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fungi

Tuesday 6 September 2005

Definition: Fungi are eukaryotes that possess thick chitin-containing cell walls and ergosterol-containing cell membranes.

Fungi can grow either as budding yeast cells or as slender filamentous hyphae. Hyphae may be septate (with cell walls separating individual cells) or aseptate, which is an important distinguishing characteristic in clinical material.

Some of the most important pathogenic fungi exhibit thermal dimorphism; that is, they grow as hyphal forms at room temperature but as yeast forms at body temperature.

Fungi may produce sexual spores or, more commonly, asexual spores referred to as conidia. The latter are produced on specialized structures or fruiting bodies arising along the hyphal filament.

Fungi may cause superficial or deep infections. Superficial infections involve the skin, hair, and nails. Fungal species that are confined to superficial layers of the human skin are known as dermatophytes.

These infections are commonly referred to by the term "tinea" followed by the area of the body affected (e.g., tinea pedis: "athlete’s foot," tinea capitis: "ringworm of the scalp"). Certain fungal species invade the subcutaneous tissue, causing abscesses or granulomas, (e.g., sporotrichosis and tropical mycoses).

Deep fungal infections can spread systemically and invade tissues, destroying vital organs in immunocompromised hosts, but usually heal or remain latent in otherwise normal hosts.

Some deep fungal species are limited to a particular geographic region (e.g., Coccidioides in the southwestern United States and Histoplasma in the Ohio River Valley).

Opportunistic fungi (e.g., Candida, Aspergillus, Mucor, and Cryptococcus), by contrast, are ubiquitous organisms that colonize normal human skin or gut without causing illness.

Only in immunosuppressed individuals do opportunistic fungi give rise to life-threatening infections characterized by tissue necrosis, hemorrhage, and vascular occlusion, with minimal to no inflammatory response. In addition, AIDS patients are victims of the opportunistic fungus Pneumocystis jiroveci (carinii).

Fungi are eukaryotes that grow predominantly by budding (yeasts) or by filamentous extensions called hyphae (molds). Fungi are etiological agents of fungal infections.

Types

- List of Fungi

Some fungi, such as Candida albicans, tend to grow predominantly as yeast but may also form hyphae.

Dimorphic fungi have both a yeast form (at human body temperature) and a mold form (at room temperature).

Links

- Mycology Online
- Infections fongiques (fungal infections) (in french) by Pierre Brochu, MD, Université de Montréal, QC
- Fungal genomes: Wiki and blog

See also

- fungal infections
- dimorphic fungi

References

- Claudia M, Bacci A, Silvia B, Gaziano R, Spreca A, Romani L. The interaction of fungi with dendritic cells: implications for Th immunity and vaccination. Curr Mol Med. 2002 Sep;2(6):507-24. PMID: 12243244

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