Genomic features of a high-risk mcr-1.1-positive Escherichia coli ST10 isolated from cattle farm environment.

The environment plays an important role in the dissemination of clinically relevant antimicrobial-resistant bacteria and genes. In this study, we described genomic features of a plasmid-mediated colistin-resistant mcr-1-positive Escherichia coli strains (PK-3225) isolated from a dairy farm wastewater sample. After initial isolation and PCR detection of mcr-1-positive E. coli, whole-genome sequencing was performed using Illumina Hiseq 2500 followed by in silico analysis. Genetic context surrounding the mcr-1 gene was determined and SNP-based phylogenomic analysis was performed. Furthermore, plasmid analysis and conjugation assays were performed to determine transferability of mcr-1. E. coli PK-3225 belonged to ST10 and carried a broad resistome that included colistin (mcr-1), beta-lactam (bla), tetracycline (tetB), phenicol (catA1), macrolide (mdfA), trimethoprim (dfrA17), aminoglycosides (aadA5, aph(3")-Ib, aph(6)-Id), and sulphonamide (sul2) resistance genes. The draft genome of E. coli calculated as 4.9 Mbp. Conjugation experiment showed successful transfer of the mcr-1 gene to E. coli recipient strain J53. In silico analysis showed that mcr-1 was located on IncI2 plasmid of > 59 kb in length, with the nikB-mcr-1-pap2 gene array, and lack ISApl1. The phylogenomic analysis revealed that the PK-3225 was closely related to human ST10 E. coli from Brazil and USA. To our knowledge, this is the first draft genome sequence of mcr-1 carrying E. coli isolated from the farm environment in Pakistan. Considering the high burden of colistin resistance in Pakistan, presence of pandemic high-risk E. coli clones in the environment requires strict surveillance.