Investigation of the effect of tyrosol on single and dual biofilms formed by fungal- bacterial (non-albicans Candida spp- Streptococcus mutans) species

The majority of infections are biofilm-related and the produced biofilms are usually polymicrobial. Streptococcus mutans is a bacteria that is common in tooth decay and is resistant to acidic environments. Opportunistic pathogen Candida species colonize the oral cavity. The dual biofilm structure of these two microorganisms, one prokaryotic and the other eukaryotic, is complex. Tyrosol is produced endogenously as a quorum sensing molecule in C. albicans and exhibits antimicrobial and antibiofilm properties when applied exogenously. In this study, inhibitory effects of exogenous tyrosol on the planktonic C. glabrata, C. tropicalis and S. mutans species and on the S. mutans - C. tropicalis dual biofilms were investigated. Our data demonstrate the inhibitory and biofilm-reducing effects of tyrosol on single and dual planktonic and biofilm cells. S. mutans is inhibited at much higher tyrosol concentrations than C. tropicalis. Transmission electron microscope (TEM) data showed that tyrosol damages cells by a multitargeted mechanism. To our knowledge, the physical interaction between bacteria-fungus cells in dual culture was demonstrated for the first time with TEM. In the dual biofilm, tyrosol and amphotericin B reduced the biofilm, hovewer an increased resistance to ampicillin was observed. The application of tyrosol at 2xMIC concentration in the dual biofilm may have induced the biofilm. In cell culture studies, tyrosol suppressed growth at low concentrations and showed a proliferative effect at high concentrations and our data needs to be clarified.