Streptococcus Mutans Intra-Species Impact on Oral Biofilms and Dental Caries
Objectives: The presence of multiple Streptococcus mutans, a key cariogenic organism, has been associated with increased dental caries scores in children. The purpose of this study was to compare how the presence of single and multiple S. mutans impact virulence properties in-vitro and in-vivo.
Methods: Two clinical S. mutans from a caries active child were selected from a large-scale epidemiological study. These two strain types (SmG09, SmG18) were the two most prevalent strain types in a high-caries population. Overnight biofilms (16 hrs) were generated in Todd Hewitt Broth with 1% sucrose using equal volumes of S. mutans grown individually or as a mix. S. mutans UA159 was used as a control. Biofilm assays were performed in triplicate to assess biofilm mass and pH with crystal violet and pHrodo dextran conjugate, respectively. Subsequently, strains were cloned with fluorescence proteins and antibiotic resistance cassettes for differential plating and confocal microscopy. Drosophila melanogaster was used as an initial in-vivo colonization model. Student’s T-test was used to determine significance.
Results: In this study, the mean biofilm pH was significantly lower in mixed biofilms (p=0.002) despite no changes in overall biofilm biomass. Pre- and post- biofilm setup cell counts were not significantly different between single and mixed biofilms. A significant increase of G09 biofilm height (p=0.01) was observed by confocal analysis. Bacterial spatial arrangements were visually distinct between single and mixed biofilms. Colonization in D. melanogaster exhibited greater colonization of SmG09 in flies colonized with mix over single.
Conclusions: The presence of multiple S. mutans strains resulted in significantly lower biofilm pH and greater overall colonization in-vivo indicating increased cariogenic potential. Changes in spatial orientation of biofilms could contribute to increased colonization through increase biofilm surface area for attachment of other oral microbial species. Future study with the rat caries model will be used to further determine cariogenicity in-vivo.