Antibacterial and Antibiofilm Activity of Commercial Mouthwashes against Streptococcus mutans: An In Vitro Study

Aim: The present study investigated the effects of four commercial mouthwashes (MWs) on the growth and biofilm formation of Streptococcus mutans. Materials and methods: Four types of MWs, namely Listerine®, TheraBreath®, Garglin Original®, and Himalayan Pink Salt®, were selected, and chlorhexidine (CHX) solution was used as a positive control. As an antibacterial test, the disk diffusion method was tested with four types of MW diluted to 100, 50, 20, 10, or 5%, respectively, and then colony-forming units (CFU) assay was performed with the 50% diluted MWs. In addition, the effect of MWs on the caries activity of S. mutans was confirmed by human saliva-coated biofilm formation assay and pH measurement. Data were expressed as means ± standard deviations, and the significance between variables was analyzed by the one-way analysis of variance (ANOVA). Statistical significance was defined as p-value <0.05. Results: The antibacterial activity against S. mutans by the disk diffusion method increased with the concentration of the MWs, and in particular, most of the 50% diluted MWs showed similar effects to the undiluted original solutions. All four 50% diluted MWs significantly inhibited S. mutans colonization in the CFU assay. In addition, the pH of the culture medium of S. mutans treated with each 50% diluted MW did not fall below the critical pH of 5.5 and was maintained above 7.0. Finally, oral biofilm formation by S. mutans was statistically significantly inhibited by >50% by all 50% diluted MWs. However, there were no significant differences between the MWs. Conclusion: The results of the current study confirmed that all commercial MWs used in the experiment showed high antibacterial and antibiofilm activity against S. mutans even at 50% dilution. Clinical significance: The present study provides findings that commercial MWs, even when diluted to 50%, exhibit similar antibacterial and antibiofilm effects as the original solution. Oral health professionals can use this information to suggest diluted MWs for use in patients who are reluctant to use MWs due to irritation.