Mutans Streptococci Aciduricity & Acidogenicity: Relationships to Childhood Caries Risk

Objectives: To evaluate aciduricity and acidogenicity properties of mutans streptococci (MS) strains isolated from early childhood caries (ECC) and caries free (CF) children age and gender matched (2-6 years old). Methods: Fifty-six MS strains from twenty ECC children and 8 MS strains from twenty CF children were recovered on MSB plates and then inoculated in BHI broth at pH 3.5-6.0, in 0.5 increments. After 48 hours, aciduricity and acidogenicity were measured. Acidogenicity was evaluated by the fall in pH. Aciduricity was assessed by measuring growth as optical density (OD) at each pH and bacterial survival by BHI plates. Results: Out of the twenty subjects in the CF group only 6 had MS bacteria; conversely all of the twenty children had MS in the ECC group. Neither mean minimum survival pH nor mean growth (OD) at lower pH, aciduricity, were significantly different (t test, P>0.05) between ECC and CF groups. However, ECC strains grew more at pH 5.5 and 6.0 (P<0.05, Mann-Whitney test) than CF strains. The mean number of strains that were more aciduric was higher in ECC than CF (P<0.05, Mann-Whitney test). At pH 5.0-6.0 more strains produced acid (acidogenicity) than average in ECC compared to CF strains (P<0.05, Mann-Whitney test). Conclusion: Aciduricity and acidogenicity virulence factors of mutans streptococci contribute to the complex network of caries risk status. Support: NIH/NIDCR T32 DEO7306