The bacterium Escherichia coli was previously considered a non-pathogenic microorganism, common in the gastrointestinal tract of both humans and animals. It is used as an indicator bacterium in routine examinations of water to detect fresh contamination with faeces.
Over the years, it has been shown that there are several different types of Escherichia coli, which can cause disease in humans, some of these can also be found in animals, but the animals are rarely sick.
Source: Public Health Agency