A team of researchers in Belgium is reporting the discovery of a new gene distinct from MCR-1 that can confer colistin resistance in Escherichia coli samples taken from cows and pigs.
The authors of the report, published today in the journal Eurosurveillance, said the gene—which they are calling MCR-2—was detected on plasmids from 3 of 10 colistin-resistant E coli isolates taken from calves and piglets in Belgium.
Those isolates had been randomly selected from 92 bovine and porcine colistin-resistant E coli isolates that did not show the presence of the MCR-1 gene, which was first identified in E coli samples in China in late 2015 and has now been detected in 30 countries.
The MCR-1 gene has raised alarms among public health officials because it enables bacteria to disable colistin, a last-resort antibiotic that is used to treat highly resistant bacteria. In addition, because the genes are carried on plasmids, which are highly mobile pieces of DNA, they can be easily copied and transferred between different strains of bacteria and therefore have the potential to spread rapidly in both animals and humans.
In May, US health officials announced that the MCR-1 gene had been detected in the urine of a 49-year-old Pennsylvania woman with E coli. The gene has also been found in Klebsiella pneumoniae and carbapenem-resistant Enterobacteriaceae samples. Last week, researchers in Portugal reported on the detection of MCR-1 genes in Salmonella isolates.
Ability to spread rapidly
Now it appears that there is another gene capable of conferring colistin resistance. The authors of the study said a phylogenic analysis of MCR-2 provided strong evidence that the gene is distinct from MCR-1, and that it might have originated from Moraxella catarrhalis, an exclusively human pathogen that is a common cause of ear infections in infants. Their experiments also indicated that the MCR-2 gene may be able to spread more rapidly than MCR-1
"They showed that this has a higher transfer frequency, so this thing has the potential to disseminate more quickly than mcr-1," Lance Price, PhD, director of the Antibiotic Resistance Action Center at George Washington University, told the medical news service Stat.
The authors are calling for immediate inclusion of MCR-2 in ongoing molecular epidemiologic surveillance of colistin-resistant pathogens in the food supply and in humans.
Jul 7 Eurosurveill report
Jul 7 Stat story
Jul 1 CIDRAP News story on MCR-1 in Portugal