ObjectiveTo observe the different abilities in synthesizing exopolysaccharides between biofilm cells of Streptococcus mutans (S. mutans) clinical isolate 593 and standard stain S. mutans ATCC 25175 (serotype c). MethodsS. mutans biofilm specimens were formed on the polystyrene plastic sheets for 3, 12 and 20 h. The exopolysaccharides was stained with fluorescein isothiocyanate-conjugated concanavalin A and were visualized by confocal laser scanning microscopy. The amounts of exopolysaccharides produced by adhesive S. mutans in 3-24 h were determined by the anthrone method. ResultsThe green fluorescence in strain 593 group was stronger and wider than that in the S. mutans ATCC 25175 group, with significant differences found for the amounts of water-soluble glucans during 3-20 h and water-insoluble glucans during 3-16 h (P<0.05). ConclusionThe synthesis of exopolysaccharides during formation of biofilm increases with time in both clinical and standard strains of S. mutans. However, the stronger synthesizing ability of strain 593 in the early biofilm formation stage(3-16 h) may be the reason for its higher cariogenic ability, indicating that the clinical isolates may be more sensitive in studying the mechanism of caries pathogenesis.