Determinants of virulence in the pathogenic fungi

Hartmannella vermiformis can promote proliferation of Candida spp. in tap-water

Candida yeasts colonize humans' oral cavities as commensals or opportunistic pathogens. They may be isolated from water circulating in dental unit waterlines mixed with saliva traces mainly because of dysfunction of anti-retraction valves. Free-living amoebae (FLA), like Hartmannella vermiformis, are frequently found in aquatic environments and they have also been already isolated from dental unit waterlines. They can be implicated as reservoir for pathogens or directly in infections. This work deals with the survival of three species of Candida (Candida albicans, Candida glabrata and Candida parapsilosis), in co-cultivation with FLA in tap-water. One strain of each Candida species was studied. Microbiological and microscopic approaches were used; amoebae-yeasts co-cultivation assays were performed at different temperatures of incubation. Results have shown that H. vermiformis were able to internalize Candida yeasts and promote their proliferation in tap-water with or without saliva traces (2% v/v). Amoebae interact differently with Candida depending on the temperature used and the studied species of yeasts. In conclusion, this study emphasizes the survival of yeasts and/or FLA in tap-water. The ability of yeasts and amoebae to interact should be taken into account because it could lead to candidiasis infection for the frailest patients after a dental treatment.

Pga26 mediates filamentation and biofilm formation and is required for virulence in Candida albicans

The Candida albicans gene PGA26 encodes a small cell wall protein and is upregulated during de novo wall synthesis in protoplasts. Disruption of PGA26 caused hypersensitivity to cell wall-perturbing compounds (Calcofluor white and Congo red) and to zymolyase, which degrades the cell wall β-1,3-glucan network. However, susceptibility to caspofungin, an inhibitor of β-1,3-glucan synthesis, was decreased. In addition, pga26Δ mutants show increased susceptibility to antifungals (fluconazol, posaconazol or amphotericin B) that target the plasma membrane and have altered sensitivities to environmental (heat, osmotic and oxidative) stresses. Except for a threefold increase in β-1,6-glucan and a slightly widened outer mannoprotein layer, the cell wall composition and structure was largely unaltered. Therefore, Pga26 is important for proper cell wall integrity, but does not seem to be directly involved in the synthesis of cell wall components. Deletion of PGA26 further leads to hyperfilamentation, increased biofilm formation and reduced virulence in a mouse model of disseminated candidiasis. We propose that deletion of PGA26 may cause an imbalance in the morphological switching ability of Candida, leading to attenuated dissemination and infection.