Population structure and antimicrobial resistance traits of avian-origin mcr-1-positive Escherichia coli in Eastern China, 2015 to 2017.

Recent emergence of mcr-1-positive Escherichia coli (MCRPEC) is causing serious concern around the world. Due to poultry-origin E. coli holding zoonotic potential, the improved understandings of MCRPEC population structure and antimicrobial resistance are critical to public health purposes. This study provided novel insights into the molecular epidemiology of avian-origin MCRPEC. For the mcr genes prevalence study, we analysed 1,360 E. coli recovered from avian colibacillosis in eastern China from 2015 to 2017. The mcr-1 was present in 172 (12.6%) E. coli isolates. For all of MCRPEC isolates, MICs of colistin were ≥4 mg/L. Avian-origin MCRPEC was widely distributed throughout phylogroups A, B1, B2, D, and F. Moreover, those isolates were assigned to 52 unique STs, such as ST48, ST117, ST131, and ST648, suggesting substantial horizontal dissemination of mcr-1 gene through avian-origin E. coli populations. The susceptibility of MCRPEC isolates was tested with 26 antimicrobial agents from 16 antimicrobial categories. There were high resistance rates of MCRPEC isolates against the clinically used antibiotics. All MCRPEC isolates in this study presented the multidrug-resistant (MDR) trait were even considered as extensively drug-resistant (XDR) strains. Resistance genotypes and plasmid replicon profiling showed that a majority of MCRPEC isolates contained plasmid-mediated resistance genes and exhibited the co-existence of mcr-1 with ESBLs and pAmpCs genes. Furthermore, the overlapped distribution of ST types and resistance gene contents was detected among MCRPEC isolates from humans and poultry. Besides mcr-1, our findings highlighted a significant prevalence of plasmid-mediated resistance genes among avian-origin MCRPEC isolates.