Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/27/2005
Publication Date: 12/1/2005
Citation: Wells, J.E., Berry, E.D., Varel, V.H. 2005. Effects of common forage phenolic acids on Escherichia coli O157:H7 viability in bovine feces. Applied and Environmental Microbiology. 71(12)7974-7979. Interpretive Summary: Persistence of Escherichia coli O157:H7 in animal production systems is a concern for U.S. agriculture. The E. coli O157:H7 survivability in beef cattle feces differed with type of diet, and with the hay diet studied, survivability differed with time on diet. Inoculated E. coli O157:H7 survived less than 30 days in feces from animals fed corn and less than 45 days in feces from animals fed corn silage. When cattle were fed bromegrass hay for less than one month, the E. coli O157:H7 survival was less than 30 days. However, the survivability of E. coli O157:H7 was much longer (>90 days) in the feces of animals fed the hay diet for more than one month. Since forages contain phenolic acids, and these compounds are known antimicrobials and are metabolized in the rumen of forage-fed animals, we expected that these compounds would affect E. coli O157:H7 survivability in the feces of animals not fully adapted to the hay diet. Plant phenolic acids were added to feces from beef cattle fed diets of corn silage or corn, and the E. coli O157:H7 died rapidly (typically less than four days). This study has identified naturally occurring compounds that might be useful to control E. coli O157:H7 transmission from production systems to the environment.
Technical Abstract: The survival of Escherichia coli O157:H7 inoculated into feces differed from cattle fed hay or corn silage, and in subsequent experiments, grass phenolic acids affected viability. When animals were on bromegrass hay less than one month, viable E. coli O157:H7 decreased rapidly in feces and no cells were recovered after 30 days. However, in feces collected from animals that had been consuming the hay diet for two to four months, E. coli O157:H7 cells decreased slowly and were recovered for as long as 120 days. In contrast, viable E. coli O157:H7 cells in feces from animals fed corn silage were detected for about 45 days and did not differ with time on diet. Plant phenolic acids decreased viability of E. coli O157:H7 in feces from animals fed corn silage or corn. When 0.5% trans-cinnamic acid or 0.5% para-coumaric acid was added to feces from silage-fed animals, E. coli O157:H7 death rate was increased significantly (17-fold and 23-fold, respectively) compared to no addition. In feces from corn-fed animals, E. coli O157:H7 death rates were increased significantly for 0.1% and 0.5% trans-cinnamic acid (7- and 13-fold), 0.1% and 0.5% p-coumaric acid (3- and 8-fold), and 0.5% ferulic acid (3-fold). Fecal pH (5.3 to 6.3) had a slight effect on the death rate of E. coli O157:H7, but a lower fecal pH significantly enhanced effects of phenolic acids to kill E. coli O157:H7. These data suggest that phenolic acids common to forage plants can decrease viable counts of E. coli O157:H7 in feces.