Those are supposed to be some of the good ones. I've read that there are hundreds of good ones and that getting a handle on just what they all do will be quite a task. Maybe it's enough to know that replenishing the good ones helps to crowd out the bad ones.
Do you happen to know if yogurt contains a particular strain of gut bugs, or is it a blend? I know you can buy pro-biotic capsules. I wonder if those have a select blend of the good ones.