Bacteria in a person’s mouth convert glucose, fructose, and sucrose into acids through a process called glycolysis, which is the main energy generating pathway in all bacteria, including S. mutans. The monosaccharides glucose, galactose, and fructose can enter the glycolysis pathway at the points shown in the diagram (Figure 6). The dotted lines in the pathways indicate that there are additional intermediate steps. S. mutans is capable of metabolizing pyruvate (pyruvic acid) further to generate yet more energy and more acid byproducts. When excess sugars are available they favor the lactate dehydrogenase pathway to produce lactic acid; between meals, they utilize their energy reserves and produce formic and acetic acid instead.
Figure 6. Glycolytic pathway of Streptococcus mutans, from monosaccharides to acid.
Adapted from: Marsh PD, Lewis MAO, Rogers H, et al. Oral Microbiology. 6th ed. 2016; Edinburgh: Churchill Livingstone Elsevier.