In vitro Evaluation of Synergistic Inhibitory Effect of Propolis and Chlorhexidine on Biofilm Cells of Oral Pathogens

Background: Dental plaque is a microbial biofilm that can source various oral diseases. Objectives: This study aimed to investigate the synergistic anti-biofilm effect of chlorhexidine (CHX) and propolis aqueous extract on Streptococcus mutans and Staphylococcus aureus. Methods: This study, performed in October 2021, determined theminimumbiofilm inhibitory concentration (MBIC) andminimum biofilm eradication concentration (MBEC) of CHX 0.2% and propolis aqueous extract against S. mutans and S. aureus prepared from the cell bank of the Pasteur Institute of Iran. Also, the in vitro synergistic effect of these two compounds was evaluated on the biofilm inhibition and eradication of the studied bacteria using the checkerboard method. Results: The MBIC of chlorhexidine was 125 g/mL for both S. aureus and S. mutans, while the MBIC of propolis aqueous extract was 937.5 and 3750 g/mL, respectively. Also, the MBEC of chlorhexidine was 250 and 500 g/mL for S. aureus and S. mutans, while the MBEC of propolis was 1875 and 7500 g/mL, respectively. Combining the two substances showed a synergistic effect in inhibiting biofilm formation (P 0.05) while they had an indifferent effect on biofilm eradication. Conclusions: This study concluded that although CHX is one of the most common and vital oral disinfectants in oral diseases, propolis may also be used, as an alternative mouthwash with reliable natural antimicrobial properties, alone or combined with CHX as a moderator of its side effects.