In vitro activity of aminosterols against yeasts involved in blood stream infections

Squalamine and other aminosterols have demonstrated interesting antimicrobial activities against clinical bacterial isolates and a limited number of reference yeast strains. We aimed to test whether squalamine and a synthetic aminosterol derivative (ASD) display any in vitro activity comparable to currently available systemic antifungals, an acceptable safety index, as well as to provide insights into their mechanism of action. The minimum inhibitory concentrations (MICs) of squalamine, ASD and available antifungals were determined against 21 yeast isolates that were recovered from cases of fungemia. Remarkably, homogeneous MICs ranging from 8-16 mg/L and from 1-2 mg/L were noted for squalamine and ASD, respectively, as opposes the heterogeneous in vitro activity of available systemic antifungals. Aminosterols induced haemolysis, a surrogate for toxic effects to mammalian cells, at concentrations high above their MICs. In time-kill studies, killing was as fast with ASD as with amphotericin B. Both aminosterols induced a time-dependent disruption of yeast membrane, as evidenced by gradual increase of ATP efflux. In conclusion, our preliminary data indicate that aminosterols have the potential to be further developed as antifungals. Additional work is warranted to assess their toxicity and activity in experimental models.