Author: Sheridan Kidd Haack, Research Hydrologist/Microbiologist, U.S. Geological Survey
There has been at least one thorough research review which showed no conclusive evidence that E. coli O157:H7 developed as a result of feeding grain to cattle. Further, E. coli O157:H7 has been found not only in cattle but also in a wide variety of other animals such as seagulls, deer, and others (it is unknown if the strains of E. coli O157:H7 from wildlife are capable of causing human illness as the strains from cattle are).
Additional reading:
D. Hancock and T. Besser. 2006. E. coli O157:H7 in hay- or grain-fed cattle. College of Veterinary Medicine, Washington State University. http://www.puyallup.wsu.edu/dairy/joeharrison/publications.asp