Methylene Blue-Loaded Liposomal Nanocarriers Enhance the Efficacy of Photodynamic Therapy against Candida auris Biofilm.

Candida auris poses a significant healthcare challenge, particularly within immunosuppressed patients. This pathogen can colonize the skin and develop biofilms associated with increased antifungal drug resistance that are difficult to treat with a limited antifungal repertoire. Some adjuvant treatments have been investigated, such as photodynamic therapy (PDT), which employs a photosensitizer (PS) irradiated by light. However, most PSs available suffer from poor biofilm penetration. In this in vitro study, a nanocarrier system was proposed as a possible strategy to facilitate the methylene blue (MB) photosensitizer penetration into biofilm and improve PDT action against C. auris. For this, positively (MB-P) and negatively (MB-N) charged liposomes encapsulating MB were successfully fabricated. In the PDT results, both liposome formulations eradicated planktonic cells of C. auris at minimum fungicidal concentrations (MFC) equivalent to those of free MB. MB-loaded liposomes showed enhanced penetration within biofilms and reduced C. auris biofilm burden ∼2× more compared to free MB. Additionally, biofilm biomass was reduced up to 37% with MB-loaded liposomes, while free MB only achieved ∼3% reduction. Furthermore, PDT mediated by MB-P or MB-N led to the production of reactive oxygen species (ROS) 2× higher than free MB, leading to greater oxidative damage toward C. auris biofilms. Finally, the biocompatibility of MB-loaded liposomes was examined against mammalian fibroblasts; MB-loaded liposomes maintained ∼80% cell viability compared to ∼58% viability for free MB. Promisingly, MB-P and MB-N liposomes were able to enhance the in vitro activity of PDT on C. auris biofilms, inciting the development of in vivo studies to validate their efficacy and safety.