if you drank the kefir, and\or took the *right* probiotics long enough - real, home made, raw milk kefir being the most beneficial as it contains beneficial yeasts, bacteria, etc... (I think of all the probiotics I have tried LB17 is perhaps the best) your intestinal tract was given time to repair - the beneficial microflora contributing greatly to this repair by cleaning out the sludge, debris, and eliminating toxins... then the beneficial microflora would begin, AFTER that has been accomplished, to colonize by laydown their own substrate against the intestinal walls... as the pH changes throughout the length of the intestine, each beneficial strain would eventually find its correct niche and place and colonize.
Due to the harsh environment though, it is important to continue to eat cultured\fermented foods as ALL people did almost daily before the advent of refrigeration...
This is also assuming that you have\had made great efforts to eat correctly and balance the weak acids with alkaline mineral intake in order to increase the buffering capacity of the body's fluids.
Once you have done that... the likely hood that established colonies would stick around (pun intended) for a longer period of time, goes up exponentially.
One piece of terrible junk food, especially the foods that are laden with artificial or refined ingredients, has the potential to change bacterial expression and reduce the population of the colonies.
The ideas presented here that these bacteria do not colonize has more to do with the way things *are* (damaged digestive tracts from mouth to anus, poor polluted environments, food, air, and water - along with the chemicals such as pharmaceuticals and OTCs, that people ingest), than the way they have been in the past, or the way that they should be.