Emergence of Incl2 plasmid-mediated colistin resistance in avian Escherichia fergusonii

The high antimicrobial resistance rate of E. fergusonii may herald a novel reservoir of AMR genes and IncI2 plasmid may be an important factor affecting mcr-1 transfer in poultry. Escherichia fergusonii, an opportunistic zoonotic pathogen, has a greatly increased importance in public health with the discovery of cephalosporin- and colistin-resistant strains. The IncHI2 plasmid carrying mcr-1 has been reported in E. fergusonii, but the other types of plasmids carrying mcr-1 have never been reported. In this study, 268 samples of cecal contents or anal swabs were collected from slaughterhouses and farms in two cities in Zhejiang, China, where 54 E. fergusonii strains (18.88%) were isolated between 2020 and 2021. To our knowledge, this is the first report of the isolation of E. fergusonii in meat ducks (slaughterhouse). The minimum inhibitory concentration (MIC) of isolates was determined by the broth microdilution method, in which it was determined that the tetracycline resistance rate was the highest (83.33%) and the multidrug-resistance (MDR) rate was 75.93%. A total of four strains of colistin-resistant E. fergusonii were found and identified as mcr-1-positive by PCR. Importantly, these strains could transfer the mcr-1 gene to strain E. coli J53 by conjugation. Genome sequencing revealed that the mcr-1 genes of the above four strains were all located on the Incl2 plasmid, and the mobile element ISApl1 upstream of mcr-1 was missing. Moreover, the plasmid pEF45-4 (61 140 bp) harboring mcr-1 in strain EF20JDJ4045 was revealed by Oxford Nanopore Technology, showing high homology with the previously reported in E. coli. Taken together, the high antimicrobial resistance (AMR) rate of E. fergusonii may herald a novel reservoir of AMR genes and IncI2 plasmid may be an important factor affecting mcr-1 transfer in poultry.