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Updated: Jun 20, 2026
Rose Bengal-Mediated Photodynamic Therapy to Inhibit Candida albicans
Published on: March 24, 2022
New Insights in Phenothiazinium-Mediated Photodynamic Inactivation of Candida Auris
Abdênego R Silva1, Fernanda V Cabral1, Camila R Silva1
1Center for Lasers and Applications, Nuclear and Energy Research Institute (IPEN-CNEN), São Paulo 05508-000, SP, Brazil.
Abstract:
In recent years, Candida auris has emerged as a hazardous hospital-acquired pathogen. Its resistance to antifungal treatments makes it challenging, requiring new approaches to manage it effectively. Herein, we aimed to assess the impact of photodynamic inactivation mediated by methylene blue (MB-PDI) or 1,9-dimethyl MB (DMMB-PDI) combined with a red LED against C. auris. To evaluate the photoinactivation of yeasts, we quantified colony-forming units and monitored ROS production. To gain some insights into the differences between MB and DMMB, we assessed lipid peroxidation (LPO) and mitochondrial membrane potential (ΔΨm). After, we verified the effectiveness of DMMB against biofilms by measuring metabolic activity and biomass, and the structures were analyzed through scanning electron microscopy and optical coherence tomography. We also evaluated the cytotoxicity in mammalian cells. DMMB-PDI successfully eradicated C. auris yeasts at 3 μM regardless of the light dose. In contrast, MB (100 μM) killed cells only when exposed to the highest dose of light. DMMB-PDI promoted higher ROS, LPO and ΔΨm levels than those of MB. Furthermore, DMMB-PDI was able to inhibit biofilm formation and destroy mature biofilms, with no observed toxicity in fibroblasts. We conclude that DMMB-PDI holds great potential to combat the global threat posed by C. auris.
Insights
Photodynamic inactivation using 1,9-dimethyl methylene blue (DMMB-PDI) effectively eradicated Candida auris yeasts and biofilms. This novel approach shows promise for combating this hazardous, drug-resistant hospital-acquired pathogen.
Area of Science:
- Antimicrobial photodynamic therapy
- Emerging infectious diseases
- Medical mycology
Background:
- Candida auris is a hazardous hospital-acquired pathogen known for its antifungal resistance.
- Effective management strategies for Candida auris infections are urgently needed.
- Photodynamic inactivation (PDI) offers a potential alternative therapeutic approach.
Purpose of the Study:
- To evaluate the efficacy of photodynamic inactivation using methylene blue (MB-PDI) or 1,9-dimethyl MB (DMMB-PDI) against Candida auris.
- To compare the mechanisms of action between MB-PDI and DMMB-PDI.
- To assess the effectiveness of DMMB-PDI against Candida auris biofilms and its cytotoxicity.
Main Methods:
- Quantification of colony-forming units and reactive oxygen species (ROS) production.
- Assessment of lipid peroxidation (LPO) and mitochondrial membrane potential (ΔΨm).
- Biofilm analysis using metabolic activity, biomass, scanning electron microscopy, and optical coherence tomography; cytotoxicity assays in mammalian cells.
Main Results:
- DMMB-PDI eradicated Candida auris yeasts at 3 μM, irrespective of light dose, while MB-PDI required higher concentrations and light doses.
- DMMB-PDI induced significantly higher ROS, LPO, and ΔΨm compared to MB-PDI.
- DMMB-PDI inhibited biofilm formation, eradicated mature biofilms, and demonstrated no cytotoxicity in fibroblasts.
Conclusions:
- 1,9-dimethyl MB-mediated photodynamic inactivation (DMMB-PDI) is a highly effective strategy against Candida auris yeasts and biofilms.
- DMMB-PDI exhibits a superior mechanism of action involving increased ROS production, LPO, and mitochondrial disruption.
- DMMB-PDI presents a promising, non-toxic therapeutic candidate to address the global threat of Candida auris infections.
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