Rebound of Antibiotic Resistance Genes in Composting: Mechanisms, Challenges, and Control Strategies

The proliferation of antibiotic resistance genes (ARGs) in livestock manure has raised growing environmental and public health concerns. Composting is widely recognized as an effective method to mitigate ARG dissemination; however, recent studies have increasingly reported a rebound in ARG abundance during the curing stage of composting, undermining its long-term effectiveness. Here, “rebound” refers to a renewed increase in ARG abundance—either in absolute terms or relative to the 16S rRNA gene—following its decline to a minimum during the thermophilic phase. This review systematically summarizes the dynamic changes in ARGs throughout the composting process, with a particular focus on the mechanisms and drivers underlying ARG rebound. Vertical and horizontal gene transfer, along with microbial succession, are discussed as key contributors to this phenomenon. Current strategies to suppress ARG rebound, including microbial community manipulation, hyperthermophilic composting, and exogenous amendments, are evaluated. Furthermore, the roles of heavy metals and extracellular polymeric substances in promoting ARG persistence are examined, highlighting their potential involvement in ARG rebound. This review aims to provide a comprehensive understanding of ARG rebound in composting and to inform the development of more effective, integrated mitigation strategies.