Role of A. naeslundii in Virulence Factors of Dual-species Biofilms

Objectives: The interaction between different species in dental biofilm influences community behavior and may contribute to dental caries development. To date, the role of Actinomyces naeslundii on virulence factors of dual-species biofilms has not been yet studied. The aim of this study was to evaluate how the interaction between Streptococcus mutans and Actinomyces naeslundii affects virulence factors of dual species biofilms.
Methods: Single- and dual-species biofilms of Streptococcus mutans UA159 or Actinomyces naeslundii ATCC 12104 were formed in hydroxyapatite discs (n=18) using an active attachment model and BHI broth supplemented with 0.2% sucrose. Initial inoculation of biofilms was made with bacterial species containing 10⁴ CFU/mL S. mutans and 10⁸ CFU/mL A. naeslundii. After incubation at 5% CO₂ / 37 °C for 24 h, the following virulence factors were evaluated: cell viability, lactic acid production XTT reduction, total proteins concentration in the extracellular matrix and biomass formation. Data were analyzed by one-way ANOVA and Tukey test at 5% significance level.
Results: A. naeslundii viability was not affected by the presence of S. mutans in dual-species biofilms. However, S. mutans viability in dual-species biofilms was significantly reduced. Lactic acid production in dual-species biofilms was reduced in 50% in comparison to single-species biofilms. For the other virulence factors tested in the present study (total protein, biomass and XTT reduction) there were no statistically significant differences between the growth conditions.
Conclusions: In conclusion, the presence of A. naeslundii at early stages of biofilm development reduced dual-species cariogenicity by decreasing S. mutans viability and lactic acid production in dual-species biofilms.