Chlorhexidine combined with curcumin-mediated photodynamic treatment effectively inhibits biofilm formation by clinical Candida isolates from the oral cavity

Abstract

This study evaluated the efficacy of chlorhexidine (CHX) in combination with curcumin-mediated photodynamic therapy (CUR-PDT) against clinical Candida spp. isolates. Seven strains were analyzed, including Candida albicans (Ca2, Ca4, CaATCC 10,231) and Candida krusei (Ck7, Ck8, Ck11, Ck12), previously characterized for their biofilm-forming ability using the crystal violet assay after 48 h of incubation in BHIS medium at 35.5 °C, with an initial inoculum of approximately 1–5 × 10⁵ CFU/mL. Antifungal activity was assessed through the minimum biofilm inhibitory concentration (MBIC₅₀) under both irradiated and non-irradiated conditions using blue LED light at 450 nm (20 and 100 J/cm²). CHX alone exhibited MBIC₅₀ values ranging from 3.71 to 14.84 µM. CUR showed no inhibitory activity in the absence of light, with no measurable MIC or MBIC₅₀ values. Upon irradiation, CUR exhibited MBIC₅₀ values ranging from 4 to 64 µM, depending on the strain and light dose. The combined CHX + CUR treatment under 100 J/cm² irradiation demonstrated a pronounced additive effect, reducing MBIC₅₀ values to 0.625 µM for all strains except Candida albicans Ca2, which required 1.25 µM. This combination achieved biofilm inhibition rates exceeding 90 % (p < 0.05). These findings indicate that CHX combined with CUR-PDT under high-dose irradiation significantly enhances biofilm inhibition in Candida spp., supporting its potential as a promising antifungal strategy for the management of biofilm-associated infections.