Effect of propolis on Streptococcus mutans biofilm formation

Objective: To evaluate the susceptibility of S. mutans during growth as a biofilm in the presence of different concentrations of propolis. Material and Methods: Three different concentrations of ethanolic extract of propolis (10%, 5%, and 2.5%) were used to evaluate its potential to attenuate the biofilm formation of S. mutans (ATCC 25175) on microplates. A crystal violet staining method was performed to measure the optical density (OD) of the biofilm biomass after 3 h and 18 h time periods. All the experiments were performed in triplicate, and the obtained data were expressed as mean ± standard deviation. A two-tailed Student’s t-test was used to determine the different abilities of biofilm formation between the treated and control groups of the bacteria film in the presence of propolis. A p-value of <0.05 was taken as a significant value. Results: The OD levels (determined using an ELISA reader) obtained after growing S. mutans as a biofilm in the presence of propolis were similar (p>0.05) to those of the control (S. mutans grown in tryptic soy broth + 1% sucrose). Conclusion: All the tested concentrations of propolis added to the growth medium did not inhibit the biofilm formation of S. mutans. Since biofilms consist of bacterial cells and extracellular matrices, we hypothesize that the extracellular matrix may have interfered with the antimicrobial properties of the tested propolis.