Aims: Mutans streptococci include Streptococcus mutans and Streptococcus sobrinus, which can cause tooth decay. The current study aimed to compare their virulence genes with each other and to correlate them with the clinical data of patients. Materials and methods: Altogether 21 S. mutans and 19 S. sobrinus strains were investigated, originating from 24 children (age 2.7 ± 0.4 years) and 13 mothers (27.3 ± 3.7). The PCR method was applied to detect 11 virulence genes. Caries indices (dmf, decayed/missing/filled; DMFT, decayed/missing/filled teeth) and SM score (Mutans streptococci amount in saliva) were recorded. Results: Most of the S. mutans strains harbored all the virulence genes studied, while S. sobrinus had significantly fewer genes. The genes gbpA, gbpB, wapA and ftf were present in all isolates of S. sobrinus, the spaP, gtfB, vicR, SMU.1037c and SMU.105 genes were present in 41–88% of the isolates, while gtfD and SMU.104 genes were absent in S. sobrinus strains studied. A positive correlation appeared between the biofilm-related vicR and polysaccharide-production-related gtfD genes. In contrast, another polysaccharide-production-related gtfB gene was present in some cases in strains lacking the vicR or gtfD gene. Positive association was found between the presence of adhesion-related spaP gene in pediatric-derived S. sobrinus strains and an increase in SM score. Conclusions: Differences exist between the two common species of mutans streptococci: strains of S. mutans have more virulence genes than that of S. sobrinus, both crucial and virulence enhancing. Deeper research is needed to clarify the mechanisms behind the increased cariogenicity in cohabitation. View Full-Text ►▼ Show Figures This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.