A 34-year-old woman with poorly controlled type 2 diabetes mellitus (HbA1c 9.2%) presents with a 2-week history of vulvovaginal itching, thick white vaginal discharge, and vulvar erythema. She denies fever or systemic symptoms. Wet mount microscopy shows pseudohyphae and budding yeast. Culture on Sabouraud dextrose agar at 37°C grows white, creamy colonies that form germ tubes in human serum at 37°C. Which Candida species is most likely responsible for this infection?

Explanation

## Identification of Candida albicans **Key Point:** Candida albicans is the most common cause of vulvovaginal candidiasis, particularly in immunocompetent individuals with predisposing factors such as diabetes, antibiotic use, or hormonal changes. ### Diagnostic Features of C. albicans | Feature | C. albicans | C. glabrata | C. auris | C. tropicalis | |---------|-----------|-----------|---------|---------------| | **Germ tube test** | Positive (37°C in serum) | Negative | Negative | Positive | | **Chlamydospore formation** | Yes (on cornmeal agar) | No | No | No | | **Colony morphology** | White, creamy, smooth | White, small, mucoid | White/grey, mucoid | White, creamy | | **Common site** | Vagina, oral cavity | Vagina (resistant strains) | Nosocomial, ICU | Tropical regions | | **Antifungal resistance** | Low (fluconazole-sensitive) | High (fluconazole-resistant) | High (multidrug-resistant) | Low-moderate | **High-Yield:** The **germ tube test** is the gold standard for rapid identification of C. albicans in clinical practice. A positive result (formation of hyphal projections from yeast cells incubated in human serum at 37°C for 2–3 hours) is 95% specific for C. albicans and C. dubliniensis. **Clinical Pearl:** Vulvovaginal candidiasis in a diabetic patient reflects impaired neutrophil function and elevated glucose in vaginal secretions, creating an ideal environment for Candida proliferation. Hyperglycemia (HbA1c >9%) is a well-established risk factor. **Mnemonic: GERM** — Germ tube test, Extracellular enzymes (protease, lipase), Resistance to fluconazole (low), Mucoid colony morphology. ### Why C. albicans is the Answer 1. **Germ tube positivity** — The vignette explicitly states germ tube formation in human serum at 37°C, which is pathognomonic for C. albicans (and C. dubliniensis, which is rare). 2. **Most common cause** — C. albicans accounts for ~90% of vulvovaginal candidiasis cases. 3. **Clinical context** — Poorly controlled diabetes is a classic risk factor; C. albicans thrives in hyperglycemic states. 4. **Colony morphology** — White, creamy colonies on Sabouraud agar are typical of C. albicans. [cite:Textbook of Microbiology Ananthanarayan & Paniker 10e Ch 59]