Multi-probe Real-Time PCR Identification of Four Common Candida Species in Blood Culture Broth

Suporn Foongladda, Nanthanida Mongkol, Pornphan Petlum, Methee Chayakulkeeree

We developed a single-tube real-time polymerase chain reaction (PCR) assay with multiple hybridization probes for detecting Candida albicans, C. tropicalis, C. glabrata, and C. parapsilosis. Primers were designed to amplify 18S rRNA gene of the genus Candida, and DNA probes were designed to hybridize two areas of the amplicons. The amplification curves and specific melting peaks of the probes hybridized with PCR product were used for definite species identifications. The reaction specificity was 100 % when evaluating the assay using DNA samples from 21 isolates of fungal and bacterial species. The assay was further evaluated in 129 fungal blood culture broth samples which were culture positive for fungus. Of the 129 samples, 119 were positively identified as: C. albicans (39), C. tropicalis (30), C. parapsilosis (23), C. glabrata (20), Candida spp. (5), and two samples containing mixed C. glabrata/C. albicans and C. glabrata/C. tropicalis. The five Candida spp. were identified by sequencing analysis as C. krusei, C. dubliniensis, C. aquaetextoris, and two isolates of C. athensensis. Of the ten samples which showed negative PCR results, six were Cryptococcus neoformans, and the others were Trichosporon sp., Rhodotorula sp., Fusarium sp., and Penicillium marneffei. Our findings show that the assay was highly effective in identifying the four medically important Candida species. The results can be available within 3 h after positivity of a blood culture broth sample.