Q-306. Inhibitory Activity of Sainfoin (Onobrychis viciifolia), a Phytochemical Rich Forage and Pure Phenolic Compounds on Escherichia coli

N. C. Berard1, R. A. Holley1, K. H. Ominski1, T. A. McAllister2, K. M. Wittenberg1, D. O. Krause1;
1Univ. of Manitoba, Winnipeg, MB, CANADA, 2Agriculture and Agri-Food Canada, Lethbridge, AB, CANADA.

Background: It has been speculated that antibiotic use in agriculture may play a role in the development of antimicrobial resistance in pathogenic bacteria. We hypothesized that sainfoin (Onobrychis viciifolia), a tannin-containing forage, and plant derived phenolic compounds would reduce the number of Escherichia coli shed from cattle. Methods: Sainfoin and alfalfa (Medicago sativa) were made into either silage or hay. Sainfoin and alfalfa acetone extracts were prepared and minimum inhibitory concentrations (MIC) were determined against E. coli O157:H7 using a colorimetric microdilution assay. MICs were also determined for pure phenolic compounds (p-coumaric, cinnamic, and ferulic acid) against three different E. coli strains. In an in vitro study, fecal samples were collected from cattle fed alfalfa hay and inoculated with a ciprofloxacin-resistant strain of E. coli O157:H7 (E. coli Cipr). Ground sainfoin or pure p-coumaric acid were added at 0.5% (w/w) to the fecal samples and incubated at -20, 5, or 37°C for 14 d to evaluate the viability of E. coli Cipr. In an in vivo study, 40 steers were fed either sainfoin (silage or hay) or alfalfa (silage or hay) diets for 9 wks to determine the effect of sainfoin on fecal shedding of E. coli. Results: The MICs for the forage extracts were in the range of 25-40 mg/mL whereas the pure phenolic compounds had MICs of 1-4 mg/mL. In comparison, the MIC of ciprofloxacin was 0.05 µg/mL. In the in vitro study, E. coli Cipr declined significantly (P < 0.05) in the presence of coumaric acid at -20, 37, and 5°C but in the presence of ground sainfoin only at -20 and 37°C. At 5°C the death rates of E. coli Cipr were much lower than the other temperature regimens suggesting that a protective mechanism is occurring at this temperature. In the in vivo study, fecal E. coli shedding at the end of the trial was approximately one log less in the sainfoin compared to the alfalfa fed cattle. Conclusion: Tannin-containing forages and phenolic compounds may be useful in reducing the viability of E. coli but is not nearly as effective as first line gram-negative antimicrobials like ciprofloxacin.