Clinical Analysis of Gene Encoding Collagen-binding Adhesin of Streptococcus mutans

Objectives: Streptococcus mutans is a known to be a pathogen of dental caries and its major cell surface antigens have been widely investigated. Recently, an approximately 120-kDa Cnm protein with binding properties to type I collagen was identified, and its encoding gene (cnm) was cloned and sequenced. The purpose of the present study was to evaluate the association of the presence of cnm-positive S. mutans with the incidence of dental caries in children.

Methods: Expectorated whole saliva specimens were collected from 101 mother-child pairs, from which bacterial DNA was extracted and analyzed by PCR using S. mutans-specific primer sets. Fifty-five S. mutans-positive mother-child specimen pairs were selected and the distribution of the cnm gene in each was analyzed by PCR. In addition, 48 children younger than 8 years old and with precise clinical records were selected from the subjects, and the associations of clinical parameters (defs rate) related to dental caries in primary teeth with the presence of cnm-positive S. mutans were investigated.

Results: Analysis of the 55 mother-child pairs showed that the detection rate of cnm-positive strains in the mothers and children was 32.7% and 40%, respectively. In addition, the rate for cnm-positive children whose mothers also possessed cnm-positive strains was 72%, which was significantly higher than that for those whose mothers did not (9%). In our analysis of the 48 children younger than 8 years, those with cnm-positive saliva showed a significantly higher defs rate than those from whom cnm-negative and S. mutans-negative specimens (P<0.05).

Conclusion: The present results suggest that identification of cnm-positive S. mutans in the saliva may indicate individuals with a high risk for dental caries.