Manure as a Potential Hotspot for Antibiotic Resistance Dissemination by Horizontal Gene Transfer Events

Summary

This narrative review synthesises evidence on livestock manure as a critical environmental reservoir and vector for antibiotic resistance gene dissemination via horizontal gene transfer. The authors establish that manure's unique characteristics—high nutrient content, bacterial abundance and diversity, and residual antibiotics—create conditions favourable for ARG mobilisation and persistence, particularly through bacterial conjugation. The review concludes that current mitigation strategies reduce some but not all antimicrobials and resistant organisms, highlighting the need for integrated approaches to limit antimicrobial loads entering agricultural soils.

Regional applicability

Given the UK's intensive livestock production and widespread manure application to arable and grassland soils, these findings are directly relevant to UK farming practice and public health policy. The evidence supports calls for stronger regulations on antimicrobial use in UK livestock production and standards for manure treatment prior to soil application.

Key measures

Concentrations and diversity of antibiotic residues, antibiotic resistance genes (ARGs), and antibiotic-resistant bacteria in manure and manure-amended soils; efficacy of reduction methodologies; prevalence of conjugation events

Outcomes reported

This review analysed the role of manure in persistence and dissemination of antibiotic resistance genes (ARGs) in the environment, and evaluated reduction methodologies and public health impacts. The authors identified manure as a hotspot for horizontal gene transfer of antimicrobial resistance genes, characterised by nutrient richness, bacterial diversity, and selective pressure from antibiotic residues.

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