Molecular epidemiology and genomic characterization of a plasmid-mediated mcr-10 and blaNDM-1 co-harboring multidrug-resistant Enterobacter asburiae

Colistin is considered as one of the last-resort antimicrobial agents for treating multidrug-resistant bacterial infections. Multidrug-resistant E. asburiae has been increasingly isolated from clinical patients, which posed a great challenge for antibacterial treatment. This study aimed to report a mcr-10 and blaNDM-1 co-carrying E. asburiae clinical isolate 5549 conferred a high-level resistance against colistin. Antibiotic susceptibility testing was performed using the microdilution broth method. Transferability of mcr-10 and blaNDM-1-carrying plasmids were investigated by conjugation experiments. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to identify modifications in lipid A. Whole genome sequencing and phylogenetic analysis between strain 5549 and a total of 301 E. asburiae genomes retrieved from NCBI database were performed. The genetic characteristics of mcr-10 and blaNDM-1-bearing plasmids were also analyzed. Our study indicated that strain 5549 showed extensively antibiotic-resistant trait, including colistin and carbapenem resistance. The mcr-10 and blaNDM-1 were carried by IncFIB/IncFII type p5549_mcr-10 (159417 bp) and IncN type p5549_NDM-1 (63489 bp), respectively. Conjugation assays identified that only the blaNDM-1- carrying plasmid could be successfully transferred to E. coli J53. Interestingly, mcr-10 did not mediate colistin resistance when it was cloned into E. coli DH5 & alpha;. Mass spectrometry analysis showed the lipid A palmitoylation of the C-lacyl-oxo-acyl chain to the chemical structure of lipid A at m/z 2063 in strain 5549. In summary, this study is the first to report a mcr-10 and blaNDM-1 co-occurrence E. asburiae recovered from China. Our investigation revealed the distribution of different clonal lineage of E. asburiae with epidemiology perspective and the un-derlying mechanisms of colistin resistance. Active surveillance is necessary to control the further dissemination of multidrug-resistant E. asburiae.