The determination of the composition of the microbial community in the oral cavity is usually based on cultivation methods; however, nearly half of the bacteria in the saliva and the dental plaque are not cultivable. In this study, we evaluated the difference in oral microbial diversity between children with severe early-childhood caries (S-ECC) and caries-free (CF) controls by means of a cultivation-independent approach called denaturing gradient gel electrophoresis (DGGE). Pooled dental plaque samples were collected from 20 children aged 2 to 8 years. Total microbial genomic DNA was isolated from those subjects, and a portion of the 16S rRNA gene locus was PCR amplified by using universal primers. We observed that the mean species richness of the bacterial population was greater in the CF children (n ‫؍‬ 12) (42 ؎ 3.7) than in the S-ECC children (n ‫؍‬ 8) (35 ؎ 4.3); the difference was statistically significant (P ‫؍‬ 0.005). The overall diversity of plaque samples as measured by the Shannon index was 3.5 for the S-ECC group and 3.7 for the CF group (P ‫؍‬ 0.004). Differences in DGGE profiles were distinguished on the basis of a cluster analysis. Sequence analysis of excised DGGE bands consisted of 2.7 phylotypes, on average. After adjusting for the number of observed bands, we estimated that the S-ECC group exhibited 94.5 total phylotypes and that the CF group exhibited 113.4. These results suggest that the microbial diversity and complexity of the microbial biota in dental plaque are significantly less in S-ECC children than in CF children.

The aim of this study was to examine the colonization of Streptococcus mutans and Streptococcus sanguinis in the oral cavity and the association with severe early childhood caries (S-ECC). Saliva and plaque samples were collected from 14 S-ECC children and 8 caries-free (CF) children. All S-ECC children were S. mutans positive; 100% of CF children and 93% of S-ECC children were S. sanguinis positive. The children’s caries severity was positively correlated with levels of S. mutans (p < 0.001), total oral streptococci (p < 0.01), total cultivable oral bacteria (p < 0.05), and children’s age (p < 0.05). Logistic regression analysis showed that the interaction of S. sanguinis with S. mutans was a significant factor associated with the caries status in children, suggesting that the relative levels of these two microorganisms in the oral cavity play an important role in caries development.

Streptococcus mutans is the major microbial pathogen associated with dental caries in children. The objectives of this study were to design and evaluate species-specific primers for the identification of S. mutans. Validation of the best primer set, Sm479F/R, was performed using seven S. mutans reference strains, 48 ATCC non-S. mutans strains, 92 S. mutans clinical isolates, DNA samples of S. mutans-Streptococcus sobrinus or S. mutans-Streptococcus sanguinis, and mixed bacterial DNA of saliva samples from 33 18-month-old children. All of the S. mutans samples tested positive, and no PCR products were amplified from members of the other streptococci or nonstreptococci strains examined. The lowest detection level for PCR was 10(-2) ng of S. mutans DNA (c. 4.6 x 10(3) copies) in the test samples. The results of this study suggest that the Sm479F/R primer pair is highly specific and sensitive for identification of S. mutans in either purified or mixed DNA samples.