Genome sequences of two clinical Escherichia coli isolates harboring the novel colistin-resistance gene variants mcr-1.26 and mcr-1.27

BACKGROUND: Colistin is still a widely used antibiotic in veterinary medicine although it is a last-line treatment option for hospitalized patients with infections caused by multidrug-resistant Gram-negative bacteria. Colistin resistance has gained additional importance since the recent emergence of mobile colistin resistance (mcr) genes. In the scope of a study on colistin resistance in clinical Escherichia coli isolates from human patients in Germany we characterized the mcr-1 gene variants. RESULTS: Our PCR-based screening for mcr-carrying E. coli from German patients revealed the presence of mcr-1-like genes in 60 isolates. Subsequent whole-genome sequence-based analyses detected one non-synonymous mutation in the mcr-1 gene for two isolates. The mutations were verified by Sanger sequencing and resulted in amino acid changes Met1Thr (isolate 803-18) and Tyr9Cys (isolate 844-18). Genotyping revealed no relationship between the isolates. The two clinical isolates were assigned to sequence types ST155 (isolate 803-18) and ST69 (isolate 844-18). Both mcr-1 variants were found to be located on IncX4 plasmids of 33 kb size; these plasmids were successfully conjugated into sodium azide resistant E. coli J53 Azi(r) in a broth mating experiment. CONCLUSIONS: Here we present the draft sequences of E. coli isolate 803-18 carrying the novel variant mcr-1.26 and isolate 844-14 carrying the novel variant mcr-1.27. The results highlight the increasing issue of transferable colistin resistance.