Enterohemorrhagic Escherichia coli serotype O157:H7 is a pathotype of diarrheagenic E. coli that produces one or more Shiga toxins, forms a characteristic histopathology described as attaching and effacing lesions, and possesses the large virulence plasmid pO157. The bacterium is recognized worldwide, especially in developed countries, as an emerging food-borne bacterial pathogen, which causes disease in humans and in some animals. Healthy cattle are the principal and natural reservoir of E. coli O157:H7, and most disease outbreaks are, therefore, due to consumption of fecally contaminated bovine foods or dairy products. In this review, we provide a general overview of E. coli O157:H7 infection, especially focusing on the bacterial characteristics rather than on the host responses during infection.