Resistance of Aspergillus fumigatus to Micafungin is Increased by Exogenous β-glucan.

Aspergillus species are ubiquitous in the environment and Aspergillus fumigatus can cause life-threatening infections in immunocompromised patients. β-1,3-/1,6-glucan is a major fungal cell wall polysaccharide that has various biological effects on the infected host, but little is known about the influence of β-glucan on the fungus itself. In a previous study, we demonstrated that the cell wall β-glucan content could be increased in Aspergillus spp. by addition of β-glucan to the culture medium. In this study, we investigated the influence of β-glucan on the susceptibility of A. fumigatus to antifungal agents. A. fumigatus was cultured in the presence or absence of β-glucan for antifungal susceptibility testing based on changes of the growth rate and morphology. Susceptibility to micafungin, a β-glucan synthase inhibitor, was about 10-fold lower when β-glucan was added to the culture medium. On the other hand, susceptibility to amphotericin B and voriconazole was similar in either the presence or absence of β-glucan. These results strongly suggest that β-glucan has an important physiological role in Aspergillus spp.