Microbial aspects of frequent intake of products with high sugar concentrations

The Vipeholm Study showed that a frequent intake of products with high sugar concentrations increases caries activity. This effect of sugar was explained by the acid production of bacteria on the teeth. In the following 40 yr many microbial characteristics have been described, which are important in the pathogenesis of dental caries. This contribution focuses on one characteristic of the cariogenic bacteria; their acidurance. Compared to other oral bacteria the cariogenic lactobacilli and mutans streptococci have enzymes with greater resistance to acid, and greater capacities of the cells to extrude protons from the cytoplasm. The most important enzyme for the extrusion of protons is a membrane-bound proton-translocating ATPase. This enzyme is found in higher amounts and is working at lower pH in the cariogenic bacteria. Another important characteristic of the cariogenic bacteria is their production of lactic acid when they are exposed to high concentrations of sugar. Lactic acid has a pK of 3.8, while other carboxylic acids have a pK of 4.8. The bacterial cell membrane is permeable to undissociated carboxylic acids. These undissociated acids act as carriers to bring protons back into the cytoplasm. Bacteria with lactic acid as fermentation product have therefore the possibility to grow and produce acids at one pH unit lower than bacteria with, for example, acetic, propionic, or butyric acid as fermentation product.