Dynamics and mitigation of antibiotic resistance genes during manure composting: A comprehensive review

The global spread of antibiotic resistance genes (ARGs) poses a significant threat to public health, facilitated by the extensive use of antibiotics in livestock production and the subsequent environmental dissemination of ARGs through animal manure. Manure composting has emerged as a widely adopted strategy for manure management and pathogen reduction; however, its effectiveness in mitigating ARGs remains variable and dependent on specific conditions. This review provides a comprehensive synthesis of the current state of knowledge and understanding of the fate of ARGs during manure composting processes, highlighting the influence of key factors, including temperature, pH, carbon-to-nitrogen ratio, aeration, and moisture content, on ARG dynamics. It further explores the roles of microbial community shifts, horizontal gene transfer, and mobile genetic elements in ARG persistence and attenuation, alongside recent advancements in composting technologies that show promise in ARG mitigation such as hyperthermophilic composting, biochar amendment, electrokinetic and magnetic field-assisted composting, and microbial inoculation, The review also highlights the limitations of current practices, including the potential for ARG resurgence during later composting stages and the lack of standardized evaluation protocols. Finally, it identifies critical research gaps and proposes future directions centered on integrated mitigation strategies, long-term field assessments, and the development of risk assessment frameworks. These insights aim to guide researchers, policymakers, and stakeholders in improving composting practices to curb the dissemination of ARGs and safeguard environmental and public health. This review highlights composting as a promising strategy for reducing ARGs in manure, while identifying knowledge gaps related to long-term ecological impacts and optimal operational conditions.