But… to be honest, I don’t like very much the expression “friendly bacteria” as used in your title…

I think that expressions such as “friendly bacteria”, “good bacteria” and the like, are overused in headlines — the implicit message is “you know, most bacteria are really bad guys but, hey, these ones are *friendly*!” (or “good” or whatever).

Only very few of the myriad bacteria on the planet are actually “bad guys” (that is, pathogens), so I think we all (including myself) should try to avoid that kind of underlying message.

Just my two cents…