There are tons of bacteria that are either neutral, good for you, or that you even *need". You just only hear about the ones that are bad for us, because they are comparitively rare.
I was referring more to enhancing nominal abilities, something that will positively change our body, maybe make it stronger, more resistivity, maybe act with our T cells to clean bad bacteria in gut that may cause depression ...
Instead process is always painfully slow, evolution over millions of years, just to get one positive trait.