Characterization of escherichia coli O157 :H7 from downer and healthy dairy cattle in the upper Midwest region of the United States - Benson, A. K.; Buege, D. R.; Byrne, C. M.; Call, J. E.; Erol, I.; Fedorka-Cray, P. J.; Hiemke, C. J.; Kaspar, C. W.; Luchansky, J. B.; Wallace, F. M.