Background: Bacterial biofilms have been implicated in chronic rhinosinusitis (CRS). However, direct evidence in support of fungal biofilms in sinus disease is lacking in the literature. This study was designed to develop and characterize an in vitro Aspergillus fumigatus biofilm model on primary human sinonasal epithelial cell culture.
Methods: Sinonasal biopsy specimens harvested during endoscopic sinus surgery of six CRS patients and three pituitary tumor (control) patients were cultured in Dulbecco's modified Eagle media (DMEM; Invitrogen)/Hams F12 airway media to encourage epithelial cell proliferation. Epithelial cells separated by immunomagnetic beads were seeded in tissue culture-treated Y-shaped microslides. At confluence the primary cultures were inoculated with A. fumigatus spores. Fungus was allowed to germinate and form biofilms under two in vitro conditions: (1) static (no flow through of media) and (2) continuous flow coculture (continuous flow movement of media). At regular intervals cocultures were stained with FUN-1, concanavalin A-alexa fluor 488, and examined by confocal scanning laser microscopy. Comstat software was used to assess biomass and thickness.
Results: A. fumigatus formed three-dimensional biofilm structures with parallel-packed, cross-linked hyphae and channels/passages. Metabolically active hyphae showed orange-red fluorescing intravacuolar structures. Extracellular matrix (ECM) between/around the hyphae fluoresced intense green. A. fumigatus biofilms development occurred in five stages: (1) conidial attachment to epithelial cells, (2) hyphal proliferation, (3) ECM production, (4) hyphal parallel packing and cross-linking, and (5) channel/pores formation. Mature biofilms showed basal conidial, middle hyphal, and superficial ECM layers. Biofilms formed under flow conditions displayed more robust and faster growth kinetics when compared with that under static conditions, with a thick, stocky, wrinkly/undulating hyphal growth and extensive ECM production. The differences in biomass and average thickness of the cocultures under static and flow conditions were statistically significant after similar periods of incubation (p = 0.0002; p < 0.0001, respectively).
Conclusion: To our knowledge, this is the first article of an in vitro model characterizing A. fumigatus biofilm formation using primary human sinonasal epithelium under different growth conditions.