Occurrence and Movement of Antibiotic Resistant Bacteria, in Tile-Drained Agricultural Fields Receiving Swine Manure
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 accelerate the transport of pathogen indicators such as enterococci as well as antibiotic-resistant bacteria. The objective of this study was to develop an understanding of the occurrence and transport of antibiotic-resistant enterococci in tile-drained chisel plow and no-till agricultural fields that have received multi-year application of liquid swine manure through injection. Enterococci resistance to tylosin in manure, soil and water samples was investigated phenotypically and compared with samples from control plots treated with urea and ammonium nitrate (UAN). The analysis found that 70% of the enterococci in manure samples were resistant to tylosin. Concentrations of enterococci in tile water were low, and only exceeded the geometric mean for recreational waters 9 times, with 33% of these exceedences occurring in tile flow from the control plots. The results of this study indicate that the occurrence of tylosin-resistant enterococci in tile water is low, found in only 16% of samples, in both control plots and plots receiving fall manure application.