Species of the Metarhizium anisopliae complex with diverse ecological niches display different susceptibilities to antifungal agents

Species of the Metarhizium anisopliae complex are globally ubiquitous soil-inhabiting and predominantly insect-pathogenic fungi. The Metarhizium genus contains species ranging from specialists, such as Metarhizium acridum that only infects acridids, to generalists, such as M. anisopliae, Metarhizium brunneum, and Metarhizium robertsii that infect a broad range of insects and can also colonize plant roots. There is little information available about the susceptibility of Metarhizium species to clinical and non-clinical antifungal agents. We determined the susceptibility of 16 isolates comprising four Metarhizium species with different ecological niches to seven clinical (amphotericin B, ciclopirox olamine, fluconazole, griseofulvin, itraconazole, tebinafine, and voriconazole) and one non-clinical (benomyl) antifungal agents. All isolates of the specialist M. acridum were clearly more susceptible to most antifungals than the isolates of the generalists M. anisopliae sensu lato, M. brunneum, and M. robertsii. All isolates of M. anisopliae, M. brunneum, and M. robertsii were resistant to fluconazole and some were also resistant to amphotericin B. The marked differences in susceptibility between the specialist M. acridum and the generalist Metarhizium species suggest that this characteristic is associated with their different ecological niches, and may assist in devising rational antifungal treatments for the rare cases of mycoses caused by Metarhizium species.