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Published on: December 28, 2017
Molecular identification of Candida orthopsilosis isolated from blood culture
P V C Yong1, P P Chong, L Y Lau
1Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, University Putra Malaysia, 43400 Serdang, Malaysia.
Abstract:
The incidence of candidemia and invasive candidiasis have increased markedly due to the increasing number of immunocompromised patients. There are five major medically important species of Candida with their frequency of isolation in the diminishing order namely Candida albicans, Candida parapsilosis, Candida tropicalis, Candida glabrata and Candida krusei. In addition, there are numerous other species of Candida which differ in their genetic makeup, virulence properties, drug susceptibilities and sugar assimilation capabilities. In this report, an unusual Candida species was isolated from the blood of two leukaemic patients. Conventional culture and biochemical tests identified the Candida species as C. parapsilosis. Using fungal-specific oligonucleotide primers ITS1 and ITS4, we managed to amplify the ribosomal RNA gene and its internal transcribed spacer region from the genomic DNA of these isolates. The PCR products were then purified and subjected to automated DNA sequencing using BLAST and CLUSTAL sequence analysis identified these isolates to be Candida orthopsilosis. Candida orthopsilosis is a new species recently identified in 2005, being morphologically indistinguishable from C. parapsilosis and was previously classified as a subspecies of C. parapsilosis. This report highlights the importance of complementing traditional culture and biochemical-based identification methods with DNA-based molecular assays such as PCR as the latter is more superior in terms of its discriminatory power and speed.
Insights
Molecular methods accurately identified Candida orthopsilosis, a species previously mistaken for Candida parapsilosis, in leukaemic patients. This highlights the importance of advanced diagnostics for fungal infections.
Area of Science:
- Medical Mycology
- Molecular Biology
- Infectious Diseases
Background:
- Candidemia and invasive candidiasis are rising, particularly in immunocompromised individuals.
- Five main Candida species (C. albicans, C. parapsilosis, C. tropicalis, C. glabrata, C. krusei) are commonly isolated.
- Numerous other Candida species exist with varying genetic, virulence, and drug susceptibility profiles.
Purpose of the Study:
- To report the isolation of an unusual Candida species from leukaemic patients.
- To compare conventional identification methods with molecular techniques for Candida species.
- To emphasize the significance of accurate fungal identification in clinical settings.
Main Methods:
- Isolation of Candida species from blood samples of leukaemic patients.
- Conventional culture and biochemical testing for initial identification.
- Polymerase Chain Reaction (PCR) using ITS1 and ITS4 primers to amplify ribosomal RNA gene.
- Automated DNA sequencing and BLAST/CLUSTAL analysis for precise species identification.
Main Results:
- Conventional methods initially identified the isolates as Candida parapsilosis.
- Molecular analysis revealed the isolates to be Candida orthopsilosis, a recently identified species.
- Candida orthopsilosis is morphologically indistinguishable from Candida parapsilosis.
Conclusions:
- DNA-based molecular assays like PCR offer superior discriminatory power and speed compared to traditional methods.
- Accurate identification of Candida species is crucial for effective management of invasive fungal infections.
- This case underscores the need to integrate molecular diagnostics into routine laboratory practice for identifying emerging fungal pathogens.
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