Abstract
Colistin use has mostly been stopped in human medicine, due to its toxicity. However, nowadays, it still is used as a last-resort antibiotic to treat hospital infections caused by multi-drug resistant Enterobacteriaceae. On the contrary, colistin has been used in veterinary medicine until recently. In this study, 210 fecal samples from pigs (n = 57), calves (n = 152), and the farmer (n = 1) were collected from a farm where E. coli harboring mcr-1–mcr-3 was previously detected. Samples were plated, and mcr-genes presence was confirmed by multiplex-PCR. Hybrid sequencing which determined the presence and location of mcr-1, other antibiotic resistance genes, and virulence factors. Eighteen colistin resistant isolates (13 from calves, four from pigs, and one from the farmer) contained mcr-1 associated with plasmids (IncX4, IncI2, and IncHI2), except for two that yielded mcr-1 in the chromosome. Similar plasmids were distributed in different E. coli lineages. Transmission of mcr-1 to the farmer most likely occurred by horizontal gene transfer from E. coli of calf origin, since plasmids were highly similar (99% coverage, 99.97% identity). Moreover, 33 virulence factors, including stx2 for Shiga toxin E. coli (STEC) were detected, highlighting the role of livestock as a reservoir of pathotypes with zoonotic potential.
Highlights
The vast majority of antimicrobials used in veterinary medicine are used in human medicine
The consumption of antimicrobial agents has increased the selection of resistant bacteria in both human and veterinary medicine
The multiplex PCR confirmed the presence of mcr-1 in the 18 E. coli isolates (13 from calves, four from pigs and one from the farmer)
Summary
The vast majority of antimicrobials used in veterinary medicine are used in human medicine. The consumption of antimicrobial agents has increased the selection of resistant bacteria in both human and veterinary medicine. Use of colistin in human medicine has been abandoned, due to its toxicity when applied systemically. Studies performed in different EU countries have reported the prophylactic and metaphylactic use of colistin for the prevention and treatment of enteric diarrheas in pigs [3,4,5,6]. In this scenario, Spain was the country with the highest sales of colistin for food-producing animals in the EU in 2014 [7]. Colistin consumption has been drastically reduced in the last years after the implementation of a specific program “Reduce Colistin”, targeting pig production with the voluntary agreement of producers [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
