Susceptibilities of the dermatophytes Trichophyton mentagrophytes and T. rubrum microconidia to photodynamic antimicrobial chemotherapy with novel phenothiazinium photosensitizers and red light.

Photodynamic antimicrobial chemotherapy (PACT) is a promising alternative to conventional chemotherapy that can be used to treat localized mycosis. The development of PACT depends on identifying effective and selective PS for the different pathogenic species. The in vitro susceptibilities of Trichophyton mentagrophytes and Trichophyton rubrum microconidia to PACT with methylene blue (MB), toluidine blue O (TBO), new methylene blue N (NMBN), and the novel pentacyclic phenothiazinium photosensitizer S137 were investigated. The efficacy of each PS was determined based on its minimal inhibitory concentration (MIC). Additionally, we evaluated the effect of PACT with NMBN and S137 on the survival of the microconidia of both species. S137 showed the lowest MIC. MIC for S137 was 2.5 μM both for T. mentagrophytes and T. rubrum, when a light dose of 5 J cm(-2) was used. PACT with NMBN (10 μM and 20 J cm(-2)) resulted in a reduction of 4 logs in the survival of the T. rubrum and no survivor of T. mentagrophytes was observed. PACT with S137 at 1 μM and 20 J cm(-2) resulted in a reduction of approximately 3 logs in the survival of both species. When a S137 concentration of 10 μM was used, no survivor was observed for both species at all light doses (5, 10 and 20 J cm(-2)).