Rapid molecular differentiation and genotypic heterogeneity among Candida parapsilosis and Candida orthopsilosis strains isolated from clinical specimens in Kuwait

Recent molecular studies have led to the recognition of three distinct species within the Candida parapsilosis complex, namely Candida parapsilosis, Candida orthopsilosis and Candida metapsilosis. As currently available yeast identification systems fail to differentiate these species, there is a paucity of information on their occurrence in different geographical regions. This study describes a simple PCR-based protocol for rapid discrimination among C. parapsilosis, C. orthopsilosis and C. metapsilosis strains by using primers derived from unique sequences within the internally transcribed spacer 1 (ITS1)-5.8 rRNA-ITS2 region. Retrospective analysis of 114 C. parapsilosis-complex isolates recovered from clinical specimens in Kuwait identified 109 as C. parapsilosis, five as C. orthopsilosis and none as C. metapsilosis. The results were further validated by PCR-RFLP patterns of the secondary alcohol dehydrogenase gene fragment. DNA sequencing of the ITS region and the D1/D2 regions of the 28S rRNA gene confirmed the species-specific identification of all five C. orthopsilosis strains. The amplicon length of the intergenic spacer between the 28S and 5S rRNA genes (IGS1) was also species-specific, and PCR-RFLP analyses of the IGS1 region identified two distinct genotypes among the five C. orthopsilosis strains, which corresponded with the ITS region sequence data. The three bloodstream C. orthopsilosis strains were confined to a single genotype. Among 81 randomly selected C. parapsilosis strains, two genotypes were detected by IGS1 region analyses, indicating limited genotypic heterogeneity among C. parapsilosis sensu stricto strains. As far as is known, this is the first report on the identification of C. orthopsilosis from a bloodstream infection in the Arabian Gulf region.