Influence mechanism of sludge composting on antibiotic resistance genes under antibiotic stress: A comprehensive analysis

Antibiotic resistance genes (ARGs) are increasingly recognized as emerging contaminants that enter agricultural lands and surrounding ecosystems through the application of sewage sludge containing residual antibiotics. Composting is an effective method for reducing antibiotics and ARGs in sludge; however, the impact of residual antibiotics on the efficiency of ARG removal remains unclear. This study explored the reduction of oxytetracycline (OTC), sulfamerazine (SM1), and ciprofloxacin (CIP), as well as their impact on the removal of ARGs during sewage sludge composting. Our results demonstrated that composting achieved average removal efficiencies of 89.37 %, 72.63 %, and 82.98 % for OTC, CIP, and SM1, respectively. Metagenomic sequencing revealed that antibiotic residues significantly promoted the elimination of ARGs by 26.05–40.81 %. In contrast, the CK treatment resulted in a notable increase in tetracycline-resistant genes, particularly ade F, tet X, and sox R, compared to the levels reduced under antibiotic-induced selective pressure. Redundancy analysis (RDA) indicated that temperature, pH, C/N, CIP, and Proteobacteria, Tenericutes, and Chloroflexi were significant factors influencing the reduction of ARGs ( P  < 0.05). Network analysis further confirmed that Proteobacteria, particularly genera such as Pseudomonas and Pseudoxanthomonas , were predominantly associated with ARGs. These findings indicated that antibiotic residues can effectively promote the rebound of related ARGs, and offer valuable insights for the source control of ARGs.