In-feed antibiotic use changed the behaviors of oxytetracycline, sulfamerazine, and ciprofloxacin and related antibiotic resistance genes during swine manure composting

The dynamics of oxytetracycline (OTC), sulfamerazine (SM1), ciprofloxacin (CIP) and related antibiotic resistance genes (ARGs) during swine manure composting were compared between manure collected from swine fed a diet containing these three antibiotics (TD) and manure directly spiked with these drugs (TS). The composting removal efficiency of OTC (94.9 %) and CIP (87.8 %) in the TD treatment was significantly higher than that of OTC (83.8 %, P < 0.01) and CIP (83.9 %, P < 0.05) in the TS treatment, while SM1 exhibited no significant difference (P > 0.05) between the two treatments. Composting effectively reduced the majority of ARGs in both TD and TS types of manure, especially tetracycline resistance genes (TRGs). Compared with the TS treatment, the abundance of some ARGs, such as tetG, qepA, sul1 and sul2, increased dramatically up to 309-fold in the TD treatment. The microbial composition of the composting system changed significantly during composting due to antibiotic feeding. Redundancy analysis suggested that the abundance of ARGs had a considerable impact on alterations in the physicochemical parameters (C/N, pH and temperature) and bacterial communities (Actinobacteria, Proteobacteria and Firmicutes) during the composting of swine manure.