Synthesis of extracellular dextran by cariogenic bacteria and its presence in human dental plaque

Abstract

The extracellular polysaccharide synthesized primarily from sucrose by certain human and rodent cariogenic bacteria has been found to be a dextran-like polymer. Maximum quantities of this polysaccharide were synthesized in 10% sucrose broth, and the presence of free glucose or fructose did not markedly repress synthesis of dextran from sucrose. The dextrans synthesized by rat, hamster, and human cariogenic streptococci, and by a cariogenic strain of Lactobacillus acidophilus proved immunologically similar. The extracellular dextran was found to be relatively resistant to attack by mixed oral bacterial growth; to form insoluble precipitates with serum, clarified saliva, and various protein solutions; and to adhere to powdered hydroxyapatite. Samples of pooled human dental plaque were found to contain a constituent which was immunologically similar to dextran, and which comprised almost 2% of its dry weight. It is proposed that dextran synthesis by cariogenic but not non-cariogenic bacteria, enables these organisms to form dental plaque which is required for the production of dental caries.