Location: Agroecosystem Management Research
Title: Evaluation of a vegetative treatment system to reduce fecal microorganisms and antibiotic resistant bacteria in beef cattle feedlot runoff Authors
Submitted to: Microbial Ecology International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: June 10, 2012
Publication Date: August 19, 2012
Citation: Miller, D.N., Durso, L.M., Henry, C.G. 2012. Evaluation of a vegetative treatment system to reduce fecal microorganisms and antibiotic resistant bacteria in beef cattle feedlot runoff. Microbial Ecology International Symposium. Section PS22 Microbial Disease Ecology. Poster 391A. Interpretive Summary: Feedlot runoff often contains manure nutrients, fecal indicator microbes, pathogenic bacteria, and antibiotic-resistant bacteria. A vegetative treatment system consisting of bermed grass treatment areas can assimilate nutrients and serve as an area where pathogens and fecal indicator organisms quickly die off. At one vegetative treatment system in central Nebraska, fecal indicator microbes, pathogens, and antibiotic-resistant microbes were detected during several runoff applications over two years. Excess runoff that accumulated at the lower end of the treatment areas after a few hours still contained fecal indicator organisms, pathogens, and antibiotic resistant bacteria. When clean rainfall ran off the treatment areas, many microbes of concern (O157:H7 and cephalosporin resistant microbes) were not detected. Only tetracycline resistant microbes were detected. In soil samples the concentration of fecal indicator organisms decreased with depth, and numbers were no greater than in untreated berm soil samples. Based on these results, the vegetative treatment systems provide good control over time of fecal indicator organisms, pathogens, and antibiotic-resistant microorganisms.
Technical Abstract: Vegetative treatment systems designed to treat beef cattle feedlot runoff are an alternative to holding ponds and involve short-term runoff accumulation in basins and application to grass treatment areas. Field evaluations are needed to determine if pathogens, fecal indicators, and antibiotic resistant microorganisms are reduced during standard operation. Total coliforms, E. coli, Enterococcus, and STEC O157 were monitored using culture-based and molecular methods over two years in feedlot runoff and in treatment area soil samples collected to a 50 cm depth at a VTS site in central Nebraska, USA. Tetracycline- and cephalosporin-resistant bacteria were also enumerated in runoff events and from soil samples using selective media. Feedlot runoff was applied on six separate dates during the study period and soil cores (0 to 50 cm) were collected annually. Large variations (up to four orders of magnitude) in microbial runoff water quality parameters were observed between dates. Total coliforms, E coli, and Enterococcus in the feedlot runoff averaged 3.4 x 105, 2.2 x 105, and 3.3 x 104 per mL, respectively. STEC O157 was detected in 92.5% of the feedlot runoff and in 77.4% of the samples collected at the downslope end of the treatment areas where excess feedlot runoff accumulated. Tetracycline-resistant bacteria were detected in all feedlot runoff and in all samples where excess feedlot runoff accumulated. Cephalosporin-resistance was less pervasive and was present in 22.5% of the feedlot runoff and 10% of the downslope runoff samples. To investigate the persistence of fecal microbes after effluent application, runoff generated from direct rainfall precipitation on the treatment areas was tested and found to be negative for STEC O157 and cephalosporin-resistant microorganisms. However 70.8% of the rainfall runoff samples were positive for tetracycline-resistant microorganisms. Soil depth profile samples of total coliforms, E coli, and Enterococcus from four replicate treatment areas sampled in autumn showed distinct vertical profiles. The abundance of was highest (P < 0.05) at the surface for total coliforms and Enterococcus (4926 and 2062 per gram soil, respectively) and lowest in the deepest cores (103 and 530 per gram soil, respectively). E. coli abundance was low, decreasing with depth (19.5 to 0.3 per gram soil surface to bottom). Only a single surface soil sample tested positive for STEC O157; no other depths or other sites were positive for STEC O157. Similarly, no tetracycline or cephalosporin-resistant microorganisms were detected in any of the soil samples. There were no differences between indicator and pathogenic microbes in the soil profiles of treatment areas receiving feedlot runoff compared to the berm areas that received no feedlot runoff with the exception of higher coliform counts in the surface soils (0-5 cm and 5-10 cm) of the berm soil samples. Based upon the microbiological results, we conclude that vegetative treatment systems are a good tool to manage fecal microorganisms and antibiotic resistant microbes commonly found in beef cattle feedlot runoff.