Holographic Microrheology of Streptococcus mutans insoluble polysaccharides

Streptococcus mutans exude glucosyltransferases that polymerize environmental sugars, such as sucrose, into polysaccharides (glucans). These glucans, mainly insoluble glucans provide bulk and structural integrity to the dental biofilm matrix, and actively participate in the formation of a cariogenic dental biofilm. Although disrupting the glucans would provide a sure route to preventing tooth decay, comparatively little is known regarding the physical properties of biofilm matrix, including their viscoelastic properties. Objective: Measure the viscoelastic properties of S. mutans insoluble polysaccharides (INS) using holographic microrheology. Methods: We used three-dimensional holographic particle tracking to perform microrheological measurements of the INS extracted from 5 days-old S. mutans UA159 biofilms grown in the presence of 1% sucrose. The INS was extracted with 1N NaOH. Nanometer-resolution video-rate holographic tracking of embedded colloidal spheres was used to provide accurate measurements of the polysaccharides' complex viscoelastic moduli, including insights into these properties' heterogeneity. Results: Using precision three-dimensional data obtained from digital holographic microscopy, we were able to calculate the mean square displacement and thus infer the complex viscoelastic moduli to study important physical properties of S. mutans insoluble polysaccharides. In addition, the viscosity of INS decreases with increasing applied shearing frequencies, which implies that at a higher shearing frequency, the biofilm would become more viscous and easier to be disrupted. Conclusion: Holographic microrheology may be a rapid and accurate method for quantifying dental biofilms' micromechanical properties, which could be useful for developing and screening new therapeutic agents against dental caries. (National Science Foundation Grant #DMR-0606415)