Abstract
The mobile colistin resistance (mcr) gene threatens the efficacy of colistin (COL), a last-line antibiotic used in treating deadly infections. For more than six decades, COL is used in livestock around the globe, including Africa. The use of critically important antimicrobial agents, like COL, is largely unregulated in Africa, and many other factors militate against effective antimicrobial stewardship in the continent. Currently, ten mcr genes (mcr-1 to mcr-10) have been described. In Africa, mcr-1, mcr-2, mcr-3, mcr-5, mcr-8, and mcr-9 have been detected in isolates from humans, animals, foods of animal origin, and the environment. These genes are harboured by Escherichia coli, Klebsiella, Salmonella, Citrobacter, Enterobacter, Pseudomonas, Aeromonas, Alcaligenes, and Acinetobacter baumannii isolates. Different conjugative and nonconjugative plasmids form the backbone for mcr in these isolates; however, mcr-1 and mcr-3 have also been integrated into the chromosome of some African strains. Insertion sequences (ISs) (especially ISApl1), either located upstream or downstream of mcr, class 1 integrons, and transposons, are drivers of mcr in Africa. Genes coding multi/extensive drug resistance and virulence are colocated with mcr on plasmids in African strains. Transmission of mcr to/among African strains is nonclonal. Contact with mcr-habouring reservoirs, the consumption of contaminated foods of animal/plant origin or fluid, animal-/plant-based food trade and travel serve as exportation, importation, and transmission routes of mcr gene-containing bacteria in Africa. Herein, the current status of plasmid-mediated COL resistance in humans, food-producing animals, foods of animal origin, and environment in Africa is discussed.
Highlights
Colistin (COL) is one of the few last-line antibiotics used in treating deadly infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gramnegative bacilli (GNB)
The use of COL in humans was largely abandoned in the 1970s due to its neurotoxic and nephrotoxic effects alongside to the discovery and approval of new and effective antibiotics [2], but COL has been used in livestock for more than six decades in most countries in the world, including Africa [3,4,5]
Isolates from the Tunisian poultry sector carried mcr-1 on diverse plasmids (IncHI2, IncI2, 242 kb IncP, and IncFIB) [32, 34, 39], and they possessed class 1 integrons and 21 antibiotic resistance genes belonging to four antimicrobial families [24, 32, 34, 37, 39] while transposon ISApl1 was upstream of mcr-1 which was carried on IncHI2 plasmid in isolates from the Algerian poultry sector [28]. These findings suggest that diverse mobile genetic elements (MGEs) facilitate the acquisition and transfer of mcr-1 in North Africa
Summary
Colistin (COL) is one of the few last-line antibiotics used in treating deadly infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gramnegative bacilli (GNB). Understanding the epidemiology, phenotypic, and genotypic characteristics of mcr-carrying isolates, the genetic context of mcr in the isolates, and population structure and mechanism of acquisition of mcr genes by organisms in Africa creates the needed impetus to tackle the problem to reduce the risk to public health [19] This current review articulates the findings of studies on plasmid-mediated COL resistance among isolates from different food-producing animals, foods of animal origin, humans, and environment in Africa.
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