Fibronectin recognition by the emerging multidrug-resistant opportunistic fungal pathogen Candida haemulonii

The multidrug-resistant pathogen Candida haemulonii (Candidozyma haemuli) can cause superficial and systemic infections in vulnerable individuals. The ability of C. haemulonii to interact with extracellular matrix (ECM) components remains largely unexplored. Herein, we investigated C. haemulonii's capacity to bind to fibronectin and assessed how this ECM protein influences fungal adhesion and biofilm development. The results revealed that C. haemulonii yeasts can recognize and interact with soluble fibronectin in a dose-dependent and isolate-specific manner, as demonstrated by flow cytometry. Confocal microscopy confirmed that fibronectin-binding molecules are primarily localized at the periphery of the yeasts, indicating that the binding sites reside on the cell surface. Additionally, C. haemulonii exhibited significantly greater adhesion to polystyrene surface coated with immobilized fibronectin (48.8 ± 5.1 yeasts/microscopic field) compared to either uncoated (28.4 ± 6.5) or albumin-coated (28.7 ± 5.3) surfaces. Fungal biofilm formation was significantly reduced on fibronectin-coated surface in comparison to uncoated control, with both biomass and ECM production decreasing by about 50%, as evaluated by crystal violet and safranin staining, respectively. Western blot analysis revealed that C. haemulonii cells degraded fibronectin during biofilm development. Notably, cell-free biofilm supernatant was capable of cleaving soluble fibronectin; this degradation was partially inhibited by PMSF, indicating the involvement of serine proteases in this process. Corroborating this finding, zymography revealed two serine proteases (50 and 60 kDa) capable of degrading immobilized fibronectin. Collectively, the results demonstrate that C. haemulonii possesses fibronectin-binding molecules that contribute to adhesion and play a critical role in the early stages of its pathogenic process.