Occurrence and movement of total and tylosin-resistant enterococci, erm genes and tylosin in tile-drained agricultural fields receiving swine manure application

The use of tylosin at subtherapeutic levels by the swine industry provides selective pressure for the development of antibiotic resistance in gastrointestinal bacteria. The land application of swine manure to drained agricultural fields might introduce elevated levels of total and tylosin-resistant enterococci, erm genes and tylosin. The goal of this study was to develop an understanding of the occurrence and transport of total and tylosin-resistant enterococci, erm genes and tylosin in tile-drained chisel plow and no-till agricultural fields that have received multi-year application of liquid swine manure through injection over two growing seasons. Resistance to tylosin in manure, soil and water samples was investigated at the field scale level using phenotypic based (membrane filtration) and genotypic based (qPCR) methods and compared with samples from control plots treated with urea and ammonium nitrate (UAN). Tylosin was quantified using LC-MS/MS. Plots in a corn-soybean rotation were identified for sampling from 2010-2012. Soil samples were collected from each manure plot, from both the direct area of injection and from the area between the manure bands and from control plots. Each one-acre plot is drained separately and tile water samples were collected directly from the discharge tile line weekly while the tiles were flowing. The results of this study suggest that tylosin usage has increased the short-term occurrence of total and tylosin-resistant enterococci, erm genes, and tylosin in soils, but has had minimal effect on tile drainage water quality under dryer than average condition