Ricerc@Sapienza

Objective: The main objectives of this work was to evaluate “in vitro” the hydrophobicity levels, the adherence on a plastic
surface and the biofilm formation of 51 clinical isolates of Malassezia spp.
Methods: 32 M. furfur, 10 M. sympodialis, 5 M. globosa, 2 M. slooffiae, 1 M. restricta and 1 M. pachydermatis, were all
clinical isolates tested. M. furfur and M. sympodialis references strains were also included. In order to examine the adherence
capacity to plastic surface, the yeasts were grown for 72 h at 32◦C in Leeming-Notman modified broth, washed twice with sterile
PB and then resuspended at 37◦C in RPMI 1640 modified for Malassezia plus 10% FBS at 7.5 × 102 cells/ml. After incubation for
3 h at 37◦C in six-well polystyrene plates followed by extensive washing, 1 ml of Leeming-Notman Agar medium modified was
poured into each well and let solidify. After incubation for 72 h at 37◦C, colonies were counted and the results were expressed as
a percentage of the inoculum size. Cellular surface hydrophobicity (CSH) levels were determined by two-phase system. The biofilm
formation was determined by tetrazolium salt (XTT) reduction assay.
Results: All isolates of Malassezia spp. were hydrophobic, adherent and producers of biofilm on abiotic surfaces with different
capacity. In particular, hydrophobicity was variable and ranged from 24 ± 0.1% for M. pachydermatis to 69.50 ± 14.6% for M.
restricta. Similar values were observed for M. furfur and M. globosa. Adherences values also display variability, with ranges between
8.4 ± 1.1% for M. pachydermatis to 85.00 ± 2.3% for M. restricta. High values of adherence were obtained for M. globosa (65.22
± 3.5). In addition, the no lipid-dependent yeast M. pachydermatis showed low values of adherence and hydrophobicity respect to
the other Malassezia species. All Malassezia spp. were able to form biofilm on surface, ranged from 0.179 ± 0.13% for M. slooffiae
to 0. 574 ± 0.20% for M. furfur. Except for M. pachydermatis, similar values were reported for the other Malassezia species tested.
Conclusion: Our results suggest that all clinical isolates of Malassezia spp. were hydrophobic. Since the hydrophobicity is an
important factor to adherence, varying degrees of success on abiotic surface were obtained. These characteristics are also involved
in the high ability to form biofilm observed in this study.
These important virulence factors could be responsible of this yeast changing from a commensal to a pathogenic status. The
revision of the genus Malassezia has opened up new questions about the pathogenicity of Malassezia species.