The effect of anaerobic digestion (AD) and composting manure management strategies on antimicrobial resistance (AMR) was explored at the farm and bench-scale. At the farm-scale, a collaborative project investigated the fate of antibiotics and antimicrobial resistance genes (ARGs) during manure handling, treatment, and storage at 11 dairy farms. Results showed that antimicrobials were not consistently removed during manure treatment, with most samples below detection limit, yet, others showing concentrations up to 34,000 ng/g DW in the AD effluent, for example. Antimicrobials also did not degrade significantly during field-scale composting. The farm-scale results illuminated limitations of tracking antimicrobials in complex manure treatment systems with varying manure treatment practices, retention times, and heterogeneous manure substrates. At the bench-scale, triplicate reactors with tetracycline (TC) and sulfadimethoxine (SDM) additions of 1 and 10 mg/L were digested with dairy manure and inoculum for 44-days. The AD process degraded 85% of antimicrobials at the bench-scale. There was a 99% reduction of SDM during AD. The AD reactors with TC additions showed more variability in degradation products. The ARG analysis showed that TetM gene copies decreased during AD and correlated with declines in TC, however, reductions in SDM did not correlate with decreases in Sul1 gene copies. Overall, our results showed that dairy farm antibiotics usage varies significantly from farm to farm, with occasional short-term spikes in usage in response to the treatment of illness/infection outbreaks, and therefore, tracking these spikes through complex manure handling systems proved challenging. The settling, separation, and differing retention times of solids throughout manure handling processes also made whole-farm analyses challenging, as recovery rates in the extraction process for testing antimicrobials in the laboratory varied with solid-based and liquid-based manure samples.
Authors
Stephanie Langsing, University of Maryland, slansing@umd.edu
Schueler, Jenna (University of Maryland); Crossette, Emily (University of Michigan); Naas, Kayla (University of Buffalo); Hurst, Jerod (University of Buffalo); Oliver, Jason (Cornell University); Raskin, Lutgarde (University of Michigan); Wigginton, Krista (University of Michigan); Gooch, Curt, (Cornell University); Aga Diana (University of Buffalo)
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