Aspergillus fumigatus is associated with many human health conditions . It is the most common cause of invasive aspergillosis, an opportunistic infection whose incidence increases in immunocompromised patients . Aspergillosis is also prevalent in animals, such as dogs and birds [3,4]. A. fumigatus is responsible for more human and animal diseases than other moulds even though their conidia are usually outnumbered by spores of other mould species in inhaled air, suggesting that A. fumigatus has special properties that enable it to colonize the lungs of its hosts . Most studies with A. fumigatus have focused on the interactions of the fungus with alveolar macrophages [6,7] or with cell line A549 from pneumocytes [8,9]. However, the first tissue usually encountered by the inhaled conidia is the airway epithelium, and it is frequently damaged in patients at risk for invasive aspergillosis . We previously studied the interactions between A. fumigatus and the respiratory epithelium using human nasal epithelium cell (HNEC) cultures [11,12]. After one week of culture, the HNEC are organized in a pseudostratified epithelium with mucus and ciliated cells, very similar to the in vivo airway epithelium .
We found that a filtrate from A. fumigatus cultures has specific electrophysiological effects on HNEC compared with one from fungi not responsible for invasive infection . Effects included a decrease in transepithelial electrical resistance and polarization of the epithelium. These changes to the epithelium properties could play a role in the ability of A. fumigatus to colonize the respiratory tract. In the present study, in order to identify which compounds were responsible for these changes, we used high-performance liquid chromatography with diode-array detection (HPLC-DAD) to fractionate the filtrate of A. fumigatus culture. Thus, we identified verruculogen as the toxin responsible for the toxic effects observed in the epithelial cell model. To determine whether verruculogen was associated with conidia upon its first contact with epithelial cells, the presence of verruculogen was specifically monitored in conidial extracts by mass spectrometry analysis. Moreover, since every isolate of A. fumigatus is potentially responsible for invasive aspergillosis (as previously shown using polymorphic microsatellite markers [13,14]), the ability of every isolate to produce verruculogen was a prerequisite for involving verruculogen as a pathogenic factor. The production of verruculogen was therefore verified in a collection of 67 human, animal, plant and environmental A. fumigatus isolates.