Photoinactivation of Candida albicans using methylene blue alone or in combination with chlorhexidine

Antonio Rezusta, Vanesa Pérez Laguna, Luna Pérez-Artiaga, Verónica Lampaya, Yolanda Gilaberte, Lorena Fernandez Lacasta, Maria Carmen Alejandre, Maria Jose Revillo


Background: Candida albicans is a yeast frequently found in skin and mucous membranes that can be an important pathogen commonly involved in infections. In addition, antifungal resistance is increasing and the development of new treatment strategies is required. Antimicrobial photodynamic therapy (aPDT), based on the application of a photosensitizer, like Methylene Blue (MB), activated by visible light to generate reactive oxygen species that are cytotoxic to microorganisms, could be an alternative treatment. The aim of this study was to compare the efficacy of aPDT-MB on C. albicans alone or combined with chlorhexidine that is an effective antiseptic widely used.

Material/methods: C. albicans ATCC 10231 suspensions containing >107 cells/mL were prepared. Different concentrations two-fold serial dilution of MB (from 0.32 μg/ml to 640 μg/ml) alone or combined with 10 μg/mL of chlorhexidine were tested. Irradiation was performed with a red lightemitting diode (LED) lamp (625 nm, 0.007 W/cm2 ) at a fluence of 18 J/cm2 . The resultant suspensions were subcultured onto agar Sabouraud with added chloramphenicol to determine the viable yeasts by colony-forming units counting (CFU/mL). A criterion of 6 log10 unit decrease from the starting inoculum was adopted to define fungicidal activity. Dark and irradiated controls, with and without MB or chlorhexidine were included.

Results: A reduction of 6 log10 CFU/mL was reached with 160-320 μg/mL of MB, diminishing the concentration to 10-20 µg/mL adding 10 μg/ml of chlorhexidine. The same amount of chlorhexidine itself reached only 1-1.5 log10 reduction (Graphic 1).

Conclusions: In vitro PDT-MB has a significant fungicidal effect on C. albicans and seems to have synergic effect with chlorhexidine against this yeast, which is very convenient to translate this therapy into the clinic.

Acknowledgements: This work has been supported by grant CTQ2013-48767-C3-2-R from the Spanish Ministerio de Economía y Competitividad.




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26th European Congress of Clinical Microbiology and Infectious Diseases
    • ECCMID 26th (2016)