If I remember this study it required a formulated liquid for “feeding” the good bacteria that kept away the bad bacteria. Not sure what came of it.
Edit: not the same. Getting my studies mixed up. This is the one I was thinking of, it’s a mouthwash to get rid of destructive bacteria.
The one I’m thinking about was in trial in a bio engineering community somewhere in Latin America (easy way to get financing, get people to pay to be your guinea pig)
Found it!