mcr-3 and mcr-4 Variants in Carbapenemase-Producing Clinical Enterobacteriaceae Do Not Confer Phenotypic Polymyxin Resistance

Abstract

The worldwide distribution of plasmid-mediated colistin resistance determinants (mcr-1, mcr-2, mcr-3, and mcr-4) coupled to the emerging observation that colistin resistance is more prevalent in carbapenem-resistant Enterobacteriaceae (CRE) (1, 2) presents a daunting challenge in combatting antimicrobial resistance. Undoubtedly, next-generation sequencing approaches have expedited the discovery of mobile colistin resistance determinants (3). In this study, we undertook the in silico screening of 500 phenotypically carbapenem-resistant carbapenemase-producing Enterobacteriaceae whole genomes for the presence of the mcr gene, using CLC Genomics Workbench (CLC Bio-Qiagen, Aarhus, Denmark). The isolates comprised clinical and screening pure cultures submitted to the national reference laboratory for mandatory CRE surveillance. Locally, the presence of mcr-1 as well as its cocarriage with KPC-2 had been previously well described (4, 5); hence, we did not look further into the distribution of mcr-1. mcr-2 was not detected among the genomes analyzed. mcr-3 was identified in one Escherichia coli genome (ENT1955) by the use of both read mapping and de novo assembly.