In-vitro effect of antimicrobial photodynamic therapy with methylene blue in two different genera of dermatophyte fungi

Background and objectives: Antimicrobial photodynamic therapy (aPDT) is a technique that combines the photoactivation properties of an innocuous chromophore or photosensitizer (PS) and light, producing reactive oxygen molecules that trigger cell death processes. In this study the in-vitro application of aPDT to fight fungal infections was investigated using methylene blue (MB) as the PS. Materials and methods: The antimicrobial PDT process was carried out with MB and red laser light (λ = 633 nm) to activate the PS. Testing was performed with suspensions of various species of dermatophyte fungi (Trichophyton mentagrophytes, Microsporum canis and Microsporum gypseum), including a fungus, which to our knowledge, has not been previously studied using this dye (Trichophyton tonsurans). For T. tonsurans further optimization tests were carried out. Results and discussion: The fungicidal effect of MB-aPDT was evident. Microsporum strains were slightly more sensitivity to the treatment than Trichophyton strains. The response of T. tonsurans to aPDT was less than to the other fungi tested under the same conditions, or even with higher fluence. However, repetitive aPDT treatment with very low doses of light can achieve a good effectiveness with this strain effecting total growth inhibition. Light may even disturb fungi growth in some circumstances, especially in strain such as T. tonsurans. Conclusion: This study with Trichophyton and Microsporum strains showed that MB was an effective PS to inhibit fungal growth through aPDT, reaching a total inhibition in most of the fungi tested. It was found that repeated exposure with low-power light within the framework of aPDT treatment can achieve better results than a single exposure at higher power. © 2016 Walter de Gruyter GmbH, Berlin/Boston.