Methylene Blue-Loaded Liposomal Nanocarriers Enhance the Efficacy of Photodynamic Therapy against <i>Candida auris</i> Biofilm

<i>Candida auris</i> 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 <i>C. auris</i>. 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 <i>C. auris</i> at minimum fungicidal concentrations (MFC) equivalent to those of free MB. MB-loaded liposomes showed enhanced penetration within biofilms and reduced <i>C. auris</i> 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 <i>C. auris</i> 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 <i>C. auris</i> biofilms, inciting the development of in vivo studies to validate their efficacy and safety.