Rapid electrochemical identification of pathogenic Candida species

1 Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK 2 Department of Chemistry, University of Bath, Bath BA2 7AY, UK 3 Atlas Genetics Ltd, White Horse Industrial Park, Trowbridge, UK Correspondence Alan Wheals bssaew{at}bath.ac.uk Received January 6, 2009 Accepted June 2, 2009 This study describes the development of a novel assay to detect fungal DNA and identify the most clinically relevant invasive human pathogenic fungi to the species level using oligonucleotide probes, labelled with electrochemically active groups, and solid-state electrodes. A panfungal probe designed against the 18S rRNA gene region, capable of detecting all fungal pathogens tested, and species-specific probes, designed against the ITS2 region for detection of the five Candida species most commonly encountered in the clinical setting ( Candida albicans , Candida glabrata , Candida parapsilosis species complex, Candida krusei and Candida tropicalis ), are described. When tested with PCR-amplified DNA from both type and clinical strains of the relevant species, the probes were able to positively identify the relevant fungi, indicated by production of a current significantly elevated above the background reading. No cross-reactivity was observed with any of the species-specific probes when compared with nine non-target Candida species or in the presence of human DNA equivalent to an equal number of ITS2 targets. The panfungal probe gave results that were similarly positive against 15 other fungal species and also did not cross-react with human DNA. The limit of detection of the assay was shown to be approximately 1 genome equivalent for all probes using extracted genomic DNA.