Watch out! A One Health tale of colistin resistance transmission in a mixed farm

Colistin is a last resort antibiotic in human medicine. Under the umbrella of One-Health, we applied whole-genome sequencing to unravel the transmission of colistin resistance from livestock to the farmer on a mixed farm. Multidrug-resistant Escherichia coli isolated from pigs, calves, and a farmer also carried several virulence genes, such as Shiga-toxin or cytolethal distending toxin. Colistin resistance was due to the mcr-1 gene, carried on plasmids (IncX4, lncI2, and lncHl2) or the chromosome. Human IncX4 plasmid was most likely acquired from cattle (99.97% identity: 99.99% coverage). Livestock is a reservoir of plasmids with resistance genes concerning human health.