I'd guess that the balance of bacteria depends more on whole-system factors, especially diet and personal chemistry/digestive-tract-structure. Unless a strain i

I'd guess that the balance of bacteria depends more on whole-system factors, especially diet and personal chemistry/digestive-tract-structure. Unless a strain is completely missing, adding a few more of one kind might be unlikely alone to change the equilibrium. Now, if you knocked out the old strains with antiobiotics, the repopulation might be more sensitive to the small amounts first reintroduced. These studies of a wasting disease in Africe offer more hints of the interplay of gut microbiome, diet, and antibiotics: http://www.nytimes.com/2013/01/31/health/antibiotics-can-save-lives-of-severely-malnourished-children-studies-find.html http://www.nytimes.com/2013/01/31/health/antibiotics-can-sav...