Bacterial Resistance to Tetracyclines In Soils Following Swine Effluent Application.

The widespread use of veterinary antibiotics could potentially lead to persistence of antibiotic resistant bacteria in the environment, and consequently pose a significant risk to human health as well as animal’s well-being. Tetracyclines, including chlortetracycline and oxytetracycline are one of the most broadly used classes of antibiotics in swine production. The main objective of the present study is to determine presence of chlortetracycline and tetracycline resistant bacteria in soils following over 15 year of annual swine effluent application. These soils were under continuous corn (Zea mays L.) cultivation since 1995 and were applied with swine effluent using center-pivot sprinkler system at rates of 62, 186, and 558 m³ effluent ha^-1. Thirty-six soils collected at depths up to 45 cm were analyzed for chlortetracycline concentration by high performance liquid chromatography with solid-phase extraction clean up. Soil bacterial community was assessed by culture-based method using tryptone soy agar plates. Antibiotic resistance of soil bacterial isolates was evaluated using the microbroth dilution method. Chlortetracycline was detected in soils at all three application rates even after 5 months of animal wastes application. Concentrations of chlortetracycline ranged from 0.02–0.26 mg kg^-1 soil with higher concentrations detected in the surface 15 cm of soil. Resistance and the degree of resistance to tetracycline among bacterial isolates will be discussed.  The obtained results are critical in developing regulations to guide animal waste management to protect public health as well as animal industry for sustainable production.