Development of a herbal mouthwash containing a mixture of essential oils and plant extracts and<i>in vitro</i>testing of its antimicrobial efficiency against the planktonic and biofilm-enclosed cariogenic bacterium<i>Streptococcus mutans</i>

A herbal mouthwash containing essential oils of holy basil and mountain tea, extracts of St John's wort and European goldenrod (Bucovia™) and cetylpyridinium chloride, was developed and <i>in vitro</i> tested for its efficiency against biofilm formation by <i>Streptococcus mutans</i>, together with its eradicating activity against already preformed (48 h with saccharose) streptococcal biofilm. The minimum inhibitory (MIC) and bactericidal concentrations (MBC) of the final formulation, as well as of its individual components, were initially determined. The results revealed that the mouthwash needed to be applied at two-times its MIC (0.63% v.v^-1) to completely inhibit biofilm formation by <i>S. mutans</i>, which was otherwise capable of developing a robust biofilm on the tested surface. Once fully developed, the matrix of the biofilm was found to contain a significant amount of exopolysaccharides protecting the cells, being impossible to eradicate even when exposed to pure mouthwash for 15 min, highlighting the great recalcitrance of biofilm-embedded <i>S. mutans</i>.