Purpose: The purpose of the study is to assess whether biological treatment of manure has an effect on the occurrence and fate of antibiotic residues, antibiotic resistance genes, and zoonotic pathogens.
Methods: Samples were taken from different stages of the biological treatment of swine manure on one pig farm, at six different time points with a two-week interval. The quantification of antibiotic residues (ceftiofur, colistin, doxycycline, oxytetracycline, sulfadiazine, trimethoprim and tylosin A) was performed with UHPLC-MS/MS. Tetracycline resistance genes (tet(B), tet(L), tet(M), tet(O), tet(Q) and tet(W)) were quantified using real-time PCR. The presence of zoonotic pathogens (Salmonella spp. and Campylobacter spp.) and Escherichia coli, as indicator bacterium, was assessed using culture techniques.
Results: Our results showed a reduction of sulfadiazine and doxycycline after biological treatment of manure. This treatment resulted in at least a 10‑fold reduction of the tetracycline resistance genes, with the exception of tet(L). Concerning the pathogens, our results show that Salmonella Typhimurium can be present in the different stages preceding the biological manure treatment, but it was never detected in the storage lagoon. The Campylobacter that was detected in the liquid fraction, only, and confirmed as Campylobacter coli. For E. coli, a reduction from 105 cfu/g to below the detection limit was observed during biological treatment of swine manure.
Significance: The data suggest that biological treatment of manure may be a tool to reduce the amount of antibiotic residues, tetracycline resistance genes, and zoonotic pathogens present in the manure.