"The large number of beverages and soda fountain machines containing E. coli is still of considerable concern... and suggests that more pathogenic strains of bacteria could persist and thrive in soda fountain machines if introduced, " the authors wrote.

CNN: Soda fountains contained fecal bacteria, study found

Cholera outbreaks, such as the one that hit Peru and its neighbours in the early 1990s, tend to happen suddenly, as the formerly benign bacteria turn on their pathogenic apparatus when they hit the body.

ECONOMIST: The cholera genome

Many of the bacteria in question are genuinely mutualistic with their hosts, helping the process of digestion or warding off pathogenic bugs.

ECONOMIST: Inhuman genomes