Spread of colistin resistance gene mcr-1 in Italy: characterization of the mcr-1.2 allelic variant in a colistin-resistant blood isolate of Escherichia coli.

mcr-1.2, an allelic variant of the transferable colistin resistance gene mcr-1, was characterized in a colistin-resistant blood isolate of Escherichia coli. It was harbored by an IncX4-type plasmid (33,293 bp). Despite its low prevalence, the potentially worrying spread of the mcr-1 gene, particularly its mcr-1.2 variant, in Italy requires increasing surveillance.