Do you know some beneficial candida strains ??
I don't know about any.
That topic about no colonization is true. There isn't any evidence that current probiotics in any form can colonize the gut permanently. Another thing is the primary and dominant species aren't present in current probiotics as the other poster said. Probiotics, including Kefir, can only do temporary benefits to the gut. The only way so far to reach colonization is from human indigenous feces.
Jorge.