I don't see how a parasite could possibly feed on good bacterias. Even if it would, parasites can feed on mostly anything anyway, even on our blood. Also, we have trillions of bacterias in our guts, so introducing billions at a time is like a drop of water in an ocean.
I believe quite the opposite in fact, and I had only positive experience regarding probiotics for fighting parasites and candida. When I say positive experience, it is with homemade kefir or sauerkraut, not the useless and expensive probiotic pills.