In vitro activity of olorofim against Aspergillus fumigatus sensu lato clinical isolates: activity is retained against isolates showing resistance to azoles and/or amphotericin B

Objectives: New antifungal drugs, such as olorofim, may overcome the problem of resistance in Aspergillus fumigatus. We here report the activity of olorofim against a set of A. fumigatus sensu lato recently collected in Spain.

Methods: A total of 332 A. fumigatus sensu lato clinical isolates collected in a multicentre study conducted in Spain in 2019 and comprising susceptible and resistant isolates to azoles and/or amphotericin B were tested. Isolates distributed among the following species: A. fumigatus sensu stricto (n = 312), Aspergillus lentulus (n = 6), Aspergillus fumigatiaffinis (n = 5), Neosartorya tsurutae (n = 3), Neosartorya udagawae (n = 3), Aspergillus novofumigatus (n = 2), and Aspergillus thermomutatus (n = 1). Azole resistance was found in 44 A. fumigatus sensu stricto isolates that harboured the following cyp51A gene substitutions: TR₃₄-L98H (n = 24), G54 (n = 5), TR₄₆/Y121F/T289A (n = 1), other mutations (n = 4), and gene wild type (n = 10). Isolates were tested for antifungal susceptibility to olorofim using European Committee on Antimicrobial Susceptibility Testing (EUCAST) E.Def. 9.4 methodology.

Results: Olorofim minimum inhibitory concentrations against A. fumigatus sensu stricto isolates ranged from 0.008 to 0.125 mg/L and in vitro activity of the drug was not impacted by the presence of azole/amphotericin B resistance. Azole resistance and amphotericin B resistance was found in 18 and 13 cryptic species isolates, respectively. Olorofim showed high in vitro activity against cryptic species isolates and minimum inhibitory concentrations ranged from 0.004 to 0.016 mg/L, regardless of the presence of resistance to other drugs.

Discussion: Olorofim showed in vitro activity against both A. fumigatus sensu stricto and cryptic species clinical isolates and was active against isolates showing resistance to azoles and/or amphotericin B.