Streptococcus mutans and Streptococcus sobrinus in plaque of Mongolian children

Objective: Substantial epidemiologic evidence links Streptococcus mutans and Streptococcus sobrinus to caries, and numerous laboratory investigations have showed the ability of these strains to synthesize glucans and produce the lactic acid, which causes dental caries. Molecular methods for bacterial identification and enumeration now make it possible to more precisely study the microbiota associated with dental caries and identify closely related species that are difficult to differentiate by traditional, culture-based approaches.

The objective ot the study was to detect S. mutans and S. sobrinus by PCR, and to compare their presence with the incidence and risk of dental caries in Mongolian children.

Materials and methods: Forty-one preschool children aged 3-5 years and 40 school children aged 12-15 years were enrolled in this study. The subjects received a dental examination according the WHO caries diagnostic criteria. Caries risk assessment was carried out using the Cariostat test developed based on the evaluation of acidogenicity of plaque microorganisms. Dental plaque was collected by swabbing buccal surfaces of maxillary molars by a sterile cotton swab. Oligonucleotide primers SD10 and SD20 for S. mutans and SOF14 and SO1623 for S. sobrinus designed on the basis of nucleotide sequences of dextranase genes were used for amplification of species-specific amplicons.

Results: In preschool children, the prevalence of S. mutans and S. sobrinus were 100% and 36.6%, respectively; 26 (63.4%) were positive for S. mutans alone, 15 (36.6%) were positive for both S. mutans and S. sobrinus. In school children, the prevalence of S. mutans and S. sobrinus were 100% and 25%, respectively; 30 (75%) carried S. mutans only, 10 (25%) both S. mutans and S. sobrinus.

Conclusion: The caries incidence and caries risk of children positive for both S. mutans and S. sobrinus were higher than those positive for S. mutans alone.