Morphological Characteristics of and Exopolysaccharide Effect in three Single-Species Biofilms

Objective: To observe the structures of monospecies biofilms of Streptococcus mutans, Actinomyces viscosus, and S. sobrinus grown for 24 hours, and to analyze the distribution and effect of exopolysaccharide in them. Methods: 1. The three bacteria were grown in TS broth and formed monobacterial biofilms on nonpellicle glass sheets soaked in the broth. The structures of these biofilms and the distribution of exopolysaccharide were visualized by confocal laser scanning microscopy after the biofilms were stained with the fluorescent agents BODIPY™ and Calcofluor™. 2. The three strains were grown in culture solution with 0.25%, 0.5%, 1.0%, or 1.5% sucrose, either in rocking or stationary culture, the total amounts of polysaccharide produced by the bacteria were determined by the anthrone method. Results: 1. The single-species biofilms characterized by net-like structures, crossed by channels. 2.More soluble and insoluble polysaccharide was produced by S. mutans in the biofilm than in the planktonic phase at every sucrose concentration (n=6/gp,P<0.05). Actinomyces viscosus and S. sobrinus produced more insoluble polysaccharide in the surface phase than in the planktonic phase (n=6/gp, P<0.05). Conclusions: The ability of S. mutans to synthesize polysaccharide was enhanced in the adherent phase, which may clarify why S. mutans in biofilms are highly cariogenic.