There are many species of bacteria that live in the intestines of mammals. You're likely thinking of a specific group called gut microbiota, which are the trillions of bacteria that live in the digestive tract of mammals.

To give you a specific example, Escherichia coli (E. coli) is a very common and well-known bacterium that lives in the intestines of humans and many other mammals. However, it's important to remember that most bacteria in our gut are beneficial, playing a key role in digestion and immune function.

If you're interested in a specific type of gut bacteria, please provide more information and I'd be happy to help!