An electron microscope investigation of bacterial polysaccharide synthesis in human dental plaque

Abstract

The in vivo synthesis of both intracellular and extracellular polysaccharides by bacteria in dental plaque from a variety of dietary sugars has been examined by electron microscopy and the amounts scored by visual assessment of the sections and photo micrographs. Fine particulate granules which formed extracellular polysaccharide on contact with sucrose were found associated with the periphery of the bacterial cell. It was suggested that this particulate material could be the precursor of dextran or levan. The exposure of plaque in vivo to different sugars clearly indicated that sucrose and glucose are rapidly incorporated into intracellular polysaccharide whereas maltose, fructose, lactose and sorbitol are utilized slowly or not at all. The synthesis of extracellular polysaccharide was only accomplished in quantity from sucrose and to a smaller degree from maltose. Studying the catabolism of the polysaccharides synthesized from sucrose it was shown that even after 30 min the amounts of both intracellular and extracellular polysaccharides exceeded the amounts originally in the plaque before exposure to sucrose. It was observed that occasionally the extracellular polysaccharide was concentrated in localized areas within the plaque. As it was shown that the polysaccharides were retained for periods exceeding 30 min it was speculated this extracellular polysaccharide may restrict locally the diffusion of acid produced from intracellular polysaccharides.