Materials and methods:87 S-ECC (dt≥5) and 91 caries-free children aged 42-54 month-old were recruited. The caries scores were recorded. Stimulated saliva was collected and submitted to selective cultivation. MS colonies were enumerated. MS strains DNA was identified as S. mutans or S. sobrinus by PCR. The genomic fingerprint analysis of S. mutans and S. sobrinus was carried out using AP-PCR.
Results:S. mutans was isolated from 95.40% S-ECC and 62.64% caries-free children. While S. sobrinus was from 18.39% S-ECC and 3.30% caries-free children. The count of MS colonies in S-ECC children was significantly higher than in caries-free children. 15 S-ECC and 2 caries-free children harbored both S. mutans and S. sobrinus. One child in each group harbored S. sobrinus only. The average score of dmft (11.93±2.49) in children harboring both microbes was significantly higher than those harboring S. mutans only (9.88±3.05). 730 S. mutans isolates were classified into 337 distinct genotypes by fingerprint analysis, while 53 S. sobrinus isolates into 22 distinct genotypes. One to five genotypes of S. mutans were colonized in one sample. Genotypes of S. sobrinus from S-ECC children ranged from 1 to 3, and only one genotype in each caries-free child. The fingerprints of S. mutans and S. sobrinus from S-ECC individuals exhibited greater diversity than those from caries-free individuals. S. mutans from unrelated individuals displayed distinctive fingerprints. The same genotype of S. sobrinus was present in three unrelated S-ECC subjects. The number of S. sobrinus genotypes was related to their dmft scores in S-ECC children.
Conclusions: DNA fingerprints of S. mutans and S. sobrinus isolates from 3-4 year-old children displayed genetic polymorphism, which increased the risk of caries. The same genotype of S. sobrinus was present in unrelated subjects.