Candida is not microbial. Candida is a genus of fungus [yeast].
Gut fungus is in an entirely different class of treatment; antibiotics will not eradicate fungi, and fungus tends to grow tendrils and spores and generally work into every moist/dark crevice.
I understand all of this; what i meant to ask, i think, is: How do these detrimental gut flora get in to our systems, and how do we prevent that, or get rid of them? Is taking more bacteria helpful, in that it can out-compete the fungus? My experience with lacto and yeast is that both of those are well-equipped to outcompete nearly everything, especially if you give them lots of pure sugar.
Some are good (e.g. what you take probiotics to get more of), others are detrimental (e.g. h. Pylori, candida)