Introduction to Fungi

Define fungi and mycology

Fungi : Eukaryotic microbes where some can cause superficial, cutaneous, subcutaneous, or systemic disease

Mycology: Study of fungi

Basic features of Fungi?

• Saprophytic, parasitic, or commensal organism

• All fungi are heterotrophs

• Majority are obligate aerobes (limited anearobic capabilities)

• Majority can grow in ordinary culture media.

Basic structure of Fungi?

Structure

• Eukaryotic cell structure = Genetic material differentiated into chromosomes and cell contains ribosomes (80S rRNA) and mitochondria

1. Cell walls : Chitin, polysaccharide, polypeptide, B glucan

2. Cell (plasma) memb: contains sterols especially ergosterol = prevent antibiotics being effective against fungi

3. Microtubules composed of tubulin

Pathogenicity: Superficial vs Subcutaneous vs systemic mycosis vs Opportunistic vs Mycotoxicosis (examples)

• Superficial mycosis = Affecting skin, hair or nails. Eg: pityriasis versicolor

• Subcutaneous mycosis = aka Implantation mycosis. Eg: mycetoma

• Systemic mycosis = aka Deep mycosis. Eg: histoplasmosis

• Opportunistic mycosis. Eg: in HIV patient or other disease causing immunosuppression

• Mycotoxicosis = Mycotoxins in mouldy food stored under damp humid condition. Eg Alfa toxins produced by Aspergillus flavus when growing in peanuts and grains

Define Hypha and Mycelium and Dimorphism

Hypha (pleural hyphae) : Microscopic branching filaments can be divided into cells by septum (septate) or non (non-septate)

Mycelium : Visible mass of interwoven hyphae

Dimorphism : Fungus which occurs in 2 forms

Define Mould and Yeast

Mould: Fungus which produces hyphae

Yeast: Fungi which reproduce by budding

Fungal spores importance & 5 principal types

Importance:

• Most fungi reproduce by forming spore

• Spore size,shape ,colour and manner of production are important in identification

Principal types of spores:

1. Chlamydospore

2. Arhtrospore

3. Blastospore

4. Conidium

5. Sporangiospore

Define Chlamydospore

Chlamydospore: resting stage formed when cell swells up and develops thick wall

Define Arthrospore

Arthrospore: Spore formed by septation followed by fragmentation of a hypha

Define Blastospore

Blastospore: Single vegetative yeast cell produced by budding

Define Conidium

Conidium (pleural conidia) : Spore produced externally on (specialised hypha) conidiophore → becomes detached when mature → important in identification

Define Sporangiospore

Sporangiospore: spore produced within swollen spherical cell (sporangium) at end of sporangiophore (specialised hypha)

Taxonomy of fungi Candida albicans (Kingdom, Phylum, subphylum, class, order,family, genus, species

Kingdom: Fungi

Phylum: mycota

Subphylum: mycotina

Class: mycetes

Order: ales

Family: acea

Genus: Candida

Species: Albicans

Classification of fungi

1. Classify fungi on what basis

2. Ascomycota, vs Basidomycota, vs Zygomycota vs Fungi imperfect (class, sexual reproduction, asexual reproduction)

• Fungi classified on basis of ability to reproduce sexually, asexually or combo

• All fungal genera of medical importance for human is 1 of 4…

Ascomycota

Class: Ascomycetes

Sexual: Ascospores

Asexual: Conidia

Basidomycota

Class: Basidomycetes

Sexual: Basidiospores

Asexual: Conidia

Zygomycota

Class: Zygomycetes

Sexual: Zygospores

Asexual: Conidia

Fungi Imperfecti

Class: X

Sexual: X

Asexual: Sporangiospores