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Journal of Clinical Microbiology, September 2007, p. 2872-2880, Vol. 45, No. 9
0095-1137/07/$08.00+0     doi:10.1128/JCM.00687-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Reverse Line Blot Hybridization Assay for Identification of Medically Important Fungi from Culture and Clinical Specimens

Xianyu Zeng,^1,2, Fanrong Kong,^1, Catriona Halliday,¹ Sharon Chen,¹ Anna Lau,¹ Geoffrey Playford,^3,4 and Tania C. Sorrell^1,3*

Centre for Infectious Diseases and Microbiology-Public Health (CIDM-PH), Institute of Clinical Pathology and Medical Research, Westmead Hospital, Westmead, Australia,¹ Research Laboratory for Infectious Skin Diseases, Department of Dermatology, Wuhan First Hospital, Wuhan, Hubei Province, People's Republic of China,² Westmead Millennium Institute and Department of Medicine, University of Sydney, Sydney, Australia,³ Infection Management Services, Princess Alexandra Hospital, Brisbane, Australia⁴

Received 28 March 2007/ Returned for modification 7 June 2007/ Accepted 5 July 2007

We evaluated a combined panfungal PCR-reverse line blot (RLB) hybridization assay based on internal transcribed spacer 1 (ITS1) and ITS2 region polymorphisms to identify 159 Candida, Cryptococcus neoformans, and Aspergillus isolates (22 species). Its utility to identify fungal pathogens directly from 27 clinical specimens was also determined. ITS sequence analysis was performed to resolve discrepant identifications or where no RLB result was obtained. Species-specific ITS2- and ITS1-based probes correctly identified 155 of 159 isolates (98%) and 149 (93.7%) isolates, respectively. All strains were unambiguously differentiated with the exception of cross-reactivity between the Candida norvegensis probe and Candida haemulonii DNA product. Species identification of the pathogen was made for all 21 specimens (sensitivity of 100%) where species-specific probes were included in the RLB; however, there was no ITS2 probe-based hybridization signal for two specimens. Results were concordant with the culture results for 18 (85.7%) specimens. The assay was able to provide species identification in the absence of a culture result (two specimens) and to detect mixed infection (one specimen). The results indicate that the RLB assay is capable of reliably detecting yeasts and Aspergillus spp. in clinical specimens and that the incorporation of both ITS1- and ITS2-targeted probes is required for optimal sensitivity. The test has potential utility in the early diagnosis of invasive fungal infection, since "fungal" DNA was detected in all 27 specimens. Prior to incorporation of probes to detect other fungal species, ITS sequencing may be performed to achieve species identification.

Published ahead of print on 18 July 2007.

Xianyu Zeng and Fanrong Kong made similar contributions to the work and are listed as joint first authors.

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