Biofilm Formation by Pseudallescheria/Scedosporium Species: A Comparative Study

Abstract

<i>Pseudallescheria/Scedosporium</i> species are medically important fungi that are present in soil and human impacted areas and capable of causing a wide spectrum of diseases in humans. Although little is known about their pathogenesis, their growth process and infection routes are very similar to those of <i>Aspergillus</i> species, which grow as biofilms in invasive infections. All nine strains tested here displayed the ability to grow as biofilms <i>in vitro</i> and to produce a dense network of interconnected hyphae on both polystyrene and the surfaces of central venous catheters, but with different characteristics. <i>Scedosporium boydii</i> and <i>S. aurantiacum</i> clinical isolates were able to form biofilms faster than the corresponding environmental strains, as evidenced in kinetic assays for <i>S. boydii</i> and CLSM for <i>S. aurantiacum</i>. Biofilms formed by <i>Pseudallescheria/Scedosporium</i> species had significantly higher resistance to the class of antifungal azole than was observed in planktonic cells, indicating a protective role for this structure. In addition, the clinical <i>S. aurantiacum</i> isolate that formed the most robust biofilms was also more virulent in a larvae <i>Galleria mellonella</i> infection model, suggesting that the ability to form biofilms enhances virulence in <i>Pseudallescheria/Scedosporium</i> species.