Abstract
This study aimed to investigate the effect of an ethanolic extract of propolis (EEP) on the expression of genes associated with the adherence of Streptococcus mutans (S. mutans) to the tooth surface. A total of 10 S. mutans isolates, obtained from individuals with and without dental caries, were included in the study and identified using biochemical methods. The biofilm-forming ability was assessed using the microtiter plate method. Then, the antibacterial effect of the EEP was evaluated through the agar well diffusion and broth microdilution assay. Real-time polymerase chain reaction as employed to investigate the impact of sub-MIC (minimum inhibitory concentration) of EEP on the expression of gtfB, gtfC, gbpB, and ftf genes. In the standard microtiter plate method, 30% of the isolates produced strong biofilms (n = 3), 50% produced moderate biofilms (n = 5), and 20% produced weak biofilms (n = 2). The EEP demonstrated significant antimicrobial activity against S. mutans, with concentrations ranging from 30% to 100% (1.2–4 mg/mL) producing a notable increase in inhibition zone size compared with the control (p < 0.05), as measured by the well diffusion method. The MIC for all strong biofilm-producing isolates was found to be 1.2 mg/mL (30% EEP concentration). Gene expression analysis revealed a reduction in the expression of all target genes in the presence of EEP. Among the genes studied, gtfB exhibited the most substantial reduction with a 4.63-fold decrease (p < 0.001), while ftf showed the smallest decrease at 2-fold (p < 0.05). These findings suggest that the EEP has a notable antimicrobial effect, particularly against biofilm-producing strains. Moreover, the observed downregulation of key genes involved in biofilm formation and adhesion (gtfB, gtfC, ftf, and gbpB) highlights the potential of propolis as a natural agent for combating S. mutans infections and inhibiting biofilm formation.
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