Introduction
Table of Contents
The genus Candida comprises a diverse group of opportunistic yeasts frequently isolated from human clinical specimens. Among them, Candida albicans remains the most common cause of infections; however, non-albicans Candida species, such as C. tropicalis, C. glabrata, and C. krusei, are increasingly recognized as important pathogens in immunocompromised patients, including those with malignancies. Differentiation between these species is essential, as their antifungal susceptibility patterns vary significantly, directly impacting patient management.
Microscopic examination provides a rapid, cost-effective, and reliable approach for distinguishing Candida species. Features such as the presence of chlamydospores, pseudohyphae, true hyphae, and blastoconidia arrangements form the cornerstone of comparative microscopy. C. albicans is uniquely identified by its ability to form chlamydospores, whereas non-albicans species exhibit characteristic morphological patterns such as elongated blastoconidia, cross-matchstick arrangements, or absence of pseudohyphae.
Comparative microscopy, especially on Corn Meal Agar with Tween 80, remains a vital diagnostic tool in clinical mycology laboratories. It provides valuable preliminary identification, guiding antifungal therapy while awaiting confirmatory methods such as MALDI-TOF MS or molecular sequencing.
Table
| Feature | Candida albicans | Candida tropicalis | Candida krusei | Candida glabrata |
|---|---|---|---|---|
| Chlamydospores | Present (large, thick-walled, round; terminal or intercalary) | Absent | Absent | Absent |
| Blastoconidia | Abundant, single or small clusters | Abundant, along pseudohyphae | Elongated blastoconidia, “tree-like” arrangement | Only blastoconidia (small, single, budding yeast cells) |
| Pseudohyphae | Well-developed, with constrictions at septa | Long, branched, with abundant blastoconidia | Elongated, branched with cross-matchstick appearance | Absent or very rare |
| True Hyphae | Present | Sometimes present | Rare | Absent |
| Corn Meal Agar (CMA) + Tween 80 | Produces chlamydospores (diagnostic) | Long pseudohyphae with blastoconidia | Elongated, branched with a cross-matchstick appearance | Only blastoconidia, no pseudohyphae |
| Microscopic Hallmark | Chlamydospores (diagnostic) | Long pseudohyphae + blastoconidia | Elongated blastoconidia (“matchstick”) | Elongated blastoconidia and pseudohyphae in a cross-matchstick pattern |
Keynotes
- Chlamydospores are a unique feature of C. albicans and are the most reliable diagnostic feature in routine microscopy.
- C. tropicalis shows abundant blastoconidia along pseudohyphae, but never chlamydospores.
- C. krusei produces elongated blastoconidia in a cross-matchstick arrangement.
- C. glabrata is unusual: only blastoconidia, no pseudohyphae or hyphae.
Further Readings
- Larone, D. H. (2018). Medically Important Fungi: A Guide to Identification. 6th Edition. ASM Press.
- Ellis, D., Davis, S., Alexiou, H., Handke, R., & Bartley, R. (2007). Descriptions of Medical Fungi. 2nd Edition. Mycology Unit, Women’s and Children’s Hospital, Adelaide.
- Kwon-Chung, K. J., & Bennett, J. E. (1992). Medical Mycology. Lea & Febiger.
- Koneman, E. W., Allen, S. D., Janda, W. M., Schreckenberger, P. C., & Winn, W. C. (1997). Color Atlas and Textbook of Diagnostic Microbiology. 5th Edition. Lippincott.
- Odds, F. C. (1988). Candida and Candidosis. 2nd Edition. Baillière Tindall.
- Clinical and Laboratory Standards Institute (CLSI). Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts; Approved Standard. CLSI Document M27.
- Pfaller, M. A., & Diekema, D. J. (2007). Epidemiology of invasive candidiasis: a persistent public health problem. Clinical Microbiology Reviews, 20(1), 133–163.