Mobile colistin resistance (mcr) genes encoded on conjugative plasmids, although described only relatively recently, have been reported globally both in humans and livestock. The genes are often associated with the insertion sequence ISApl1 that can transpose the genes to novel genetic locations. Since its first report, multiple variants of mcr have been discovered in a variety of genetic locations in Escherichia coli, in plasmids and integrated into the chromosome. (Ardig project)