Escherichia coli bacteria cause many illnesses of the gastrointestinal tract. Often, people come down with these diseases when they eat contaminated foods, especially ground beef or raw produce. Though E. coli infections are most common in less developed parts of the world, they are also a problem in the United States--contamination occurred in prepackaged cookie dough in 2009 and in spinach in 2006. But all E. coli are not harmful, as strains...