Impact of biofilm formation and azoles' susceptibility in Scedosporium/Lomentospora species using an in vitro model that mimics the cystic fibrosis patients' airway environment.

BACKGROUND

Scedosporium species are the second most isolated filamentous fungi from cystic fibrosis (CF) patients; however, little is known about their virulence aspects in a CF environment. In this context, the current study aimed to evaluate the (i) antifungal susceptibility profiles, (ii) ability to form biofilm and (iii) impact of biofilm formation on the susceptibility to azoles in 21 clinical isolates of Scedosporium recovered from CF patients.

METHODS

Scedosporium apiospermum (n=6), S. aurantiacum (n=6), S. minutisporum (n=3) and Lomentospora prolificans (n=6) were firstly used to compare the antifungal susceptibility profile using a standard culture broth (RPMI-1640) and a mucin (M)-containing synthetic CF sputum medium (SCFM). The ability to form biofilms was investigated in polystyrene microtiter plates containing Sabouraud-dextrose (a classical medium), SCFM and SCFM+M. Mature biofilms were tested for their susceptibility to azoles by microdilution assay.

RESULTS

Our results showed that the minimum inhibitory concentrations (MICs) for planktonic conidia ranged from 0.25 to >16.0 mg/L for voriconazole and 1.0 to >16.0 mg/L for posaconazole. Overall, the MICs for azoles increased from 2- to 8-folds when the susceptibility tests were performed using SCFM+M compared to RPMI-1640. All fungi formed robust biofilms on polystyrene surface at 72 h, with a significant increase in the MICs (ranging from 128- to 1024-times) against both azoles compared to the planktonic cells.

CONCLUSION

These findings confirm the challenge of antifungal treatment of CF patients infected with Scedosporium/Lomentospora and also demonstrated a strong biofilm formation, with extensive increase in antifungal resistance, triggered underconditions mimicking the CF patient airway.