The Effect of Sub-Lethal Successive Applications of Photodynamic Therapy on Candida albicans Biofilm Depends on the Photosensitizer.

This study aimed to evaluate the potential of successive applications of sub-lethal doses of the antimicrobial photodynamic therapy (aPDT) mediated by Photodithazine® (PDZ) and curcumin (CUR) associated with LED in the viability, reactive oxygen species (ROS) production, and gene expression of Candida albicans. The microbial assays were performed using planktonic cultures and biofilms. Ten successive applications (Apl#) were performed: aPDT (P+L+; C+L+), photosensitizer (P+L-; C+L-), and LED (P-L+; C-L+). Control groups were used (P-L-; C-L-). The viability of C. albicans was determined by cultivating treated cultures on agar plates with or without fluconazole (FLU). In addition, the ROS detection and expression of SOD1, CAP1, and ERG11 genes were determined. For planktonic cultures, no viable colonies were observed after Apl#3 (without FLU) and Apl#2 (with FLU) for either photosensitizer. Biofilm treated with P+L+ resulted in the absence of cell viability after Apl#7, while C+L+ showed ~1.40 log10 increase in cell viability after Apl#2, regardless of FLU. For both photosensitizers, after the last application with viable colonies, the production of ROS was higher in the biofilms than in the planktonic cultures, and SOD1 expression was the highest in P+L+. A reduction of CAP1 and ERG11 expression occurred after P+L+, regardless of FLU. C+L+ had a higher level of ROS, and the treatments were non-significant for gene expression. Sub-lethal doses of aPDT mediated by CUR could induce C. albicans resistance in biofilms, while C. albicans cells in biofilms were susceptible to aPDT mediated by PDZ.

Lactobacillus casei reduces the extracellular matrix components of fluconazole-susceptible Candida albicans biofilms.

Fluconazole-sensitive (CaS) and -resistant (CaR) C. albicans were grown as single-species and dual-species biofilms with Lactobacillus casei (Lc) and Lactobacillus rhamnosus (Lr). Single-species Lc and Lr were also evaluated. Biofilm analysis included viable plate counts, the extracellular matrix components, biomass, and structural organization. Lc reduced the viability of CaS, water-soluble polysaccharides, and eDNA in CaS + Lc biofilm. Lc biofilm presented more eDNA than CaS. The total biomass of CaS + Lc biofilm was higher than the single-species biofilms. The viability of Lc and Lr was reduced by CaR dual-species biofilms. The total and insoluble biomass in CaS + Lr was higher than in single-species CaS biofilms. Lc hindered the growth of CaS, and their association hampered matrix components linked to the structural integrity of the biofilm. These findings allow understanding of how the implementation of probiotics influences the growth of C. albicans biofilms and thereby helps with the development of novel approaches to control these biofilms.

Successive applications of Antimicrobial Photodynamic Therapy effects the susceptibility of Candida albicans grown in medium with or without fluconazole.

Antimicrobial Photodynamic Therapy (aPDT) was introduced as a therapy due to resistance that microorganisms have developed to conventional drugs. The study aimed to evaluate the potential of successive applications of aPDT in effecting Candida albicans susceptibility and also whether the presence of fluconazole effected the recovery of the fungi in the culture medium. Planktonic cultures and biofilm were subjected to successive applications of Photodithazine-mediated (25 mg/L) LED-associated aPDT (660 nm, 34 mW/cm2). Plating was performed on Sabouraud Dextrose Agar supplemented or not with fluconazole to recover colony-forming units per milliliter (CFU/mL). Surviving cells were recovered, recultivated, and again exposed to the treatment. The treatments were performed until not enough colonies were available for recultivation and continuation of the protocol. The complete inactivation of the fungus was obtained after three and five applications for planktonic culture and biofilm, respectively. A reduction of 6.3 log10 was observed after third applications in the planktonic cultures grown on medium without fluconazole, while there was a 7 log10 reduction of these cultures grown on fluconazole medium. However, a reduction of 6.1 log10 occurred for biofilms after fifth applications for cultures grown on medium without fluconazole, while a reduction of 6.7 log10 was observed for cultures grown on medium with the antifungal. Thus, aPDT was potentiated by fluconazole. C. albicans in planktonic and biofilm cultures are susceptible to successive applications of PDZ-mediated aPDT, and tolerance to aPDT is higher in the biofilm.