Well, bacteria and the human host in general, actually. Clicking this link will lead you to a remarkable broadcast about the National Institutes of Health’s Human Biome Project.
The Human Biome Project is a marvelous international endeavor to learn everything that can be known (certainly at least much more than we know now) about the bugs that live in, on and all around us. The radio broadcast is from a regular BBC radio show, entitled Frontiers. So not only do you get to learn a whole lot about bugs and why they are so important to us, but you also get to listen to one of those nice cultured BBC voices that make everything seem alright.
Just remember two things: not all probiotic formulations are the same. Vidazorb® is the most tested and reliable product on the market. And the other thing to remember is You Are What You Absorb!