The US Department of Health and Human Services (HHS) has announced last week that the Department of Defense Multidrug-resistant Organism Repository and Surveillance Network (MRSN) at the Walter Reed Institute of Research had identified the first colistin-resistant mcr-1 E. coli in a person in the United States. The discovery is of concern because colistin is used as a last-resort drug to treat patients with multi-drug resistant infections. Finding colistin-resistant bacteria in the United States is important, as it was only last November that scientists in China first reported that the mcr-1 gene in bacteria confers colistin resistance. The mcr-1 gene exists on a plasmid, a small piece of DNA that is not a part of a bacterium’s chromosome. Plasmids are capable of moving from one bacterium to another, spreading antibiotic resistance between bacterial species.
The colistin-resistant E. coli was discovered in the urine sample of a female patient with no recent travel outside of the US. 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.
HHS’s Centers for Disease Control and Prevention is working with DoD, the Pennsylvania Department of Health, local health departments, and others to identify 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. The National Antimicrobial Resistance Monitoring System (NARMS) is also continuing to search for evidence of colistin-resistant bacteria in the United States.
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 in near real-time.
The two detections of the mcr-1 gene in the U.S. provide a new clue into the antibiotic resistance landscape, and it also highlights how much is not understand. Colistin is rarely used in human medicine compared to other antibiotics. It is often used to treat multi-drug resistant infections and its use is increasing. It is not used in animals in this country. As such, the new detection underscores the urgent need for more research in this area