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Updated: Jun 6, 2026
LED-Based In Vitro Screening for Assessing Photoactivable Molecules in Bacterial Photodynamic Inactivation
Published on: January 24, 2025
Cryptococcus gattii: in vitro susceptibility to photodynamic inactivation
Betânia Maria Soares1, Orley Araújo Alves, Marcus Vinícius Lucas Ferreira
1Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. bmsoares@gmail.com
Abstract:
Cryptococus gattii is an emergent primary human pathogen that causes meningismus, papilledema, high intracranial pressure and focal involvement of the central nervous system in immunocompetent hosts. Prolonged antifungal therapy is the conventional treatment, but it is highly toxic, selects for resistant strains, contributes to therapy failure and has a poor prognosis. Photodynamic inactivation (PDI) offers a promising possibility for the alternative treatment of cryptococcosis. The aim of this study was to test the effectiveness of toluidine blue O (TBO) and light-emitting diode (LED) against C. gattii strains with distinct susceptibility profile to antifungal drugs (amphotericin B: 0.015-1.0 μg mL(-1); itraconazole: 0.015-2 μg mL(-1); fluconazole: 4-64 μg mL(-1)). Using 25 μM (6.76 μg mL(-1)) TBO and LED energy density of 54 J cm(-2) these fungal isolates presented variable susceptibility to PDI. The production of reactive oxygen species (ROS)/peroxynitrite was determined, and the catalase and peroxidase activities were measured. After PDI, high amounts of ROS/peroxynitrite are produced and higher catalase and peroxidase activities could be correlated with a lower susceptibility of C. gattii isolates to PDI. These results indicate that PDI could be an alternative to C. gattii growth inhibition, even of isolates less susceptible to classical antifungal drugs, also pointing to mechanisms related to their variable susceptibility behavior.
Insights
Photodynamic inactivation (PDI) using toluidine blue O and LED light shows promise for treating Cryptococcus gattii infections. This method effectively inhibits fungal growth, even in strains resistant to conventional antifungal drugs.
Area of Science:
- * Infectious Diseases
- * Mycology
- * Photomedicine
Background:
- * Cryptococcus gattii is an emerging pathogen causing serious central nervous system infections in immunocompetent individuals.
- * Conventional antifungal therapy for cryptococcosis is toxic, leads to resistance, and has poor outcomes.
- * Photodynamic inactivation (PDI) presents a potential alternative treatment strategy.
Purpose of the Study:
- * To evaluate the efficacy of toluidine blue O (TBO)-mediated PDI against Cryptococcus gattii strains.
- * To assess PDI effectiveness on C. gattii isolates with varying antifungal drug susceptibility.
- * To investigate the role of reactive oxygen species (ROS) and antioxidant enzymes in PDI susceptibility.
Main Methods:
- * Testing the susceptibility of C. gattii isolates to PDI using 25 μM TBO and 54 J cm(-2) LED energy density.
- * Measuring the production of ROS/peroxynitrite post-PDI.
- * Quantifying catalase and peroxidase activities in C. gattii isolates.
Main Results:
- * C. gattii isolates exhibited variable susceptibility to TBO-based PDI.
- * PDI treatment induced significant ROS/peroxynitrite production.
- * Higher catalase and peroxidase activity correlated with lower susceptibility to PDI.
Conclusions:
- * PDI is a viable strategy for inhibiting C. gattii growth, including drug-resistant strains.
- * Antioxidant enzyme activity influences C. gattii susceptibility to PDI.
- * PDI offers a promising alternative to conventional antifungal treatments for cryptococcosis.
