Fate and Transport of Tylosin and Macrolide-Resistance Genes Following Manure Applications in Tile-Drained Landscapes.

The use of antibiotics in swine production leads to antibiotic-resistance in gastrointestinal bacteria. Application of swine manure to drained agricultural fields introduces elevated levels of antibiotic-resistant bacteria and residual antibiotics.  The persistence and transport of these agent is governed by a variety of environmental, edaphic and management factors.  The persistence and transport of tylosin, Enterococcus (total and tylosin-resistant) and erm genes in manure, soil and tile-drainage were measured in chisel plow and no-till plots receiving liquid swine manure in alternate years. Manure used in the study was obtained from swine treated with tylosin. Each one-acre plot is drained separately and weekly water samples were collected directly from the tile line. Resistance to tylosin in manure, soil and tile drainage water was investigated using phenotypic based (membrane filtration) and genotypic based (qPCR) methods and compared with samples from control plots treated without manure. Tylosin was quantified using LC-MS/MS.  Enterococcus populations in the manure injection band immediately after application were elevated above background, but were well below the abundance of ermB or ermF (> 10⁸ gene copies/g soil).  However, over the next 24 months the erm genes declined in abundance to levels similar to those found in the non-manured soils (10³ to 3 x 10⁵ copies/g soil).  Concentrations of erm genes in tile drainage water were not different from those in drainage from the control plots.  Tylosin was present only in small concentrations.  The results suggest that antibiotic use in swine results in elevated levels of antibiotic resistant microorganisms in manure-treated soils, but that transport of microorganisms carrying resistance genes in tile drainage is not increased.