Many bacteria cannot tolerate acidic environments, especially under anaerobic conditions. Bacteria are generally neutrophiles. They grow best at neutral pH close to 7.0. Acidophiles grow optimally at a pH near 3.0. Alkaliphiles are organisms that grow optimally between a pH of 8 and 10.5. Microorganisms grow best at their optimum growth pH.

Kefir bacteria and yeasts, like sourdough, are acid loving. Not sure of the pH, but it can etch enamel like lemon juice or vinegar, but I haven't had a problem. My teeth are less sensitive now, and they do not stain at all like they used to.