How bacteria are beneficial to animals?

Let's just put it this way, animals can't live without bacteria. I know that sounds crazy, but there are different kinds of bacteria. The kind that you and I think about a lot are hetatroph bacteria. They cause us to get sick. Autotroph bacteria on the other hand live in you and me inside our intestines. They also live in animals. If we and they didn't have them, we'd die. Hope this helps!