Antibiofilm effect of Curcuma longa L. extract in antimicrobial photodynamic therapy against Enterococcus faecalis

Enterococcus faecalis is associated with persistent endodontic infections due to its ability to form resistant biofilms. Antimicrobial photodynamic therapy (aPDT) has emerged as a promising alternative approach. This study evaluated the antibiofilm activity of an ethanolic extract of Curcuma longa L. against E. faecalis ATCC 29,212, with and without aPDT.

An in vitro biofilm model was used. The minimum biofilm inhibitory concentration (MBIC) was determined. Biofilms were treated with the C. longa extract (7.81-2000 µg/mL) under LED irradiation (aPDT) and without light activation. Chlorhexidine (2%) served as a positive control while untreated biofilms served as negative control. Biofilm biomass was quantified by optical density, and statistical analysis was performed using ANOVA and Tukey's test (p < 0.05).

The MBIC was 62.5 µg/mL. aPDT significantly reduced biofilm formation compared to the negative control (p < 0.001). The highest inhibitory effects were observed at 31.25 and 62.5 µg/mL, with effects comparable to those of 2% chlorhexidine under in vitro conditions. The highest concentration (2000 µg/mL) showed reduced activity and a potential paradoxical, concentration-dependent effect. Without light activation, the extract also showed antibiofilm activity, but to a lesser extent.

Curcuma longa L. exhibits concentration-dependent antibiofilm activity against E. faecalis, enhanced by aPDT. Reduced efficacy at higher concentrations may be related to aggregation and self-quenching of curcumin. Despite chlorhexidine remaining the clinical reference, C. longa showed comparable effects at optimal concentrations. Limitations include the absence of a light-only control, lack of CFU confirmation, and potential staining risk.