“Tracking the mcr gene”
“About mcr Genes, an Emerging Threat
The mcr-1, mcr-2 and mcr-3 genes cause resistance to colistin, a last-resort antibiotic used for treating resistant infections. Colistin is considered a last-resort antibiotic because—while it can be used to treat patients with infections that have already developed resistance to other antibiotics—it can have serious side effects.
The mcr gene is particularly worrisome because it is found on plasmids, small pieces of DNA that carry genetic instructions from one bacterium to another. This means that plasmids carrying resistant mcr genes can make other bacteria become resistant to colistin, including the “nightmare bacteria” carbapenem-resistant Enterobacteriaceae (CRE). The term mcr stands for “plasmid-mediated colistin resistance,” describing the gene’s ability to avoid the effects of colistin and share this ability with other bacteria. The descriptions -1, -2, and -3 indicate different DNA sequences.
The mcr gene has been found in food animals and in people since it was first reported in November 2015. The first mcr-1 gene was reported by China in November 2015, followed by Belgium’s report on the first mcr-2 in July 2016. In June 2017, an article published in mBio, an open access journal published by the American Society for Microbiology, described finding the first mcr-3. “