Antibiofilm activity of antifungal drugs, including the novel drug olorofim, against Lomentospora prolificans

Objectives: Patients with immunodeficiency or cystic fibrosis frequently suffer from respiratory fungal infections. In particular, biofilm-associated fungi cause refractory infection manifestations, linked to increased resistance to anti-infective agents. One emerging filamentous fungus is Lomentospora prolificans. Here, the biofilm-formation capabilities of L. prolificans isolates were investigated and the susceptibility of biofilms to various antifungal agents was analysed. Methods: Biofilm formation of L. prolificans (n = 11) was estimated by crystal violet stain and antibiofilm activity was additionally determined via detection of metabolically active biofilm using an XTT assay. Amphotericin B, micafungin, voriconazole and olorofim were compared with regard to their antibiofilm effects when added prior to adhesion, after adhesion and on mature and preformed fungal biofilms. Imaging via confocal laser scanning microscopy was carried out to demonstrate the effect of drug treatment on the fungal biofilm. Results: Antibiofilm activities of the tested antifungal agents were shown to be most effective on adherent cells whilst mature biofilm was the most resistant. The most promising antibiofilm effects were detected with voriconazole and olorofim. Olorofim showed an average minimum biofilm eradication concentration (MBEC) of 0.06 mg/L, when added prior to and after adhesion. The MBECs of voriconazole were <= 4 mg/L. On mature biofilm the MBECs of olorofim and voriconazole were higher than the previously determined MICs against planktonic cultures. In contrast, amphotericin B and especially micafungin did not exhibit sufficient antibiofilm activity against L. prolificans. Conclusions: To our knowledge, this is the first study demonstrating the antibiofilm potential of olorofim against the human pathogenic fungus L. prolificans.