Intraspecies transformation of Streptococcus mutans virulence in vitro

Objective: The present study evaluated the virulence transformation within intraspecies of Streptococcus mutans isolated from caries-free and caries-active subjects.

Methods: A total of 165 S. mutans isolates from caries-free subjects and 115 isolates from caries-active subjects were obtained from samples of dental plaque and identified by PCR. Virulence of isolated strains was measured by glucosyltransferases (GTFs) activity, acid production and acid tolerance test. Virulence transformation within intraspecies of different strains were performed by mixed culture of two or three strains with different virulence properties. Isolate colonies of filial generation bacteria on an agar plate were enrichment incubated and estimated virulence again.

Results: The results showed a significant difference between each one in virulence (GTFs activity, aciduricity, and acidogenesis) for 280 strains of S. mutans. The high virulent strains of Streptococcus mutans could isolated from caries-free subjects and low virulent ones could isolated from caries-active subjects. The highest virulence characteristics do not fasten on a same strain. Virulence of strains of a filial generation did not show differences between each other within the same microbial community, but very differ from their parent strains.

Conclusions: Hence, our results reflect that the virulence may be transferred among strains within intraspecies of Streptococcus mutans. Horizontal gene exchange among individuals of the same species may occur in a microbial niche.