85. Pathogenic fungi. Candida. Cryptococcus, Histoplasma, Aspergillus, etc

Covers the general features of pathogenic fungi, classing them as yeasts, moulds and dimorphic forms, and their staining methods. A summary table compares major genera such as Candida, Cryptococcus, Histoplasma and Aspergillus, along with Blastomyces, Coccidioides, Paracoccidioides, Pneumocystis and Mucor. Each organism is then taken in turn with its key features, clinical manifestations, diagnosis and treatment.

Inside: 9 sections · 9 labelled pictures · 1 table · 16 flashcards · 4 min

Topic 85 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 417 words (4 min of reading), with 16 flashcards.

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.