Characterization of biofilms formed by Candida parapsilosis, C. metapsilosis, and C. orthopsilosis.

Infections due to Candida parapsilosis have been associated with the ability of this fungus to form biofilms on indwelling medical devices. Recently, C. parapsilosis isolates were reclassified into 3 genetically non-identical classes: C. parapsilosis, C. orthopsilosis, and C. metapsilosis. Little information is available regarding the ability of these newly reclassified species to form biofilms on biomedical substrates. In this study, we characterized biofilm formation by 10 clinical isolates each of C. parapsilosis, C. orthopsilosis, and C. metapsilosis. Biofilms were allowed to form on silicone elastomer discs to early (6h) or mature (48 h) phases and quantified by tetrazolium (XTT) and dry weight assays. Surface topography and three-dimensional architecture of the biofilms were visualized using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), respectively. Metabolic activity assay revealed strain-dependent biofilm forming ability of the 3 species tested, while biomass determination revealed that all 3 species formed equivalent biofilms (P>0.05 for all comparisons). SEM analyses of representative isolates of these species showed biofilms with clusters of yeast cells adherent to the catheter surface. Additionally, confocal microscopy analyses showed the presence of cells embedded in biofilms ranging in thickness between 62 and 85 microm. These results demonstrate that similar to C. parapsilosis, the 2 newly identified Candida species (C. orthopsilosis and C. metapsilosis) were able to form biofilms.

Parenteral lipid emulsion induces germination of Candida albicans and increases biofilm formation on medical catheter surfaces.

BACKGROUND: The administration of parenteral nutrition, including lipid emulsion (LE), to patients via medical catheters is an unexplained risk factor for the development of candidemia. Germination and biofilm formation are recognized virulence determinants of Candida albicans. No studies have addressed the effect of LE on candidal biofilm production. In this study, we investigated the effect of LE on candidal germination and its ability to form biofilm on medical catheter material. METHODS: C. albicans strain SC-5314 was grown in standard growth medium in the presence or absence a commercially available LE. Biofilms grown on silicone-elastomer catheter discs in these media were compared for mass by dry weight measurements. Biofilm morphology was analyzed by scanning electron microscopy and confocal laser microscopy. The effect of LE on C. albicans germination and growth was evaluated microscopically and by determination of colony-forming units, respectively. RESULTS: Addition of LE to standard growth medium increased C. albicans biofilm production and resulted in observed changes in biofilm morphology and architecture. Furthermore, LE induced germination and supported the growth of C. albicans. CONCLUSIONS: LE-inducible candidal virulence determinants, such as germination and enhanced biofilm production, may help to explain the increased risk of candidemia in patients receiving LE via medical catheters.