Genome sequences of two clinical isolates harboring the novel colistin-resistance gene variants - and -.

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 () genes. In the scope of a study on colistin resistance in clinical isolates from human patients in Germany we characterized the - gene variants.

Results: Our PCR-based screening for -carrying from German patients revealed the presence of -- genes in 60 isolates. Subsequent whole-genome sequence-based analyses detected one non-synonymous mutation in the - 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 - variants were found to be located on IncX4 plasmids of 33 kb size; these plasmids were successfully conjugated into sodium azide resistant J53 Azi in a broth mating experiment.

Conclusions: Here we present the draft sequences of isolate 803-18 carrying the novel variant - and isolate 844-14 carrying the novel variant -. The results highlight the increasing issue of transferable colistin resistance.