Comparative pathogenicity of opportunistic black yeasts in Aureobasidium.

Aureobasidium pullulans and A. melanogenum are black-yeast-like surface colonisers and are commonly encountered as contaminants in the hospital. The species are able to produce melanin which play a role in protection against environmental stress and irradiation. Aureobasidium melanogenum shows higher frequency in opportunistic infections compared to A. pullulans. Comparative pathogenicity of opportunistic black yeasts between Aureobasidium pullulans and A. melanogenum to explain the observed differences in frequency in infection. Degrees of melanisation and thermotolerance were measured, and virulence of strains from different sources was examined in Galleria mellonela and murine infection models. Aureobasidium melanogenum responds with increased melanisation to temperature stress and generally survives at 37°C, A. pullulans on average scored less on these parameters. In the murine model, differences between species were not significant, but the melanised A. melanogenum group showed the highest virulence. This result was not reproducible in Galleria mellonella larvae at 25°C. The A. melanogenum black group showed higher pathogenicity in murine model, indicating that the combination of melanisation and thermotolerance rather than species affiliation is instrumental. Galleria larvae did not survive very well at 37°C, and hence, this model is judged insufficient to detect the small virulence differences observed in Aureobasidium.