METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Efficacy of chlorate against E. coli O157:H7 and Salmonella Typhimurium in bovine feedlot soil mixture.
Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 14, 2007
Publication Date: July 8, 2007
Citation: Oliver, C.E., Magelky, B.K., Bauer, M.L., Caton, J.S., Hakk, H., Larsen, G.L., Anderson, R.C., Smith, D.J. 2007. Efficacy of chlorate against E. coli O157:H7 and Salmonella Typhimurium in bovine feedlot soil mixture. Meeting Abstract. American Society of Animal Science Meetings, July 8-12, 2007, San Antonio, TX.
Our aim was to determine if chlorate, temperature, or atmosphere affected pathogen viability in feedlot soil. Aliquots (1 g) of dried bovine feces/soil mixture (75:25 w:w) and 1 mL bovine urine were incubated in 10 or 20 mL glass serum vials with chlorate (0, 17, 33, or 67 ppm), at 6, 20, or 30°C, under aerobic or anaerobic conditions. Each vial was inoculated with 1 mL of a fresh bovine fecal supernatant mixed with overnight cultures of E. coli O157:H7 strain 933 (EC) and Salmonella enterica Typhimurium DT104 (ST) in an 8:1:1 ratio. Aerobic vials were weighed daily and evaporative loss replaced with distilled water. Anaerobic vials were capped with a butyl stopper and aluminum seal. Samples were collected on d 0, 0.5, 1, 3, 7, 14, 21, and 28; serially diluted in phosphate buffered saline; and plated on MacConkey and XLT-4 agars. Plates were incubated at 39°C for 24 h and pathogens were counted. A second study was performed using sterile feedlot soil and fecal supernatant, so that added EC and ST were the only live bacteria present in the cultures. In the first study, EC was not detected in any aerobic cultures by d 3 at 20°C and by d 1 at 30°C. At 6°C, EC was not detected at 67 ppm chlorate by d 21, but persisted through d 28 in the remaining cultures at log10 4 to 5.5 bacteria/mL culture. Aerobic cultures at all temperatures had no detectable ST by d 21 to 28. Pathogens in anaerobic cultures were detected in nearly all cultures at d 28, however, bacterial counts declined over time. In sterilized feedlot soil, results were similar. In both studies, there was no effect of chlorate on pathogen viability at the higher temperatures, but at 6°C there was an apparent chlorate dose-dependent decline in EC counts. Chlorate may be effective in preventing pathogen persistence in feedlot soils at ~6°C temperatures.