Research note: characteristics of blaNDM and mcr-1 co-producing Escherichia coli from retail chicken meat

Carbapenems and colistin are vital antimicrobials used to treat Enterobacteriaceae-caused infections. The present study aimed to characterize the coexistence mechanism of carbapenem and colistin resistance in an Escherichia coli isolated from retail chicken meat. A total of 4 E. coli isolates co-harboring carbapenem resistance gene bla_NDM (2 E. coli isolates with bla_{NDM-5 and} 2 with bla_NDM-9) and colistin resistance gene mcr-1. Antimicrobial susceptibility testing exhibited that all the 4 E. coli strains had multidrug resistance profile and consistent with the resistance genes they carried. MLST showed that 3 E. coli isolates belonged to a pathogenic E. coli lineage ST354, which is closely associated with human infections and pose a serious threat to public health. Whole genome sequencing (WGS) showed that 4 mcr-1-positive plasmids with sizes of 60.4 kb to 67.4 kb all belonged to the IncI2 type. A total of 5 bla_NDM-harboring plasmids ranged from 99.0 kb to 138.3 kb, among which 4 plasmids belonged to unknow type and only pCS5L-NDM belonged to IncFIA/IncFIB group of hybrid plasmids, a novel carrier for bla_NDM. Comparative analysis exhibited that the mcr-1 or bla_NDM-carrying plasmids of E. coli strains from chicken meat showed high identity with that from Enterobacteriaceae of human origin, which indicated the risk of mcr-1 or bla_NDM dissemination from retail meat to human. The simultaneous occurrence of mcr-1 and bla_NDM in E. coli emphasizes the significant of antimicrobial resistance surveillance in retail meat.