Microrheological measurements of polysaccharides from Streptococcus mutans biofilms

Polysaccharides from Streptococcus mutans are one of the extracellular matrix' main components in dental biofilms, providing them with bulk and structural integrity. The insoluble-polysaccharides are also responsible for the adherence of S. mutans and other bacteria to the tooth surface, resulting in the establishment of a cariogenic dental biofilm. The presence of this biofilm, together with specific factors, is implicated in dental caries. Although disrupting the polysaccharide-pellicle would greatly reduce the incidence of caries, comparatively little is know regarding the physical properties of these biofilms. Objective: Measure the viscoelastic properties of soluble- and insoluble-polysaccharides from S. mutans biofilms by holographic microrheology. Methods: S. mutans UA159 (ATCC700610) polysaccharides samples were extracted from 5 days-old biofilms formed on glass slides in 10%-w/v sucrose. Water-soluble-polysaccharides were extracted with MilliQ water at room temperature. Insoluble-polysaccharides were extracted with 1N-NaOH at 37º C. The samples were neutralized to pH-7.0±0.5 and precipitated with cold ethanol (75%-v/v) overnight. The samples were dissolved in water(water-soluble) or 1N-NaOH(insoluble) to form gels used in the microrheological measurements, using three-dimensional holographic particle tracking. Nanometer-resolution video-rate holographic tracking of embedded colloidal spheres provides accurate measurements of the gel's complex-viscoelastic-moduli, including insights into these properties' heterogeneity. Results: The results suggest that water-soluble- and insoluble-polysaccharides have complementary roles in establishing the biofilms' mechanical and biological properties in vitro. The dynamic viscosity of Insoluble falls off with frequency, a signature that the gel is shear thinning. In the Water-soluble fraction, the dynamic viscosity is independent of the frequency. The Insoluble-type appears better suited to play the role of the mechanical scaffold within which the biofilms' bacteria colonies establish their ecosystem. Conclusion: Holographic microrheology applied to biofilms' polysaccharides shows promise to high-throughput combinatorial screening of candidate therapeutic or remedial agents against dental caries, offering direct insight into these agents' influence on the biofilms' physical properties. (NSF#DMR-0606415)