by Workshop on Methods to Isolate Escherichia Coli O157:H7 and Other Verotoxigenic E. Coli from Foods (1991 Ottawa, Ont.) , Ont.) Workshop on Methods to Isolate Escherichia Coli O157:H7 and Other Verotoxigenic E. Coli from Foods (1991 : Ottawa , E. C. D. Todd , J. M. Mackenzie