Extracellular vesicles of Candida albicans show dual effects on Enterococcus faecalis growth and virulence: A laboratory-based investigation

Aim: Previous studies have shown the important relationships between Enterococcus faecalis and Candida albicans in post-treatment endodontic disease (PTED). However, the fungal-bacterial interactions and their possible functional routes are less understood. In this study, we investigated the effect of extracellular vesicles (EVs) derived from C. albicans on E. faecalis growth and pathogenicity.

Methodology: Candida albicans EVs were isolated from a yeast nitrogen base (YNB) medium, and their morphology, size distribution, and protein concentration were observed and identified. The effects of EVs on planktonic E. faecalis were evaluated using growth curves and colony-forming unit counts, whereas the effects on E. faecalis biofilms were determined using scanning electron and confocal laser scanning microscopes. The ability of E. faecalis to resist a detrimental environment, infect dentinal tubules, and biofilm formation on gutta percha was examined. Additionally, the effect of EVs on cell invasion and cytotoxicity of E. faecalis were assessed. Statistical analysis was performed using one-way analysis of variance, and p-values of <.05 were considered significantly different.

Results: Candida albicans EVs were nanoparticles with bilayer membranes and with peak sizes of 111.9 and 230 nm. EVs exhibited a complex effect on E. faecalis and its biofilms; 5 μg/mL of EVs showed inhibitory effects whereas 0.156 μg/mL of EVs facilitated their growth. The EVs showed consistent effects on E. faecalis virulence. Notably, 5 μg/mL of EVs reduced the damage to RAW264.7 cells caused by E. faecalis, as well as the invasion ability of E. faecalis to macrophages and the intracellular survival ability of E. faecalis after macrophage phagocytosis, whereas 0.156 μg/mL of EVs had completely opposite effects.

Conclusion: Candida albicans EVs showed dual effects on E. faecalis growth and virulence in vitro, suggesting C. albicans EVs are involved in fungal-bacterial communication. Moreover, the inhibitory effects exhibited by 5 μg/mL of EVs in vitro may suggest a new agent for the control of E. faecalis.