A novel deletion mutation in pmrB contributes to concurrent colistin resistance in carbapenem resistant E. coli ST 405 of clinical origin.

We report the first clinical Escherichia. coli strain EC3000 with concomitant chromosomal colistin and carbapenem resistance. A novel in-frame deletion, Delta6-11(RPISLR), in pmrB contributing to colistin resistance was verified using recombinant DNA techniques. Although decreased fitness compared to the wild-type (WT) strain or EC3000 revertant (chromosomal replacement of WT pmrB in EC3000), a portion of serially passaged EC3000 strains preserving colistin resistance without selective pressure raises the concern for further spread.