40. Pathogenic fungi. Candida spp. Morphology, biology. Pathogenesis and clinical forms. Immunity. Microbiological diagnosis. Therapy. Aspergillus, Cryptococcus, Actinomycetaceae. Morphology, biology, disease and microbiological diagnosis.

I. General Characteristics

• Eukaryotic organisms with cell walls composed of chitin and glucans.
• Classified by reproduction and morphology:
• Yeasts: unicellular; reproduce by budding (e.g., Candida).
• Molds: multicellular hyphae forming mycelium (e.g., Aspergillus).
• Dimorphic fungi: exist as molds at 25°C and yeasts at 37°C (e.g., Histoplasma).
• Stained with PAS, GMS (silver), and India ink (for Cryptococcus).
• Fungal infections = mycoses:
• Superficial, cutaneous, subcutaneous, systemic, and opportunistic types.

Candida spp.

III. Key Features

• Oval budding yeasts that form pseudohyphae and germ tubes (esp. C. albicans).
• Normal flora of skin, GI tract, vagina.
• Dimorphic (but yeast in tissue, pseudohyphae in culture).
• Most common species: Candida albicans, Candida glabrata, C. tropicalis.

IV. Clinical Manifestations

• Mucocutaneous candidiasis: oral thrush, vulvovaginitis, diaper rash.
• Esophagitis: common in AIDS patients.
• Invasive candidiasis: bloodstream infection (candidemia), endocarditis (especially in IV drug users, catheterized patients), hepatosplenic candidiasis in neutropenic patients.

V. Diagnosis & Treatment

• KOH prep, Gram stain, germ tube test (positive for C. albicans).
• Culture on Sabouraud agar.
• Treatment:
• Topical azoles (e.g., clotrimazole) for superficial infections.
• Fluconazole or echinocandins (e.g., caspofungin) for systemic infections.
• Amphotericin B for severe/disseminated disease.