Mutans and other oral streptococcal colonization with age in children

Objective: In this study, we developed the species-specific PCR assays for mutans and other five oral streptococcal species, and assessed cross-sectionally the colonization of the streptococci with age in plaque samples from children in relation to the caries prevalence. Methods: The species-specific PCR assays targeting gtf and 16S rRNA genes have been developed for Streptococcus mutans, S. sobrinus, S. gordonii, S. sanguinis, S. oralis, S. anginosus and S. salivarius. The PCR assays enabled to specifically detect 0.5 to 5 pg of genomic DNA, corresponding to 100 CFU of bacteria, of each species. After a clinical examination including caries score, the plaque samples were obtained from 320 children (0 to 15 year olds, 20 subjects in each age) with informed consent of their parents. The bacterial DNA was isolated with a DNA purification kit. The colonization of each streptococcal species in the plaque sample was assessed by the species-specific PCR methods. Results: Among seven streptococci, S. mutans (68.8%) was most frequently detected, and S. sobrinus (15.0%) and S. gordonii (17.2%) were scarcely colonized. S. sobrinus was found in the plaque samples from S. mutans-positive subjects. The percentages of S. mutans- and S. anginosus-positive subjects increased with age, while the percentage of S. sanguinis-positive subjects decreased. Further, the subject-based analysis noted a positive correlation between S. mutans colonization and the caries score (p < 0.05). Conclusions: The present cross-sectional study using the developed highly sensitive species-specific PCR assays indicated that many oral streptococcal species including mutans streptococci could colonize quite early in childhood with plaque development, and thereafter the proportional changes of increase of S. mutans and S. anginosus and decrease of S. sanguinis could occur with age. However, S. mutans was the predominant species that correlated with caries prevalence in children.