There's some info about Threelac on this website, also some pretty incredible testimonials.
They say the 3 spore-forming strands of bacteria 'eat' the yeast in your gut. Most people take Threelac long-term since the bacteria strands are transient (can't reside permanently). Threelac is meant to be unique because of its 'micro encapsulation' that helps it survive the stomach acid.
http://www.candidafree.net/index.htm