# In vitro antibiofilm activity of tyrosol against single and dual-species biofilms of Candida tropicalis and Streptococcus mutans

## TL;DR

Tyrosol, a natural compound, reduces biofilm formation by Candida tropicalis and Streptococcus mutans, showing potential as a treatment for oral infections.

## Contribution

The study demonstrates tyrosol's antibiofilm activity against dual-species biofilms and its selective cytotoxicity.

## Key findings

- Tyrosol inhibited biofilm formation and microbial viability in dual-species biofilms.
- Tyrosol caused structural changes in biofilms as observed via microscopy.
- Tyrosol showed selective cytotoxicity to fibroblast cells at higher concentrations.

## Abstract

The cross-kingdom biofilm structure formed by Candida tropicalis and Streptococcus mutans may increase caries formation. The aim of this study was to evaluate the in vitro effect of the exogenous tyrosol on single- and dual-species biofilms as well as planktonic cultures formed by C. tropicalis and S. mutans.

The antimicrobial efficacy of tyrosol was evaluated through broth microdilution, colony-forming unit (CFU) enumeration, and XTT reduction tests to assess cell viability and metabolic activity. Transmission electron microscopy (TEM) was used to examine ultrastructural changes in planktonic cells. Biofilm dynamics were visualized via scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The in vitro cytotoxicity of tyrosol was evaluated using NIH/3T3 fibroblast cells.

XTT results showed that the biofilm-reducing effect of amphotericin B (AMB) on single C. tropicalis biofilm at the minimum inhibitory concentration (MIC) and 2× MIC was significantly higher than that of control (47% and 48%, respectively) (p < 0.05). Tyrosol also had a metabolic activity-reducing effect on single C. tropicalis biofilm, but this effect was not statistically significant (39% at 2× MIC and 42% at MIC). Tyrosol and ampicillin (AMP) had no significant reducing effect on single S. mutans biofilm cells (p > 0.05). However, AMP resistance increased in dual culture. CFU enumeration, TEM, SEM, and CLSM data supported these findings. The effect of tyrosol on NIH/3T3 fibroblast cells was suppressive at low concentrations (1–4 mg/mL) and enhancing at high concentrations (4.5–20 mg/mL).

This study investigated the antimicrobial and antibiofilm properties of tyrosol against C. tropicalis and S. mutans, individually and in combination. The results showed that tyrosol inhibited growth and biofilm formation, particularly in dual-species biofilms. Although S. mutans had greater resistance, overall microbial viability was reduced. Despite some observed increase in AMP resistance, tyrosol was selectively cytotoxic, indicating its promise as a natural therapeutic agent pending further research.

This study examined the effects of exogenous tyrosol on Candida tropicalis and Streptococcus mutans dual-species biofilms. Tyrosol reduced biofilm formation but increased ampicillin resistance. Microscopy analyses showed structural changes, highlighting the antimicrobial activity of tyrosol. These findings suggest its potential role in biofilm-associated oral infections, warranting further investigation.