AP-PCR detection of Streptococcus mutans and Streptococcus sobrinus in caries-free and caries-active subjects

The aim of the study was to identify the number and distribution of genotypes of Streptococcus mutans ( S . mutans ) and Streptococcus sobrinus ( S . sobrinus ) isolated from caries-free and caries-active subjects. Non-stimulated saliva, buccal smooth surface of the right upper teeth, fissures of sound occlusal surface, and carious surface were sampled from 7 caries-free and 7 caries-active (DMFT ≥ 6) students aged 22–24 years. S . mutans and S . sobrinus were isolated using Chelex-100 and primarily identified by colony morphology and biochemical characteristics. The isolates of S . mutans were genotyped using arbitrarily primed polymerase chain reaction. A total of 516 isolates of S . mutans were genotyped from 47 sites in 14 students, and 44 different genotypes were determined. All of the caries-free individuals harbored S . mutans but not S . sobrinus , although individuals 3 and 7 had no S . mutans in their saliva. The CFU value of S . mutans on carious surfaces was the highest, and values in saliva, fissures, and occlusal surfaces were higher in caries-active individuals than in caries-free individuals. We detected 28 genotypes of S . mutans in caries-free individuals, each of who carried more than 3 genotypes. However, we found only 16 genotypes of S . mutans in caries-active individuals, each of who carried no more than 3 genotypes. More genotypes are harbored in the saliva, fissures, and smooth surfaces of caries-free individuals than of caries-active individuals. The proportion of samples positive for S . mutans and S . sobrinus was significantly higher in caries-active individuals than in caries-free individuals, and the presence of these species is a risk factor for high DMFT in dental caries. Isolates of S . mutans exist that have apparent genetic diversity. The genotypes of isolates might relate to differences in caries susceptibility.