Unfortunately probiotic organisms don’t have any effect on actual gut bacteria. There are upwards of 28 strains of lactobacillus and acidophilus which are what yogurt and kefir are made by. Then there are the leuconostoc bacteria that are responsible for sauerkraut and kimchi. You can easily consume a trillion live cultures of probiotics in a day and it will have no noticeable effect on your health. I think going to Mexico and drinking a glass of water would be more effective.
FWIW, I just looked at a bunch of papers published in the last few months that argue otherwise.
I’ll keep drinking the kefir. :-)