Effect of melanin biosynthesis inhibition in the antifungal susceptibility of chromoblastomycosis agents.

Chromoblastomycosis (CBM) is a chronic subcutaneous infection caused by genera of melanized fungi: Fonsecaea, Cladophialophora, Phialophora, Exophiala and Rhinocladiella Melanin is a virulence factor known to influence antifungal susceptibility. A specific inhibitor of melanin biosynthesis is tricyclazole. The aim of this study was to evaluate the effect of melanin inhibition on antifungal susceptibility of chromoblastomycosis agents and describe the susceptibility profile of some unusual CBM agents. Seventy-six clinical isolates, representing 13 species of the five main CBM agents genera, were studied. The antifungal susceptibility was performed according to the M38-A2 protocol of CLSI. In the melanin inhibition test, 16 mg/L of tricyclazole was added to the medium used in the inoculum preparation and the susceptibility assay. CBM agents were less susceptible to amphotericin B in comparison with azoles and terbinafine. The unusual species showed similar susceptibilities profiles to those of other species of the same genera. With tricyclazole exposition, MICs of terbinafine, posaconazole and itraconazole for Fonsecaea spp. significantly decreased (p<0,05). For Phialophora spp., this reduction was significative for posaconazole and itraconazole. For the other genera, there was a reduction in MICs of terbinafine and itraconazole, however, the statistical tests were not significant. Melanin inhibition can increase the antifungal susceptibility of most CBM agents to itraconazole and terbinafine, the main used drugs in the disease treatment. This increased susceptibility may open up new possibilities for therapy in refractory cases of CBM and/or caused by resistant fungal strains. Further studies are needed to confirm the same results in vivo.