Emergence of a multidrug-resistant ST 27 Escherichia coli co-harboring bla, mcr-1, and fosA3 from a patient in China.

In this study, we report a clinical isolate of a carbapenem-, colistin-, and fosfomycin-resistant Escherichia coli isolate DC-3737 co-harboring bla, mcr-1, and fosA3 from an inpatient in China. Antimicrobial susceptibility testing, polymerase chain reaction, multi-locus sequence typing, conjugation experiment, and Southern blot hybridization were performed on E. coli DC-3737 isolated from the wound. Plasmid analysis is presented and the locations of bla, mcr-1, fosA3, and other resistance genes were identified as well. E. coli DC-3737 was resistant to ampicillin, ceftriaxone, ceftazidime, ciprofloxacin, levofloxacin, gentamicin, tobramycin, trimethoprim-sulfamethoxazole, imipenem, meropenem, ertapenem, fosfomycin and colistin, and with intermediate susceptibility to amikacin. It was typed as sequence type 27. The isolate possessed bla, mcr-1, fosA3, bla, bla, aac (6')-Ib-cr and sul1 simultaneously. In addition, the mutations in quinolone resistance-determinant regions (QRDRs) such as Ser83Leu and Asp87Asn in gyrA, and Ser80Ile in parC were detected. Conjugation assays revealed that bla, fosA3, sul1, mcr-1, and bla genes could successfully transfer their resistance phenotype to E. coli strain J53. Plasmid analysis and Southern hybridization showed that DC-3737 possessed Z-type self-transmissible plasmid bearing bla, fosA3, and sul1. Moreover, mcr-1, bla, and bla were located on a ~60-kb IncFIB type self-transmissible plasmid. This is the first report of bla, mcr-1 and fosA3 co-harboring in E. coli in China. Moreover, it is also the first description of the co-harboring of bla and fosA3 in a single Z plasmid in Enterobacteriaceae species. The identification of E. coli DC-3737 co-harboring bla, mcr-1, and fosA3 in this study highlights the need to increase epidemiologic surveillance and the need for new classes of antibiotics to address multidrug-resistant bacteria.