Effect of mouthwashes on the composition and metabolic activity of oral biofilms grown in vitro

OBJECTIVE: The aim of this study was to determine the effect of an oxygenating mouthwash compared to two other established mouthwash products on bacterial composition and metabolic activity of oral biofilms in vitro. MATERIAL AND METHODS: Twelve healthy subjects participated as donors. Plaque-saliva mixture inoculated biofilms were grown and treated with 3 different chemotherapeutic mouthwashes [amine fluoride/stannous fluoride (MD), oxygenating agent (AX), chlorhexidine 0.12 % (PA), and water (W)]. Effects of treatments were assessed on biofilm composition (16S rRNA gene amplicon sequencing), production of organic acids (formate, acetate, lactate, propionate, butyrate using capillary electrophoresis), and viability of the remaining biofilm (CFUs). RESULTS: Microbial profiles of biofilms clustered per inoculum donor and were dominated by the genera Veillonella, Streptococcus, and Prevotella. Microbial diversity was only reduced after PA treatment. Significant changes in composition occurred after treatment with AX, resulting in lower proportions of Veillonella and higher proportions of non-mutans streptococci. Production of all organic acids after PA and lactate after MD was significantly lower as compared to W. AX resulted in reduction of acetate, butyrate, and propionate and increase in lactate production (p < 0.05). Viable counts were significantly lower after PA and AX treatments compared to W, while no significant reduction was observed after MD. CONCLUSIONS: All studied mouthwashes affected the in vitro biofilms differently. The effects of the AX treatment were the most prominent which resulted in changes of the bacterial composition and metabolism. CLINICAL IMPLICATIONS: Awareness by the dental team that mouthwashes can change the bacterial composition and metabolism is important when advising its use.