Plasmid-borne colistin resistance gene mcr-3 in Salmonella isolates from human infections.. mcr-3

In June 2017, Yin et al. reported a third plasmid-borne colistin resistance gene (encoded by mcr-3) in Escherichia coli from China [1]. The same study identified a truncated transposon element immediately upstream of mcr-3 that was also found in E. coli, Klebsiella pneumoniae and Salmonella Typhimurium [1]. This followed reports from 2016 on the plasmid-borne colistin resistance genes mcr-1 [2] and mcr-2 [3] and the subsequent reporting of global spread of mcr-1 and detection of mcr-1 from livestock/retail meat and human sources [4,5]. The worldwide spread of plasmid-mediated colistin resistance is of major concern, as colistin in some instances is the drug of last resort for multidrug-resistant infections.