Association of Tyrosol With Chlorhexidine Gluconate Against Streptococcus mutans

Objectives: The aim of this study was to evaluate the effect of tyrosol in combination with chlorhexidine (CHX) gluconate on planktonic cells and biofilms of Streptococcus mutans, alone or associated with Candida albicans and Candida glabrata.
Methods: The effect of drug combination against each strain in planktonic state was assessed through the determination of minimum inhibitory concentration (MIC). Single and mixed-species biofilms were formed on specimens of acrylic resin (AR) and hydroxyapatite (HA) previously coated with human saliva for 1 h. After, the biofilms (24 h) were treated with the drugs alone or in combination twice a day for 1 minute, during 3 consecutive days, totaling 96-h biofilms. The antibiofilm effect was determined by quantification of the metabolic activity (XTT reduction assay) and number of colony-forming units (CFUs). The biofilms’ structure was observed by scanning electron microscopy (SEM). Data were analyzed by two-way ANOVA and Holm-Sidak’s post-hoc test (α= 0.05).
Results: Tyrosol MIC values for all strains reduced drastically when this drug was associated with CHX gluconate. However, the same tendency was not found for CHX gluconate, and the effect of drug combination was classified as indifferent for most of strains. For biofilms of S. mutans alone or associated with Candida species, tyrosol and CHX gluconate (alone or in combination) were not able to cause significant reductions in metabolic activity and number of CFUs. SEM observations confirmed that the biofilms were structurally unaffected by the treatments.
Conclusions: Tyrosol combined with CHX gluconate resulted in an indifferent effect against planktonic cells and biofilms of S. mutans, alone or associated with Candida species. Future studies should explore the combination of tyrosol or CHX gluconate with other antimicrobials against important oral pathogens.