Colistin: from the shadows to a One Health approach for addressing antimicrobial resistance.

Antimicrobial resistance (AMR) poses a serious threat to human, animal and environmental health worldwide. Colistin has regained importance as a last-resort treatment against multi-drug-resistant Gram-negative bacteria. However, colistin resistance has been reported in various Enterobacteriaceae species isolated from several sources. The 2015 discovery of the plasmid-mediated mcr-1 (mobile colistin resistance) gene conferring resistance to colistin was a major concern within the scientific community worldwide. The global spread of this plasmid - as well as the subsequent identification of 10 MCR-family genes and their variants that catalyse the addition of phosphoethanolamine to the phosphate group of lipid A - underscores the urgent need to regulate the use of colistin, particularly in animal production. This review traces the history of colistin resistance and mcr-like gene identification, and examines the impact of policy changes regarding the use of colistin on the prevalence of mcr-1-positive Escherichia coli and colistin-resistant E. coli from a One Health perspective. The withdrawal of colistin as a livestock growth promoter in several countries reduced the prevalence of colistin-resistant bacteria and its resistance determinants (e.g. mcr-1 gene) in farm animals, humans and the environment. This reduction was certainly favoured by the significant fitness cost associated with acquisition and expression of the mcr-1 gene in enterobacterial species. The success of this One Health intervention could be used to accelerate regulation of other important antimicrobials, especially those associated with bacterial resistance mechanisms linked to high fitness cost. The development of global collaborations and the implementation of sustainable solutions like the One Health approach are essential to manage AMR.