Extracellular polysaccharide synthesized by the oral bacterium Streptococcus mutans of serotype a to e in vitro.

Extracellular polysaccharide (EPS) synthesized in vitro by Streptococcus mutans belonging to serotypes a, b, c, d and e was shown to consist mainly of glucan. Only strains of type b and e regularly produced substantial amounts of fructan, too. Strains of type d synthesized significantly higher quantities of glucan than strains of the other types per gram of bacterial mass. The percentage of insoluble glucan was lowest in samples from strains of type a and c, and highest in samples from strains of type d. In contrast to the insoluble glucan, the linkage pattern of the soluble glucan of the five types showed only small differences. The percentage of alpha-1,3-linked glucose units was highest in the insoluble glucan from strains of type d and e, and lowest in glucan from type c. The differences were significant. Incubation of Strep. mutans under various culture conditions showed that the quantities and composition of EPS formed depend on the culture condition used. The effect of culture conditions, however, was similar for all strains. Therefore the differences found with respect to the quantities and composition of EPS synthesized in vitro by Strep. mutans of different types are apparently type-dependent.