A messed up gut ecology has two major causes: poor diet and Antibiotics .
I believe milk kefir can colonize the gut, IF the bowels are free of pathogens. I was doing several high enemas a day for monthes on a juice fast, because I was fighting a severe parasite and candida overgrowth, and had to stop one day all of a sudden. The next day I was going twice a day to the loo. All I did to recolonize was some milk kefir.