@umbra21 - The problem is that the normal microflora in the human body has got there through generations of evolution, where we've grown to rely on each other in ways that we are still only just understanding.
Any attempts by scientists to interfere with that relationship can end up with the indigenous microflora being damaged, and the human host being harmed as well.
I mean, the bacteria in our mouths probably do something for us. If you introduce a bacteria that feeds on them, they might disappear altogether, which might have unintended consequences.
I think it's an interesting line of research, but I'm not going to purposefully infect myself with new bacteria any time soon.