Rapid identification of candida species by TaqMan PCR

Abstract

Aim—To develop and evaluate a TaqMan™ polymerase chain reaction (PCR) for the rapid identification and speciation of candida species.

Methods—Species specific primer and probe sets were designed for the identification of Candida albicans, C parapsilosis, C tropicalis, C krusei, C kefyr, and C glabrata from clinical isolates in a 5′ exonuclease (TaqMan™) assay. The probes were labelled with three fluorescent dyes to enable differentiation between species when three primer and probe sets were combined in two multiplexes. The specificity of these assays was evaluated against a range of National Collection of Pathogenic Fungi strains, clinical isolates of yeast, bacterial and viral pathogens.

Results—The primer and probe sets have been shown to be 100% specific for their respective species; there was no crossreaction between any set and human DNA, or extracts from other candida species, fungal, bacterial, or viral pathogens tested. Extracts from two clinical isolates, originally identified as C albicans on the basis of germ tube formation, were not amplified by any of the primer and probe sets. These isolates have been putatively re-identified as C dubliniensis after sequencing of the variable internal transcribed spacer region ITS2 and lack of growth at 45°C.

Conclusion—This TaqMan assay provides a rapid alternative to conventional culture based techniques for the identification and speciation of the most frequently isolated candida species. The simple extraction method followed by TaqMan PCR can identify the six species mentioned in four hours.