Superbug resistant to last resort antibiotic identified in the US

By Sally Robertson, B.Sc.May 27 2016

Researchers have identified a transferrable gene for colistin resistance in the U.S. that may mean the “end of the road” for antibiotics.

Colistin is the last resort antibiotic for particularly dangerous superbugs that are resistant to the strongest antibiotics. Since bacteria had not been exchanging genes for colistin resistance, this antibiotic has been the best tool available for treating bacterial infections that are multidrug resistant.

This latest finding, however, shows that bacteria now seem to be exchanging these genes and colistin may be losing its effectiveness as an antibiotic.

Last November, microbiology researchers became alarmed when Chinese and British scientists reported that colistin-resistance was identified in pigs, raw pork meat and some individuals in China. Since then, global health experts have been searching for colistin resistant genes in humans and in the food supply.

Now, for the first time, a person in the U.S. has been found to have a bacterial infection resistant to colistin. The antibiotic-resistant strain was identified last month in the urine of a woman from Pennsylvania. The sample was sent to Walter Reed National Military Medical Center where it was tested for colistin susceptibility.

As reported in Antimicrobial Agents and Chemotherapy, the results showed that the infection could not be treated with any safe dose of colistin. The sample was then sent to the Multidrug Resistant Organism Repository and Surveillance Network (MRSN) at the Walter Reed Army Institute of Research (WRAIR) for sequencing, which revealed the presence of the colistin-resistant gene, mrc-1.

The emergence of a transferable gene that confers resistance to this vital antibiotic is extremely disturbing. The discovery of this gene in the U.S. is equally concerning, and continued surveillance to identify reservoirs of this gene within the military healthcare community and beyond is critical to prevent its spread.”

Dr. Patrick McGann from MRSN, WRAIR.

For a long time, researchers and public health officials have warned that the continued spread of resistant bacteria could significantly limit treatment options. Routine operations could become dangerous and life threatening, as could minor infections.

An urgent health response is currently in progress to isolate and prevent the spread of mcr-1. Active surveillance of such multidrug resistant bacteria enables earlier and more precise identification of the sources the bacteria have originated from. Researchers can use samples stored in MRSN’s growing repository to help identify trends in prevalence and resistance and establish best practices for healthcare providers.

Co-founder and Director of MRSN COL Emil Lesho says: "Through our surveillance system, we have the unique ability to coordinate source information with susceptibility and sequencing data, and if need be, go back to understand changes in infecting organisms to best treat infection and track emerging multidrug resistant organisms."