|Chee Sanford, Joanne|
Submitted to: Animal Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2006
Publication Date: 11/1/2006
Citation: Mackie, R.I., Koike, S., Krapac, I.G., Chee Sanford, J.C., Maxwell, S., Aminov, R.I. 2006. Tetracycline residues and tetracycline resitance genes in groundwater impacted by swine production facilities. Animal Biotechnology. 17:157-176. Interpretive Summary: he environmental effects of contamination from swine waste was investigated in groundwater underlying two farms, where routine application of manure to surrounding agricultural fields occurs. Tetracyclines, commonly used in animal production industries, and antibiotic resistance genes were used as chemical indicators of contamination, and serve as model markers to track the persistence and mobility of compounds input into the environment. These markers are significant due implications of increased antibiotic resistances emerging in municipal systems, and also provides suitable targets to track in the environment to examine the impact of agricultural inputs into soil and water systems. The results demonstrated four common tetracycline resistance genes persist but levels varied over time, likely dependent on farm management practices and soil and climate conditions during the study period. The significance of the study shows a chronic impact on the environment in terms of presence of genes and chemicals, and leads to further hypotheses on the long term impact of the continuing practice of manure application to soil and the consequent effects on soil microbial populations involved with important biogeochemical cycles.
Technical Abstract: Antibiotics are used at therapeutic levels to treat disease; at slightly lower levels as prophylactics; and at low, subtherapeutic levels for growth promotion and improvement of feed efficiency. Over 88% of swine producers in the United States gave antimicrobials to grower/finisher pigs in feed as a growth promoter in 2000. It is estimated that ca. 75% of antibiotics are not absorbed bya nimals and are excreted in urine and feces. The extensive use of antibiotics in swine production has resulted in antibiotic resistance in many intestinal bacteria, which are also excreted in swine feces, resulting in dissemination of resistance genes into the environment. To assess the impact of manure management on groundwater quality, groundwater samples have been collected near two swine confinement facilities that use lagoons for maure storage and treatment. Several key contaminant indicators-including inorganic ions, antibiotics, and antibiotic genes- were analyzed in groundwater collected from the monitoring wells. Chloride, ammonium, potassium, and sodium were predominant inorganic constituents in the manure samples and served as indicators of groundwater contamination. Based on these analyses, shallow grounwater has been impacted by lagoon seepage at both sites. Liquid chromatography-mass spectroscopy (LC-MS) was used to measure the dissolved concentrations of tetracycline, chlortetracycline, and oxytetracycline in groundwater and maure. Although tetracyclines were regularly used at both facilities, they were infrequently detected in manure samples and then at relatively trace concentrations. Concentrations of all tetracyclines and their breakdown products in the groundwater sampled were generally less than 0.5 µg/L. Bacterial tetracycline resistance genes served as distinct genotypic markers to indicate the dissemination and mobility of antibiotic resistance genes that originated from the lagoons. Applying PCR to genomic DNA extracted from the lagoon and groundwater samples, four commonly occurring tetracycline (tet) resistance genes - tet(M), tet(O), tet(Q), and tet(W)- were detected. The detection frequency of tet genes was much higher in wells located closer to and down-gradient from the lagoons than in wells more distant from the lagoons. These results suggested that in the grounwater underlying both facilities tetracycline resistance genes exist and are somwhat persistent, but that the distribution and potentially the flux for each tet gene varied throughout the study period.