A quantitative ultrastructural and chemical investigation of the accumulation of iodophilic polysaccharide in two cariogenic strains of Streptococcus mutans.

The amount of intracellular, iodophilic, glycogen-like polysaccharide (IPS) present in cells of two strains of Streptococcus mutans at various stages of growth in a chemically defined medium was determined by quantitative electron microscopy. The results obtained were then compared with the chemically determined, iodophilic polysaccharide content of cultures. The ultrastructural method used determined the fraction of area of central longitudinal sections of individual cells occupied by stained granules, and was therefore capable of determining amounts of polysaccharide in cells starved of glucose. Although the results of the two methods showed very good quantitative correlation, the ultrastructural method allowed study of glycogen synthesis on a cellular basis, and detected some heterogeneity in amounts of IPS stored by individual cells. The ultrastructural method also permits the detection of much smaller amounts of stored IPS than does the chemical method.