Paper II — 2025 August (Supplementary) (2010 Scheme) — Q3
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Paper II
2025 August (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Laboratory diagnosis of candidiasis
Q35 marksShort Essays
Answer
Laboratory diagnosis of candidiasis (Candida species, most commonly C. albicans):
Direct microscopy — KOH mount or Gram stain of clinical specimen showing budding yeast cells, with or without pseudohyphae.
Culture — on Sabouraud dextrose agar (SDA), giving cream-coloured, smooth, pasty colonies within 24–48 hours; blood culture for suspected invasive/systemic candidaemia.
Germ tube test — the key rapid presumptive identification test for C. albicans: incubation in serum at 37°C for 2–3 hours produces a characteristic germ tube (filamentous outgrowth without constriction at its base); positive in C. albicans (and C. dubliniensis), negative in most other Candida species.
Chlamydospore formation — on cornmeal-Tween 80 agar, C. albicans produces characteristic thick-walled terminal chlamydospores.
CHROMagar Candida — a differential chromogenic medium giving characteristic colony colours for different Candida species, useful for rapid presumptive speciation, especially in mixed infections.
Biochemical/carbohydrate assimilation tests and automated identification systems for definitive species-level confirmation, particularly important given rising incidence of intrinsically more resistant non-albicans species (C. glabrata, C. krusei, C. auris).
Antifungal susceptibility testing — important for invasive candidiasis, given variable and rising resistance patterns.
Histopathology — biopsy (PAS or GMS stain) demonstrating tissue invasion, confirming invasive disease versus mere colonization.
Molecular methods (PCR) — increasingly used for rapid species identification directly from blood/sterile-site specimens.
