Duplex RT-qPCR for Detection of S. mutans and S. sanguinis

Streptococcus mutans is the major microbial pathogen associated with dental caries. Streptococcus sanguinis is known to play an antagonistic role against the colonization of S. mutans in the oral cavity. Based on conventional culture methods, it has been suggested that the S. mutans/S. sanguinis ratio may serve as a caries risk indicator. Objectives: To detect and quantify S. mutans and S. sanguinis in the saliva of a mother-child cohort using duplex real-time quantitative PCR (qPCR) and to evaluate the association of S. mutans/S. sanguinis ratio and caries status. Methods: Twenty 2 to 8-year-old children (10 caries active vs. 10 caries free) and their mothers were included in this study. Stimulated whole salivary samples were collected, total bacterial genomic DNA was isolated, and a duplex real-time qPCR assay with species-specific primers and probes was performed. Results: Using fluorescent Taqman assay, S. mutans and S. sanguinis were detected in the saliva of 95% and 100% of the children, respectively. The children's caries severity was significantly correlated with that of their mothers (p = 0.02). The mean level of S. mutans was significantly higher in caries-active children than caries-free children (p = 0.015). There was a 10-fold increase in S. sanguinis level in caries-free children compared to caries-active children. The S. mutans/S. sanguinis ratio was marginally correlated with children's caries severity (p = 0.062). Conclusions: This study demonstrated significant correlations between caries severity and S. mutans colonzation in children. S. mutans/S. sanguinis ratio may serve as a meaningful indicator for identifying high risk children for caries. Supported by the New York University College of Dentistry Dean's Award for Student Research and NIH/NIDCR DE 13937.