Abstract
The emergence and spread of mobile colistin (COL) resistance (mcr) genes jeopardize the efficacy of COL, a last resort antibiotic for treating deadly infections. COL has been used in livestock for decades globally. Bacteria have mobilized mcr genes (mcr-1 to mcr-9). Mcr-gene-containing bacteria (MGCB) have disseminated by horizontal/lateral transfer into diverse ecosystems, including aquatic, soil, botanical, wildlife, animal environment, and public places. The mcr-1, mcr-2, mcr-3, mcr-5, mcr-7, and mcr-8 have been detected in isolates from and/or directly in environmental samples. These genes are harboured by Escherichia coli, Enterobacter, Klebsiella, Proteus, Salmonella, Citrobacter, Pseudomonas, Acinetobacter, Kluyvera, Aeromonas, Providencia, and Raulotella isolates. Different conjugative and non-conjugative plasmids form the backbones for mcr in these isolates, but mcr have also been integrated into the chromosome of some strains. Insertion sequences (IS) (especially ISApl1) located upstream or downstream of mcr, class 1–3 integrons, and transposons are other drivers of mcr in the environment. Genes encoding multi-/extensive-drug resistance and virulence are often co-located with mcr on plasmids in environmental isolates. Transmission of mcr to/among environmental strains is clonally unrestricted. Contact with the mcr-containing reservoirs, consumption of contaminated animal-/plant-based foods or water, international animal-/plant-based food trades and travel, are routes for transmission of MGCB.
Highlights
The emergence and spread of plasmid-mediated movable colistin (COL) resistance genes jeopardize the efficacy of COL considered a last resort drugs for treating deadly infections caused by multi- and extensively drug-resistant Gram-negative bacilli (GNB) [1,2]
A surveillance study on dissemination of mcr and carbapenem resistance in Chinese poultry production sector detected mcr-1 in sewage sample from a poultry farm, and an enterobacterial isolate carrying mcr-1 on IncI plasmid was obtained from the sample [86], further suggesting that IncI plasmid is a major driver of COL resistance in livestock environment and that animal farm wastes constitute a reservoir for Mcr-gene-containing bacteria (MGCB)
ST10 complex) [70,73], posing health challenge to the public. These findings strongly suggest that in China, colistin-resistant organisms (COLROS) are circulating within the animal-human-environmental ecosystem because isolates in ST10 complex are the most common faecal E. coli strains detected in humans in China [62,112]
Summary
The emergence and spread of plasmid-mediated movable colistin (COL) resistance (mcr) genes jeopardize the efficacy of COL considered a last resort drugs for treating deadly infections caused by multi- and extensively drug-resistant Gram-negative bacilli (GNB) [1,2]. There is an avalanche of publications in the literature showing that worldwide, humans and animals (especially livestock) are colonized by commensal and potentially pathogenic colistin-resistant organisms (COLROS)/mcr gene-containing bacteria (MGCB) [16,17,18]. Information on the occurrence, phenotypic and genotypic characteristics of MGCB isolated from the environment is crucial for an understanding of the epidemiology, genetic environment and mechanism of acquisition of mcr genes by environmental isolates Such information would be necessary in designing and prioritizing surveillance programs that may generate essential data for performing risk assessment, implementation of effective antimicrobial stewardship plans, developing effective strategies for control of COLROS, and reducing the risk to public health.
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