Antimicrobial photodynamic therapy mediated by phenothiazine photosensitizers against Candida albicans and Candida auris: a systematic review.

Fungal infections caused by Candida albicans and Candida auris represent an increasing clinical challenge, particularly due to biofilm formation and rising antifungal resistance. Antimicrobial photodynamic therapy (aPDT) has emerged as a potential alternative strategy, with phenothiazine-based photosensitizers being among the most extensively investigated compounds. This systematic review aimed to evaluate the application of phenothiazine-mediated aPDT in in vitro studies against C. albicans and C. auris. A comprehensive search was conducted in PubMed, Embase, and Scopus, including studies published within the last 10 years. Forty in vitro studies met the eligibility criteria and were synthesized descriptively due to substantial methodological heterogeneity. Overall, aPDT was associated with reductions in fungal viability, with generally greater effects reported in planktonic models compared with biofilms. Methylene blue was the most frequently investigated photosensitizer, applied across a broad range of concentrations and dosimetric parameters, resulting in variable antifungal responses. Other phenothiazine derivatives, including toluidine blue O, dimethyl methylene blue, new methylene blue, and S137, were also associated with antifungal activity under specific experimental conditions but remain comparatively underexplored. Studies involving C. auris were less frequent and suggested lower susceptibility compared with C. albicans, particularly in biofilm models. Given the substantial variability in experimental protocols, especially regarding photosensitizer concentration, light parameters, and biofilm maturation, the findings should be interpreted with caution and limit direct comparison across studies. These findings support the antifungal potential of phenothiazine-mediated aPDT while emphasizing the need for methodological standardization and expanded investigation of C. auris.