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Plasmid-mediated colistin-resistance genes have been reported worldwide in recent years. A multiplex polymerase chain reaction (Multi-PCR) protocol was developed to detect transferable colistinresistance genes (mcr-1 to mcr-6) in Enterobacteria for clinical laboratory purposes.The authors first designed six new primer pairs to amplify mcr-1 to mcr-6 gene products to achieve stepwise separation of amplicons between 87 to 216 bp,then divided these primers into two subgroups with the assistance of a pair of universal primers for the detection of currently described mcr genes and their variants in Enterobacteria. The protocol was validated by testing 29 clinical isolates of Escherichia coli of human origin, each well characterised and prospectively validated. The Multi-PCR assay showed full concordance with whole-genome sequence data and displayed higher sensitivity and 100% specificity. The assay could detect all variants of the various mcr alleles described. It was able to detect mcr-3 and mcr-4 as singletons or in combination. This type of test is critical for the epidemiological surveillance of plasmid-encoded resistance in limited resources conditions, and this method allows rapid identification of mcr-positive bacteria and overcomes the challenges of phenotypic detection of colistin resistance.

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