E. coli are a very common kind of prokaryote cell that lives mainly inside mammals and birds, including inside you. They can only live for a short time on their own, because they have evolved over time to live inside animals. E. coli live in your intestines, where they eat some of your food and break it down into smaller molecules that you can get into your blood. They can eat a lot of different kinds of food.
Babies are born without E. coli inside them, but they usually get some inside them before they are two days old, from the hands of people who hold them. E. coli cells are so simple that they can build all the parts of the cell out of just one kind of sugar molecule (glucose). Some kinds of E. coli bacteria have flagella, so they can swim around inside you, and others don’t.
Most kinds of E. coli bacteria don’t hurt you, and in fact you need them to help digest your food. These E. coli bacteria also kill off other germs that might hurt you, and some of them produce vitamins you need. You usually have millions of them inside your gut. But a few kinds of E. coli bacteria are poisonous, and occasionally people even die from eating the wrong kind of E. coli. You can avoid most bad E. coli infections by cooking meat well before eating it, and washing your hands with soap often when you are cutting up raw meat and after you go to the bathroom.