Evaluation of pathogenicity of Exophiala dermatitidis Melanin in Galleria mellonella infection model

Objective To evaluate the pathogenicity of Exophiala dermatitidis melanin in Galleria mellonella infection model. Methods Melanin of albino strain of Exophiala dermatitidis was restored by co-culture with E. dermatitidis (mel3). The G. mellonella were infected with albino, melanized strtain, and melanin restored albino strain. Survival rate, macromorphological and histopathological changes of larvae were observed under the optimal infection concentration. Results The melanin production was restored in albino strain of Exophiala dermatitidis, and conidia at a concentration of 1×107/mL was the optimal infection concentration. At the end of observation, the albino strain displayed lower survival rate compared to both the melanized stain (χ2=6.11，P=0.013) and melanin restored albino strain (χ2=6.37, P=0.010). However, the survival rates did not differ significantly between melanized and melanin restored albino strain (χ2=0.01，P=0.940). Histopathological examination revealed that the melanized strain and melanin restored albino strain attracted aggregation of more Galleria mellonella hemocytes, forming larger infectious nodules in comparison to albino strains. Conclusions In the infection model of Galleria mellonella, the albino strain shows stronger pathogenicity than the melanized strain. Restoration of melanin of albino strain can reverse the pathogenicity.