In this work, authors investigated the prevalence of mcr-mediated colistin resistance in Escherichia coli isolated from healthy food-producing animals from 2012 to 2016 in Belgium.
They studied the resistance profile, the plasmid type and the sequence type of these isolates. Overall, 40 E. coli carried at least one mcr gene, the mcr-1 being the most frequent followed by mcr-4, mcr-2, mcr-3 and mcr-5. Thirty three isolates had a multidrug-resistant (MDR) phenotype, with resistance to ampicillin, tetracycline, sulfamethoxazole, trimethoprim and ciprofloxacin being the most frequent.
No specific clonal lineage of E. coli was identified and mcr genes were carried on different plasmid types. Interestingly, one MDR E. coli carried three mcr genes: mcr-1, mcr-3 and mcr-5. This isolate was co-resistant to all antimicrobial tested excepted meropenem and tigecycline. Twenty seven antibiotic resistance genes were identified and seven different plasmid replicons.
This work reveals the high prevalence and circulation of mcr genes in food-producing animals in Belgium. Some isolates are MDR and carry multiple antibiotic resistance genes and plasmids that can be easily transferrable to other isolates of the same species or other species.
The presence of multiple mcr genes in one isolate is intriguing and suggests that those genes may have functions other than resistance to colistin only. Global surveillance programmes and antibiotic stewardship are warranted to prevent the emergence and spread of MDR isolates in humans, animals and environment.