Sulfites are not sanitizers in the legal sense of the word. They do not kill anything. So why do we winemakers call them sanitizers? Because virtually all of the organisms that can hurt our wine require oxygen to grow, and sulfites strip the oxygen from the environment. Sulfites are reducing agents and act as follows (I will use K-meta as the example here, but just subistute Na for K for sodium metabisulfite):
K2S2O5 is K-meta crystals. When dissolved in water it becomes:
K2S2O5 + H2O --> 2(KHSO3) potassium bisulfite; which dissociates into:
K+ + H+ + SO3-2
This compound has about the same acidity as wine, so it fits right in. Now, here's the kicker:
2 x SO3-2 + O2 --> 2 x SO4-
What the sulfite has done is strip the dissolved oxygen out of the water, rendering the bad organisms unable to act. Without oxygen dissolved in the wine Acetobacter can do nothing. There could be millions of cells, but they would be inactive.
The inverse is yeast. Over-sulfiting a must before pitching the yeast will not kill the yeast, it will just prevent it from reproducing. If you want to prove this just take 750 ml of must, over-sulfite it, bottle it, put in some yeast, put a fermentation lock on it, and leave it for 5 years. Eventually it will ferment to dryness.