Separation of phenotypically indistinguishable Candida species, C. orthopsilosis, C. metapsilosis and C. parapsilosis, by capillary electromigration techniques

At the current state of laboratory diagnostics, methods for fast identification of phenotypically indistinguishable species are difficult or inaccurate. An example is represented by Candida parapsilosis, which is the second most common yeast species isolated from bloodstream infections. C. parapsilosis comprises a complex of three genetically distinct groups. Genotypes II and III have been designated as the separate species Candida orthopsilosis and Candida metapsilosis, phenotypically indistinguishable. The considerable genetic variability of these newly described yeasts species has caused difficulties in the development of molecular techniques for their precise identification. Similarly, the detection of biofilm formation, which is considered as an important yeast virulence factor, is accompanied by difficulties. In this study we optimize the first precise and reproducible method for the separation and possible identification of C. orthopsilosis, C. metapsilosis and C. parapsilosis as well as the detection of their ability to form biofilm. The method is based on capillary isoelectric focusing and capillary electrophoresis with UV detection. In capillary isoelectric focusing, very narrow pH gradients were established. With such gradients, differences in isoelectric points of biofilm-negative and biofilm-positive species calculated from the migration times of the selected pI markers were below 0.03 pI units. In the capillary zone electrophoresis narrow zones of the cells of Candida species were detected with sufficient resolution. The values of the isoelectric point and the migration velocities of the examined species were independent on the origin of the tested strains. Capillary isoelectric focusing was examined also for the separation and detection of the cultivated biofilm-negative C. parapsilosis in the blood serum.