Enterobacter hormaechei Genome sequencing and assembly. Enterobacter hormaechei

Antimicrobial resistance in Enterobacter species represents a global threat to the public health. In this study, we used whole-genome sequencing (WGS) to characterize two colistin susceptible Enterobacter cloacae isolates from milk of dairy cows diagnosed with clinical mastitis in a Brazilian dairy herd in 2011. The two strains carried an IncHI2A- pST1 plasmid, which has been associated with mcr genes globally. The two-component regulatory system genes qseBC were not detected, and the mcr-9 gene was flanked by two insertion sequences (IS903 and IS26). In comparison to mcr-9 published protein sequences, no database entry had 100% identity with original sequences reported. Three published protein sequences shared the highest identities with our sequences (99.81%), which differed by a threonine at position 282 that was present in our strains. In silico protein analysis suggested comparable 3D structures of alpha helixes involved, despite of the residue mutation. Additionally, the virulence profile of our strains harboring the new mcr-9 variant was investigated in vivo using a Galleria mellonella model. Both strains killed 60% of the larvae at 106 CFU/larva and demonstrated a higher mortality rate than E. cloacae ATCC 35030. To the best of our knowledge, this is the first report of mcr-9-positive bacteria from dairy farms.