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Fungi

Eukaryotes
Chemoheterotrophs: organic compounds
Sterols present in membrane
No peptidoglycan in cell wall
Saprophytes
100,000 species (100 are pathogenic)
Mycology: Study of fungi
Molds
Yeasts

Molds

Thallus (body)
Hyphae (filaments)
- Septate (septa or crosswalls)
- Coenocytic (nonseptate) (no septa)

Mycelium (filamentous mass of hyphae)
- vegetative (nutrients)
- aerial (reproduction)

Yeasts

Nonfilamentous
Unicellular
Spherical or oval
Reproduce by budding

Dimorphism

Fungi exhibit two forms of growth
-- 37C: grow as yeast
-- 25C: grow as mold

Life Cycle of Fungi: Spores from Aerial Mycelia

Asexual Spores
- One organism
- genetically identical to parent
- Sporangiospore (in a sac) (sporangium-sac)
- Conidia: not enclosed in sac

Sexual spores
- Fusion of nuclei from 2 opposite mating strains

Nutritional Adaptations of Fungi

Grow in pH of 5.0
Molds: aerobic
Yeasts: facultative anaerobes
Grow in high sugar or salt, low moisture
Require less nitrogen
Metabolize complex carbohydrate

Fungal Diseases

Mycosis: fungal infection
Usually chronic (grow slowly) infection
Five groups based on degree of tissue involvement and mode of entry into body
systemic, subcutaneous, cutaneous, superficial, and opportunistic

Systemic Mycoses

Deep within the body
Affect number of tissues and organs
Caused by saprophytic fungi that live in soil
Route of transmission: inhalation of spores
Histoplasmosis (Histoplasma capsulatum)
Coccidioidomycosis (Coccidioides immitis)

Subcutaneous mycoses

Beneath the skin
Caused by saprophytic fungi that live in soil and on vegetation
Route of transmission: Direct implantation of spores in puncture wound
Sporothrix schenckii : gardeners

Cutaneous Mycoses (Dermatomycoses)

Caused by dermatophytes (fungi that infect only skin, nails and hair)
Secrete keratinase
Route of transmission: direct contact
- human to human
- contact with infected hairs and epidermal cell
Trichophyton, Epidermophyton, Microsporum

Opportunistic mycoses

Generally harmless in normal habitat
Become pathogenic in host who is immunocompromised
Mucormycosis: Rhizopus and Mucor
Aspergillosis: Aspergillus
- lung infections
Candidiasis: Candida albicans
- yeast infection, oral thrush

mycosis

fungal infection

Coenocytic

no septa

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