Effect of tyrosol on Streptococcus mutans biofilms

Author(s)

Laís Salomão Arias

• Document type: Master's Dissertation
• Press: Araçatuba. 2016-03-03.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Odontologia. Araçatuba
• Defense date: 2016-02-29
• Advisor: Douglas Roberto Monteiro; Alberto Carlos Botazzo Delbem

Abstract

Tyrosol is a quorum-sensing molecule (QS) that participates in the control of Candida albicans morphogenesis. However, its effect as an antimicrobial agent on Streptococcus mutans biofilms remains unknown. Thus, the aim of this study was to evaluate the effect of tyrosol at different concentrations on the acid production and biofilm formation by S. mutans ATCC 25175, as well as to quantify pre-formed biofilms of this species developed on hydroxyapatite (HA) specimens and treated with tyrosol. Minimum inhibitory concentration (MIC) of tyrosol against planktonic cells was determined in accordance with the microdilution method. Subsequently, S. mutans biofilms were formed during 48 hours on HA specimens in the presence of different concentrations of tyrosol (11.25, 22.5, 50, 100 and 200 mmol l-1), using artificial saliva as culture medium. Next, the acid production was assessed by pH determination of the medium, while the biofilm formation was determined through quantification of total biomass (TB), metabolic activity (MA) and number of colony-forming units (CFUs). Further, S. mutans pre-formed biofilms (24 h) were treated with tyrosol at 100 and 200 mmol l-1 twice a day for 1 min, during 3 days, totaling 96-h biofilms. Then, the antimicrobial activity was evaluated through quantification of TB, MA, number of CFUs and composition of biofilms’ extracellular matrix (proteins and carbohydrates). Chlorhexidine gluconate (490 μmol l-1) was used as positive control. Data were analyzed by one-way ANOVA, followed by Tukey’s and Holm-Sidak's tests (α = 0.05). Scanning electron microscopy (SEM) observations were performed in order to analyze biofilms’ structure. MIC of tyrosol was 90 mmol l-1. Tyrosol at sub-inhibitory concentrations (11.25 and 22.5 mmol l-1) was not able to significantly reduce acid production by S. mutans biofilms. However, biofilms formed in the presence of tyrosol at 50, 100 and 200 mmol l-1 showed significant decreases in MA and number of CFUs, ranging from 23.4 to 85.5 % and 1.19 to 4.54-log10, respectively. For pre-formed biofilms, the treatments with tyrosol did not promote significant reductions, except for MA of biofilm treated with 200 mmol l-1 tyrosol, which showed a 40 % reduction (p = 0.015) compared to the negative control. Moreover, treatment with 200 mmol l-1 tyrosol resulted in a significant increase in the protein content of the extracellular matrix of S. mutans pre-formed biofilm. SEM observations confirmed the results of CFU enumeration. In conclusion, tyrosol showed better effects on biofilm formation than on pre-formed biofilm, and this QS molecule was not able to reduce acid production by S. mutans biofilms. These results may be useful in the development of topical therapies focused on preventing biofilm-associated oral diseases, such as dental caries. (AU)

• FAPESP's process: 14/05507-9 - Effect of Tyrosol on the lactic acid production and on the ability to form biofilms by Streptococcus mutans
• Grantee: Laís Salomão Arias
• Support Opportunities: Scholarships in Brazil - Master