Fungi

Morphology

Cytology:

• “Sticks and stones” appearance: pseudohyphae/ hyphae and yeasts
• Pseudohyphae have parallel side walls and constriction points.
• Gram-positive budding yeasts 3-6 µm
• Pseudohyphae and true hyphae vary by species. Candida albicans often shows true hyphae and pseudohyphae; Candida glabrata usually shows small blastoconidia without pseudohyphae.
• Neutrophils with intracellular yeasts are common in microabscess-forming purulent exudate.
• PAS and GMS positive.

Histology:
Yeasts, pseudohyphae and hyphae infiltrating epithelium or tissue with neutrophil-rich microabscesses. In angioinvasion, vascular thrombosis, and tissue necrosis.

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Material-specific Notes: (1)

• BAL/sputum: Candida usually indicates colonization. Pulmonary Candida infection cannot be confirmed cytologically; tissue invasion in biopsy is required. Purulent background, intraneutrophilic yeasts, and absence of other plausible pathogens may support suspicion but remain nonspecific.
• Sterile aspirates/abscess material: Candida in tissue, vessel walls, abscess wall, or intracellular location supports infection.
• Urine: Extracellular yeasts without inflammatory exudate usually suggest colonization. Intraneutrophilic yeasts with pyuria may support suspicion of infection, but are not diagnostic. (2)
• Skin/mucosa: Superficial Candida without microabscesses favors colonization. Penetrating pseudohyphae/hyphae with neutrophil-rich inflammation support infection.

Clinical correlation is essential, especially in immunocompromised patients.

Clinical notes

• Common clinical manifestations include oropharyngeal thrush, oesophagitis, vulvovaginal candidiasis, catheter-related candidemia, intra-abdominal candidiasis after perforation or surgery, and candiduria, which often represents colonization.
• Risk factors include broad-spectrum antibiotic exposure, diabetes, neutropenia, ICU stay, central venous catheters, and total parenteral nutrition.
• Candida glabrata has the potential to induce clinically significant vulvovaginitis and frequently demonstrates resistance to a broad spectrum of non‑prescription antifungal agents commonly employed in the management of candidiasis

Ancillary Testing

Chromogenic medium; MALDI-TOF; targeted PCR where available; blood cultures for candidemia; serum beta-D-glucan as adjunct; antifungal susceptibility testing for echinocandins and azoles, especially for C. glabrata and C. auris.

Additional Information

Frequent colonizer of sputum, oropharynx, vagina, skin, and urine.

The most common involved humanpathogenic species of Candida spp.:
-C. albicans
-C. glabrata
-C. parapsilosis-Komplex
-C. tropicalis
-C. krusei
-C. dubliniensis
-C. auris
-C. lusitaniae
-C. guilliermondii
-C. kefyr