| Summary: | Aims: Mutans streptococci include <i>Streptococcus mutans</i> and <i>Streptococcus sobrinus,</i> 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 <i>S. mutans</i> and 19 <i>S. sobrinus</i> 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 <i>S. mutans</i> strains harbored all the virulence genes studied, while <i>S. sobrinus</i> had significantly fewer genes. The genes <i>gbpA</i>, <i>gbpB</i>, <i>wapA</i> and <i>ftf</i> were present in all isolates of <i>S. sobrinus</i>, the <i>spaP</i>, <i>gtfB</i>, <i>vicR</i>, <i>SMU.1037c</i> and <i>SMU.105</i> genes were present in 41–88% of the isolates, while <i>gtfD</i> and <i>SMU.104</i> genes were absent in <i>S. sobrinus</i> strains studied. A positive correlation appeared between the biofilm-related <i>vicR</i> and polysaccharide-production-related <i>gtfD</i> genes. In contrast, another polysaccharide-production-related <i>gtfB</i> gene was present in some cases in strains lacking the <i>vicR</i> or <i>gtfD</i> gene. Positive association was found between the presence of adhesion-related <i>spaP</i> gene in pediatric-derived <i>S. sobrinus</i> strains and an increase in SM score. Conclusions: Differences exist between the two common species of mutans streptococci: strains of <i>S. mutans</i> have more virulence genes than that of <i>S. sobrinus</i>, both crucial and virulence enhancing. Deeper research is needed to clarify the mechanisms behind the increased cariogenicity in cohabitation.
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