Tyrosol activity against biofilms formed on hydroxyapatite discs

Objectives: The purpose of this study was to analize the activity of tyrosol at different concentrations on pre-formed biofilms of Streptococcus mutans ATCC 25175 alone or associated with Candida albicans ATCC 10231 and Candida glabrata ATCC 90030, formed on hydroxyapatite discs (HA).
Methods: HA discs were placed into 24-well plates and inoculated with S. mutans (10⁸ cells/mL in artificial saliva (AS)) alone or in association with C. albicans and C. glabrata (10⁷ cells/mL in AS). After 24h of incubation, the treatments with tyrosol (diluted in AS) at 100 and 200 mM were performed twice a day for one minute, in the following 3 days, totaling 96-h biofilms. AS without tyrosol and chlorhexidine gluconate (CHG; 0.37mM) were used as negative and positive controls, respectively. Tyrosol activity was evaluated through total biofilm biomass quantification and evaluation of metabolic activity. Scanning electron microscopy (SEM) images were used to investigate the biofilm structure. Data were analyzed by one-way ANOVA and Holm-Sidak post-hoc test (α = 0.05).
Results: At the concentrations tested, tyrosol was unable to reduce significantly the total biomass and metabolic activity of all biofilms investigated. With regard to biofilm activity, CHG promoted significant decreases of 71.4 % and 81.5 %, respectively for S. mutans alone and in association with Candida species. SEM observations confirmed that pre-formed biofilms were structurally unaffected by the treatments with tyrosol.
Conclusions: In summary, tyrosol at 100 and 200 mM has no activity against pre-formed biofilms of S. mutans alone or associated with Candida species. However, additional studies with a large number of strains and with biofilms at different stages of development are needed in order to elucidate the real role of tyrosol as an antibiofilm agent.