Novel and conventional assays determining streptococcus mutans abundance in saliva

Abstract

OBJECTIVES: This study aimed to comparatively evaluate the validity of a novel immunoassay and a conventional assay for detecting salivary Streptococcus mutans in a pediatric cohort. METHODS: With an ethical approval from the University of Hong Kong Institutional Review Board (IRB #UW08-400), 190 preschool children aged 3-4 years were recruited from three kindergartens representing low, moderate, and high socio-economic strata in Hong Kong. The abundance of Streptococcus mutans in saliva samples was analyzed with three assay systems viz. a conventional culture-based assay (Dentocult SM), a novel immunoassay (SALIVA-CHECK MUTANS) based on monoclonal antibody technology, and a real-time PCR assay taken as a gold standard. RESULTS: The mean numbers of Streptococcus mutans [log10(CFU/ml saliva)] confirmed by real-time PCR were 4.75+/-1.56, 4.95+/-1.42, and 3.56+/-1.05 for low, moderate, and high socio-economic groups, respectively. Children from families of high socio-economic status harbored significantly lower level of Streptococcus mutans, compared with the rest of participants (p<0.001). The immunoassay accurately categorized salivary samples into two groups with high (≥5X105 CFU/ml) and low (<5X105 CFU/ml) levels of Streptococcus mutans. The sensitivity/specificity was 97.6%/90.6%. The conventional culture-based assay reached a reasonably high sensitivity/specificity (92.8%/81.3%) in identifying children with a moderate (≥104 CFU/ml) level of Streptococcus mutans. However, its sensitivity/specificity in selecting children with high (≥105 CFU/ml) and very high (>106 CFU/ml) levels of Streptococcus mutans were relatively low (78.7%/79.8% and 25.8%/91.8%, respectively). CONCLUSIONS: The monoclonal antibody-based immunoassay, which accurately and rapidly determines Streptococcus mutans abundance in saliva, could be useful for chairside assessment of patients' caries risk.