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[Retrograde]

12. Every human being on the planet has a gut full of E.coli

So do the rest of the mammals. The E. coli outbreaks that make the news are the result of poor sanitation - food preparers not washing their hands after defecation, raw feces being used as fertilizer, insufficiently clean produce, cross-contamination in processing plants.

E. coli is used for a lot of bacteriological research because it's common and easy to grow. For more than you probably care to know about the critters, check out Zimmer's book Microcosm: E. coli and the New Science of Life.