First discovery of colistin resistance in a human E. coli infection.

February 14, 2017

Colistin is an antibiotic, also known as polymyxin E, produced by certain strains of the bacteria Paenibacillus polymyxa. It remains one of the last-resort antibiotics to treat multidrug resistant bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter. Colistin is considered the last agent used to fight “super bugs”, i.e. bacteria resistant to the strongest antibiotics including carbapenem-resistant Enterobacteriaceae (CRE), because bacteria were not exchanging genes for its resistance.

A latest discovery shows that bacteria may be exchanging resistance for colistin and that this antibiotic may not be effective anymore in antimicrobial treatments.

The Multidrug Resistant Organism Repository and Surveillance Network (MRSN) at the Walter Reed Army Institute of Research (WRAIR) characterized a transferrable gene of colistin resistance in the US, called mcr-1 gene. The mcr-1 gene exists on a plasmid, genetic element independent of the host genome that is capable of jumping from one bacterium to another, spreading antibiotic resistance between bacterial species.

In November 2015, public health officials worldwide reacted with alarm when this first transferrable gene for colistin-resistance was identified in China. Indeed, Chinese and British researchers found the colistin-resistant strain in pigs and raw pork and in a small number of people in China. Since the report, the global health community has been hunting for this gene that was later reported in Europe and in Canada and, as of now, in the US.

E. coli bacteria carrying the mcr-1 gene were found in a urine sample from a woman patient, with no recent travel outside of the US, in a military treatment facility in Pennsylvania. Fortunately the woman did not have CRE and the bacteria identified are not resistant to all antibiotics. However, the presence of mcr-1 gene and its ability to transfer its colistin resistance to other bacteria such as CRE raise the risk of emergence of truly pan-drug resistant bacteria.

An urgent public health response is underway to contain and prevent potential spread of mcr-1 gene. The investigation is focused on identifying reservoirs of this gene within the military healthcare community and preventing its spread. Active surveillance of multidrug resistant organisms, such as mcr-1 carriers, allows for earlier and more accurate identification of originating sources.

Recognized as a model program by the White House, the MRSN is a key component of the National Action Plan for Combating Antibiotic Resistant Bacteria (CARB). Together with the CARB, the Centers for Disease Control and Prevention and other government agencies will continue to put efforts to fight this global health crisis and track, slow and respond to the emergence of antibiotic resistance.

Journal reference:

Patrick McGann, Erik Snesrud, Rosslyn Maybank, Brendan Corey, Ana C. Ong, Robert Clifford, Mary Hinkle, Timothy Whitman, Emil Lesho and Kurt E. Schaecher. Escherichia coli Harboring mcr-1 and blaCTX-M on a Novel IncF Plasmid: First report of mcr-1 in the USA. Antimicrobial Agents and Chemotherapy, 2016.