Introduction to mycology

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Fungi-Eucaryotes

Eucaryotic cells with characteristic organelles No chloroplasts Thick cell wall, mostly carbohydrate

Cellulose or chitin most common components Metabolically very similar, distinguished by

morphology 3 main types

Yeasts Filamentous fungi Dimorphic fungi

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Fungi

•Mycelial fungi •Yeasts •Dimorphic fungi

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Yeasts Unicellular fungi Grow by division

Budding Binary fission

Some times daughter cells may not detach themselves the result is a pseudohyphae

Yeast cell

Bud Pseudohyphae

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Filamentous fungi (molds) Multicellular, multinucleate Basic unit is the hyphae, a long thin filament Hyphae branch and cross link to form a mat (mycelium) Growth occurs at hyphal tip Hyphae may be divided by cross-walls (septa) into

uninuclear units Non septate hyphae: coenocytic Septa contain pore. All cytoplasm is connected.

Non-septate Septate

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Dimorphic fungi

Fungi able to switch between growth as a mycelium and a yeast

Depends on environmental conditions Usually one form is pathogenic and the other

is saprophytic Most cases yeast form is pathogenic, eg,

Histoplasma capsulatum In some cases hyphal form is pathogenic, eg,

Candida albicans

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Dimorphic fungi: Candida albicans

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Fungal spores: Vegetative spores

Arthrospores, eg, Coccidiodes immitis Chlamydospores, eg, Candida albicans Blastospores, eg, Candida albicans

Arthrospores Chlamydospores

Blastospores and pseudomycelium

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Fungal spores: Asexual spores

Some hyphae grow up from the mycelium and differentiate to produce spores

The most important of these are conidiospores The hyphae develops to produce a specialised

spore producing body called the conidiophore Some fungi produce large conidia containing

multinucleate spores (macroconidia) and small conidia which produce unicellular spores

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Conidiospores

Foot cell

Conidiophore

Sporing head

Aspergillus sp.

Section

Vesicle

Sterigma

Microsporum canis

Macroconidium

Microconidium

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Pathogenic mechanisms - Fungi Invasiveness: multiply in skin and keratin producing

common superficial infection (Ringworm, athletes foot)

Fungi gaining access to tissue cause subcutaneous infections

In the blood they cause life threatening systemic infections in the immunocompromised

Toxin production: ingestion of mouldy food in which fungal metabolites have been produced causes poisoning

Allergic reactions: inhalation of fungal hyphae or spores causes hypersensitivity reactions

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Cultivation of fungi

Fungi are chemoheterotrophs Growth requirements similar to bacteria some

require complex substances such as keratin Optimum growth temperature for many fungi

much lower than for pathogenic bacteria Most fungi grow at lower pH than bacteria Media

Sabourauds agar Dextrose and peptone, pH5.6

Yeast grow as colonies Filamentous fungi grow as a mycelium

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Terminology

Ascospore: asexual spore produced in a sac-like structure called an ascus

Arthospores: asexual spore formed by the disarticulation of the mycelium

Blastospores are formed by budding from the ends or sides of the parent cell, e.g., the yeast, Candida

Chlamydospores: thick-walled, resistant spores formed by the direct differentiation of hyphae

Conidia: asexual spore formed from hyphae by budding or septal division

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Terminology

Conidiophore: a stalk-like branch from the mycelium in which conidia develop either singly or in numbers

Germ tubes: tube-like structures produced by germinating spores

Hyphae: the filaments that composed the body of a fungus

Macroconidia: large multinucleate spores Microconidia: single-celled spores Mycelium: a mat made up of interwining thread-like

hyphae Pseudohyphae: filaments composed of elongated

budding cells that have failed to detach