Inhibitory effect of sorbitol on sugar metabolism of Streptococcus mutans in vitro and on acid production in dental plaque in vivo

This study was conducted to find out whether sorbitol inhibits the sugar me tabolism of Streptococcus mutans in vitro and the acid production in dental plaque in who. S. mutans NCIB 11723 was anaerobically grown in sorbitol-co ntaining medium. The rate of acid production from sugars was estimated with a pH stat. The rate of acid production from glucose or sucrose was not cha nged at various concentrations of oxygen. By the addition of sorbitol to su gar, however, the acid production was decreased with increasing levels of o xygen. Intracellular NADH/NAD(+) ratio and (dihydroxyacetone-phosphate+glyc eraldehyde-phosphate)/3-phosphoglycerate ratio were high whenever the acid production was inhibited by sorbitol. Sorbitol also inhibited the acid prod uction in dental plaque in vivo. These results suggest that the increased N ADH/NAD(+) ratio during sorbitol metabolism through the inactivation of pyr uvate formate-lyase by oxygen inhibited glyceraldehyde-phosphate dehydrogen ase and then the acid production of S. mutans and the one in dental plaque.