Distribution of oral Streptococcus mutans and its correlation with dental caries in children of Bortala Mongolian Autonomous Prefecture

To study the detection rate of Streptococcus mutans in oral cavities of 3-5- year- old Han, Uygur and Mongolian children in Bortala Mongolian Autonomous Prefecture, and the correlation between genotype and dental caries of preschool children.

Ninety children were randomly selected from the sample bank of children′s oral epidemiological survey data in the Bozhou area of Xinjiang. Forty-five children were included in the high caries group (more than 5 missing teeth), and 45 children were included in the noncaries group (0 missing teeth); each group comprised 15 children of each of the Han, Uygur and Mongolian nationalities. Plaque samples were collected and cultured with light saliva-bacillin agar medium and brain-heart infusion medium. Streptococcus mutans were cultured, and clinical isolates were further isolated and identified by Gram staining, biochemical identification and polymerase chain reaction. Genotype distribution was detected by random primer polymerase chain reaction.

The detection rate of Streptococcus mutans in the 90 included children was 75.5%. The detection rate of Streptococcus mutans in the high caries group was 86.7%, which was significantly higher than that in the caries-free group (64.4%) (P＝0.014). There was no significant difference in the distribution of Streptococcus mutans among Han, Uygur and Mongolian nationalities (P＝0.457). A total of 549 clinical strains of Streptococcus mutans were obtained, and 113 different genotypes were found. In the high caries group, 61.5% carried more than one genotype of Streptococcus mutans, and 37.9% of the caries-free group had more than one genotype. The genetic polymorphism of Streptococcus mutans in the high caries group was significantly higher than that in the caries-free group (P＝0.035). Spearman correlation analysis showed that there was a positive correlation between oral Streptococcus mutans gene polymorphism and caries sensitivity (r＝0.258, P＝0.034).

The distribution of Streptococcus mutans in children′s oral cavity in the Bozhou area was different between the high caries group and the caries-free group, but there was no difference among nationalities. Streptococcus mutans in the high caries group had more genotypes than those in the caries-free group. The genetic polymorphism of Streptococcus mutans might be related to the caries-causing ability of Streptococcus mutans.