First Discovery in U.S. of Colistin Resistance in Human E. coli Infection

Finding may herald emergence of pan–drug-resistant bugs

The Multidrug Resistant Organism Repository and Surveillance Network (MRSN) at the Walter Reed Army Institute of Research (WRAIR) has characterized a transferrable gene for colistin resistance in the United States that may herald the emergence of truly pan–drug-resistant bacteria.

The finding was published in Antimicrobial Agents and Chemotherapy, a journal of the American Society for Microbiology

Colistin is the last agent used to combat bacteria that are resistant to the strongest antibiotics. Colistin has remained the best tool available to treat multidrug-resistant bacteria because bacteria were not exchanging genes for its resistance. This latest discovery shows that colistin may be losing its effectiveness in antimicrobial therapy. Now, bacteria may be exchanging resistance genes for colistin.

Alarms sounded in the microbiology community in late 2015 when the first transferrable gene for colistin resistance was identified in China. Since that report, the global health community has monitored and searched for the occurrence of this gene in the food supply and in humans. The colistin-resistance gene has been found in Europe and Canada, and is now reported in the U.S.

A clinical sample from a urinary-tract infection was collected from a patient in a military treatment facility in Pennsylvania. The sample was sent to the Walter Reed National Military Medical Center (WRNMMC), where colistin susceptibility was tested. The results showed that no safe dosage of colistin would be effective to treat such a bacterial infection. The WRNMMC recognized colistin resistance and sent a sample to the WRAIR’s MRSN in Bethesda, Maryland, for sequencing, which identified the colistin-resistant gene mcr-1.

“Colistin is one of the last efficacious antibiotics for the treatment of highly resistant bacteria. 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 health care community and beyond is critical to prevent its spread,” said Dr. Patrick McGann, MRSN, WRAIR.

Through intergovernmental communication, it was learned that the Centers for Disease Control and Prevention (CDC) and the U.S. Department of Agriculture (USDA) are also reporting a swine intestinal infection with a single mcr-1–positive Escherichia coli strain. While there is no evidence that links these recent findings, the evidence of the strain in the U.S. is a public health concern. The gene is transferrable to other bacteria, which could worsen the current global crisis of antimicrobial resistance.

Source: EurekAlert; May 26, 2016.