Humans are known to acquire intestinal bacteria from the environment. As long as you keep a decent (as opposed to: overdone) hygiene, and you don’t use antibacterial soap everytime, and you don’t disinfect your surroundings with dettol or similar.
Babies do that, for example. Little children do that too. It’s one of the reasons they tend to put everything into their mouth.
Adults do it, too. As you may know, the bacteria you carry with you vary from person to person, but there are several regional similarities. If you emigrate to a different place, you’ll acquire the local bacteria. It may take some time, but you will acquire new species.
That is correct but no enough to replace the main bacterial species one time they are damaged. Changes in the microbiota are seen after changes in the alimentary regime, etc.
What science hasn’t proof is those changes are enough to modulate and reshape a damaged indigenous flora.