A Novel Deletion Mutation in <i>pmrB</i> Contributes to Concurrent Colistin Resistance in Carbapenem-Resistant Escherichia coli Sequence Type 405 of Clinical Origin

Abstract

We report the first clinical <i>Escherichia coli</i> strain EC3000 with concomitant chromosomal colistin and carbapenem resistance. A novel in-frame deletion, Δ6-11 (RPISLR), in <i>pmrB</i> that contributes to colistin resistance was verified using recombinant DNA techniques. Although being less fit than the wild-type (WT) strain or EC3000 revertant (chromosomal replacement of WT <i>pmrB</i> in EC3000), a portion of serially passaged EC3000 strains preserving colistin resistance without selective pressure raises the concern for further spread.