and other government agencies will continue efforts to track, slow and respond to the emergence of antibiotic resistance.

For more information on the mcr-1 discovery, see


Page last reviewed: May 31, 2016