Mobile Colistin Resistance Genes in Africa: A One Health Narrative Review of Reservoirs, Drivers, Transmission Pathways, and Knowledge Gaps

Background/Objectives: Colistin has re-emerged as a critical last-resort antimicrobial for treating infections caused by multidrug-resistant Gram-negative bacteria. The discovery of plasmid-mediated mobile colistin resistance (mcr) genes in 2015 fundamentally changed the understanding of colistin resistance by demonstrating its capacity for horizontal transfer across bacterial species, hosts, and environments. Since then, increasing evidence has documented the widespread occurrence of mcr genes across Africa, threatening the long-term effectiveness of colistin. Earlier reviews have largely addressed single sectors or regions; here, we integrate all sectors, distinguish direct detection from inferred transmission, and propose prioritised actions. Methods: This narrative review synthesises current evidence on mobile colistin resistance in Africa through a One Health lens, integrating findings from human, animal, food, wildlife, and environmental sectors. Results: We provide a comprehensive overview of the molecular mechanisms, epidemiology, transmission pathways, and drivers of mcr dissemination across the continent. Available evidence indicates that mcr genes, particularly mcr-1, are distributed among clinical isolates, livestock, retail food products, wastewater, surface waters, agricultural soils, and wild birds, which is consistent with connected transmission across sectors. Key drivers include inappropriate antimicrobial use, livestock intensification, inadequate wastewater treatment, environmental contamination, climate change, and human and animal mobility. Conclusions: The frequent association of mcr genes with mobile genetic elements and other antimicrobial resistance determinants facilitates their persistence through horizontal gene transfer and co-selection. Despite increasing recognition of this threat, major gaps remain in surveillance, genomic characterisation, environmental monitoring, and understanding of transmission dynamics. Addressing these challenges will require stronger One Health surveillance, antimicrobial stewardship, genomic monitoring, improved environmental management, and coordinated policy interventions to mitigate the spread of mobile colistin resistance and preserve the clinical utility of colistin across Africa.