This is a draft schedule. Presentation dates, times and locations may be subject to change.

502
Dissipation of Antimicrobials and Resistance Genes in Compost Originating from Cattle Manure after Direct Oral Administration or Post-Excretion Fortification of Antimicrobials

Monday, July 10, 2017: 3:00 PM
316 (Baltimore Convention Center)
Shanwei Xu, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada
Inoka D. Amarakoon, Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada
Rahat Zaheer, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada
Srinivas Sura, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
Tim Reuter, Alberta Agriculture and Forestry, Lethbridge, AB, Canada
Francis Zvomuya, Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada
Allan J. Cessna, Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, Saskatoon, SK, Canada
Francis J. Larney, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada
Tim A. McAllister, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada
Our study compared the dissipation of antimicrobials and resistance genes (ARG) during composting of cattle manure fortified with antimicrobials versus manure from cattle administered the same antimicrobials in feed. Manure was collected from cattle fed diets containing (kg-1 dry feed): (1) 44 mg chlortetracycline (CTC), (2) a mixture of 44 mg each of chlortetracycline and sulfamethazine (CTCSMZ), (3) 11 mg tylosin (TYL) or (4) Control, no antimicrobials. Fortified treatments were generated by adding antimicrobials to control manure. All manures were composted for 30 d with a single mixing after 16 d. Quantitative PCR (qPCR) measured the concentration of 16S rDNA and genes associated with tetracycline (tet), erythromycin (erm), and sulfamethazine (sul) resistance. Over 95% of antimicrobials dissipated over 30 d of composting, but CTC and SMZ remained higher in fed than fortified treatments, with a reverse trend observed for tylosin. Copy numbers of 16S rDNA decreased (P < 0.05) over 30 d, but were not altered by the presence of antimcrobials. Levels of all ARG except tet(L) decreased by 0.1-1.6 log10 copies g dry matter-1 in the first compost cycle, but some genes [tet(B), tet(L), erm(F), and erm(X)] increased (P < 0.05) by 1.0-3.1 log10 copies g dry matter-1 in the second. This pattern aligned with the positive correlation of these ARG with residue concentrations in the first cycle and the negative correlation in the second. During 30 d of composting, levels of tet(M) and tet(W) in CTC, erm(A), erm(B) and erm(X) in TYL, and sul(1) in CTCSMZ remained higher (P < 0.05) in fed than fortified treatments. Our results suggest that dissipation of ARG during composting of manure fortified with antimicrobials differs from manure generated by cattle that are administered antimicrobials in feed and does not always align with the dissipation of antimicrobial residues.