Malolactic fermentation by Streptococcus mutans.

Streptococcus mutans and certain other oral lactic-acid bacteria were found to have the ability to carry out malolactic fermentation involving decarboxylation of L-malate to yield L-lactic acid and concomitant reduction in acidity. The activity was inducible by L-malate in S. mutans UA159 growing in suspensions or biofilms. The optimal pH for the fermentation was c. 4.0 for both suspensions and biofilms, although the pH optimum for malolactic enzyme in permeabilized cells of S. mutans UA159 was close to 5.5. Although malate did not serve as a catabolite for growth of S. mutans, it did serve to protect the organism against acid killing and to maintain ATP pool levels during starvation. Alkalinization associated with malolactic fermentation resulted in pH rise or increased need to add standardized HCl solution to maintain a set pH value in pH-stat experiments. The net conclusion is that malate has the potential to be effective for alkalinization of dental plaque, although the fermentation is sensitive to fluoride and triclosan, which are commonly added to oral care products.