Summary auto-generated
This review examines molecular genetic techniques for identifying, typing, and classifying non-albicans Candida species, which are increasingly reported in infections, particularly among immunocompromised patients including those with HIV. While C. albicans remains the most common cause of candidiasis, other species are being isolated more frequently, raising questions about antifungal drug resistance. The paper discusses various molecular approaches including species-specific DNA probes for Southern hybridization, tRNA profile analysis, PCR with ribosomal and lanosterol-α-demethylase gene primers, and DNA fingerprinting techniques. For strain typing, methods include restriction fragment length polymorphism, pulsed-field gel electrophoresis, Southern hybridization with repetitive DNA probes, oligonucleotide fingerprinting, karyotype analysis, and random amplified polymorphic DNA (RAPD). The authors emphasize that these molecular techniques overcome limitations of traditional phenotypic identification methods and improve epidemiological investigations. The review highlights the discovery of C. dubliniensis as a novel species and discusses how molecular approaches can resolve taxonomic ambiguities within the Candida genus that have resulted from relying on morphological and physiological characteristics.
Key findings
- Species-specific DNA probes and PCR methods enable rapid molecular identification of non-albicans Candida species from clinical specimens within hours, compared to 24-48 hours for conventional culture methods
- Multiple molecular strain typing approaches (DNA fingerprinting, RAPD, oligonucleotide probes) effectively discriminate between isolates for epidemiological tracking and detecting multiple strains in clinical specimens
- tRNA profile analysis and PCR targeting ribosomal and lanosterol-α-demethylase genes provide reliable species identification for C. glabrata, C. krusei, C. tropicalis, C. parapsilosis, and C. guilliermondii
- Molecular techniques can resolve taxonomic ambiguities in Candida classification by confirming relationships between anamorphic Candida species and their teleomorphic counterparts, exemplified by C. dubliniensis discovery
- PCR and oligonucleotide fingerprinting offer advantages over traditional methods including non-species-specific probes, better reproducibility, and ability to detect minor polymorphisms among closely related isolates
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Abstract
The reported incidence of fungal infections associated with non-albicans species from the Candida genus is increasing. Most of these infections occur in immunocompromised patients, particularly those infected with HIV. The role of molecular genetic techniques alongside the existing techniques for the identification and typing of these organisms is discussed. Species-specific genomic DNA fragments cloned from C. tropicalis and C. krusei have been developed for identification and strain typing. Analysis of tRNA profiles has been shown to be effective for the identification of C. glabrata, C. guilliermondii, C. parapsilosis and C. tropicalis. A PCR method employing primers complimentary to large ribosomal subunit genes and the lanosterol-alpha-demethylase gene has been applied for several species, including C. glabrata, C. krusei and C. tropicalis. Strain typing by comparison of genomic DNA fingerprints has been demonstrated for C. tropicalis and C. krusei following hybridisation analysis with species-specific probes. Synthetic oligonucleotide probes--which do not have to be species-specific and which can detect minor polymorphisms--have also been used for strain typing of isolates of several non-albicans species. Random amplification of polymorphic DNA (RAPD) has also been used for analysis of C. glabrata, C. lusitaniae and C. tropicalis isolates. The potential for the application of these and other techniques to Candida spp. taxonomy--and the example of a recently discovered novel species, C. dubliniensis--is discussed.