Dissipation of antimicrobial resistance genes in compost originating from cattle manure after direct oral administration or post-excretion fortification of antimicrobials
Xu, S., Amarakoon, I.D., Zaheer, R., Smith, A., Sura, S., Wang, G., Reuter, T., Zvomuya, F., Cessna, A.J., Larney, F.J., McAllister, T.A. (2018). Dissipation of antimicrobial resistance genes in compost originating from cattle manure after direct oral administration or post-excretion fortification of antimicrobials. Journal of Environmental Science and Health, Part A: Toxic - Hazardous Substances & Environmental Engineering, [online] 53(4), 373-384. http://dx.doi.org/10.1080/10934529.2017.1404337
Plain language summary
In this study, we examined the presence of antimicrobial resistance genes during composting of cattle manure. We examined manure from cattle that was fortified with antibiotics versus manure from cattle that were given antimicrobials in their feed. Results showed that the depletion of antibiotic resistance genes during composting of manure fortified with antimicrobials differs from manure generated by cattle that are administered antimicrobials in feed.
Dissipation of antimicrobial resistance genes (ARG) during composting of cattle manure generated through fortification versus administration of antimicrobials in feed was compared. Manure was collected from cattle fed diets containing (kg−1) dry matter (DM): (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. Manures were composted for 30 d with a single mixing after 16 d to generate the second heating cycle. Quantitative PCR (qPCR) was used to measure 16S rDNA and tetracycline (tet), erythromycin (erm) and sulfamethazine (sul) genes. Temperature peaks ranged from 48 to 68°C across treatments in the first composting cycle, but except for the control, did not exceed 55°C in the second cycle. Copy numbers of 16S rDNA decreased (P < 0.05) during composting, but were not altered by antimcrobials. Except tet(L), all ARG decreased by 0.1–1.6 log10 g DM−1 in the first cycle, but some genes (tet[B], tet[L], erm[F], erm[X]) increased (P < 0.05) by 1.0–3.1 log10 g DM−1 in the second. During 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. The 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.