Effects of the ergot alkaloids dihydroergotamine, ergonovine, and ergotamine on growth of Escherichia coli O157:H7 in vitro.

ABSTRACT

A series of experiments were conducted to evaluate the effects of ergot alkaloids (dihydroergotamine, ergonovine, and ergotamine) on E. coli O157H7 in both pure and mixed ruminal fluid culture. Alkaloids were added to solutions of E. coli O157H7 strains 933 (pure and ruminal cultures) and 6058 (ruminal culture only), and growth rates and colony-forming units (CFU) of E. coli O157H7 were measured. Two mixtures of all three alkaloids at either 2 or 500 microM for each alkaloid decreased (p < 0.001) the growth rate of E. coli O157H7 in pure culture compared to the individual alkaloids. Dihydroergotamine tended (p = 0.07) to reduce growth rate of E. coli O157H7 in pure culture compared with ergonovine or ergotamine alone. Increased concentrations of dihydroergotamine and ergotamine decreased (p < 0.003) growth rate of E. coli O157H7 but increasing concentrations of ergonovine did not influence (p > 0.10) E. coli O157H7 growth rate. Similar to results in pure culture, a mixture of all three alkaloids at various concentrations for each alkaloid decreased (p < 0.001) the CFU of E. coli O157H7 strain 6058 in mixed ruminal culture compared to the individual ergot alkaloids. Dihydroergotamine decreased (p = 0.04) CFU of E. coli O157H7 strain 6058 when compared to ergonovine but CFU were similar (p > 0.10) between dihydroergotamine and ergotamine. Ruminal and (or) intestinal populations of E. coli O157H7 may be influenced in livestock consuming endophyte-infected tall fescue, and these alterations could be due to the presence of ergot alkaloids in fescue plants.