Great point about gut bacteria. Aside from lettuce greens we may eat, the largest amount of Vitamin K we get comes from a variety of these intestinal bacteria, including E. Coli. Vitamin K is a very essential human need, and the main way most of us get it is apparently from this bacteria.
E. coli is definitely a love/hate relationship. They are essential to the lower colon, but anywhere else in the body they are a dangerous risk.
It remains one of the most diverse bacterial species: only 20% of the genome is common to all strains. To put this in perspective, humans and fruit flies share 60% of their genome.