Mutans streptococci are able to grab any sugar that enters the mouth. They use the sugar to change the pH in the mouth. They then form acid on the teeth. It is this acid that causes teeth to decay. The lactobacilli are more able to survive in an acid environment.
Bacteria changes all foods into acid.
Sugars and starches are favorites of bacteria. Plaque is formed by bacteria, acid, food debris, and saliva. Plaque is a sticky substance that sticks to the teeth. Plaque is easily detected on the grooved chewing surfaces of the back molars, just above the gum line, and at the edges around fillings. When plaque is not removed from the teeth it becomes tartar.