Escherichia coli, or E. coli, are a diverse group of bacteria. They typically thrive within the intestines of healthy animals. And, most of the time, they're perfectly harmless.

A few strains, such as E. coli O157:H7 — which commonly behind outbreaks in Canada and U.S. — have been identified as dangerous to people. Photo by Manjurul/iStock/Getty Images ...