Mechanistic Insights of Colistin Resistance and Its Public Health Implications

Multi-drug resistance poses a serious threat to the public health worldwide. The situation becomes worse when multidrug-resistant bacteria develop resistance against last resort antibiotics such as colistin attributed to plasmid-borne mcr genes. Humans and non-human animals including pigs and chickens are the main reservoirs of these mcr genes harboring bacteria which have now disseminated globally, thus, causing difficulties in treating bacterial infections. Several mcr-gene-containing bacterial (MGCB) species have been found in diverse ecosystems, including aquatic, soil, botanical, wildlife, animal, and public environments. Environmental samples have shown to contain the mcr-1, mcr-2, mcr-3, mcr-5, mcr-7, and mcr-8 genes variants. The genes are found in Escherichia coli, Enterobacter, Klebsiella, Proteus, Salmonella, Citrobacter, Pseudomonas, Acinetobacter, Kluyvera, Aeromonas, Providencia, and Raulotella isolates. The routes of transmission of MGCB are contact with reservoirs that contain mcr, consumption of contaminated animal-/plant-based foods or water, trade and travel that involve animal-/plant-based foods. An updated and precise estimation of prevelance as well as mechanism of colistin resistance mediated by mcr genes is inevitable to regulate the spread of colistin resistance by implementing effective strategies. Hence, this review presents a comprehensive overview of epidemiology and the various mechanisms of colistin resistance that are currently not clearly understood.