Back-Mixing Accelerates Pleuromutilin Degradation and Improves the Composting Performance of Pleuromutilin Mycelial Residue Without Aggravating Antibiotic Resistance Risk

Back-mixing has been widely applied during practical composting to initiate the process and improve compost product quality. However, for antibiotic mycelial residue (AMR), a fermentation by-product containing residual antibiotics, the ecological safety of this treatment remains unclear. In this study, pleuromutilin mycelial residue (PMR) was subjected to a 35-day aerobic composting experiment with a back-mixing treatment (T group) and the conventional composting group (CK group) to evaluate composting performance and antibiotic resistance risk. The results demonstrated that the T group exhibited more rapid heating and a higher degree of humification. Additionally, the T group not only exhibited faster pleuromutilin degradation, reaching below the detection limit 3 days earlier than in the CK group, but also achieved up to a 3.1-fold reduction in antibiotic resistance genes (ARGs) and a 93.2% overall reduction in mobile genetic elements (MGEs). Redundancy analysis (RDA), variance partitioning analysis (VPA), and co-occurrence network analysis indicated that microbial community structure appeared to be more strongly associated with ARG variation than MGEs under the tested conditions. Overall, back-mixing accelerated pleuromutilin degradation and enhanced PMR composting performance, while no substantial enrichment of the detected ARGs was observed under the tested composting conditions. This study provides a scientific basis for the safe resource utilization of AMR.