Week 5 - Fungi Flashcards
1
Q
What is fungi nutrition?
A
- Fungi are heterotrophs that feed by absorption
a) Can be decomposers, parasites, or mutualists - They absorb nutrients via two main mechanisms:
a) Secrete hydrolytic enzymes which breaks down nutrients and macromolecules in their surroundings for absorption
b) Use enzymes to penetrate the walls of cells, enabling the fungus to absorb nutrients directly from the cell
2
Q
What is the fungi body structure?
A
- Most common body structures are multicellular filaments and single cells (yeasts)
- The cell walls of all fungi is composed of Chitin (a polysaccharide)
a) Cell wall is important in preventing cells bursting as nutrients are absorbed, which means diffusion and osmosis are taking place - In multi-cellular fungi, the hyphae form an interwoven mass called mycelium that infiltrates the fungi’s food source
a) Conidia - the hyphae that extend above surface and produce asexual spores; often pigmented and resistant to drying
b) Hyphae form compact tufts called mycelia which have a large surface area to volume - well adapted to absorb nutrients
c) If fungi is parasitic - hyphae can trap and kill prey such as helminths or living plant cells - DIAGRAM
- Some fungi produce macroscopic reproductive structures called fruiting bodies
- Fungal biology:
a) Eukaryotes
b) Non-motile
c) Aerobic
d) Cell wall contains glucan and chitin
e) Cell membrane contains ergosterol
3
Q
How do fungi reproduce?
A
- Asexually via three forms; growth and spread of hyphal filaments, asexual production of spores, simple cell division (budding yeasts)
- Sexually via sexual spores originating from fusion of two haploid cells to form a diploid cell
- Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually
4
Q
What are the types of fungal phylum?
A
- Chytrids:
a) Habitat: lakes and soil
b) Decomposers and parasites
c) Can be single cells and multicellular
d) Distinguishing feature: flagellated spores - Zygomycetes:
a) Fast-growing moulds responsible for causing food to rot
b) Fungi can act as decomposers, parasites, or as commensal symbionts
c) Distinguishing feature: during reproduction, they produce a sturdy structure called a zygosporangia which is resistant to freezing and drying (are metabolically inactive)
d) Reproduce asexually - Glomeromycetes:
a) Mutualistic partnership to more than 80% of all plants
b) Distinguishing feature: Form arbuscular mycorrhizae with plant roots - they supply minerals and other nutrients to the plant - Ascomycetes:
a) Habitat: marine, freshwater, and terrestrial habitats
b) Can be unicellular yeast, but many are elaborate cup fungi and morels
c) Have complex reproductive cycles with both sexual and asexual components
d) Distinguishing feature: they produce spores in a saclike asci - Basidiomycetes:
a) Important decomposers of wood and other plant material
b) Reproduce sexually
c) Distinguishing feature: they have a long lived heterokaryotic state in which each cell has two nuclei (one from each parent)
5
Q
How do you use CSF to distinguish pathogen involved in CNS infection?
A
- Colour:
a) Clear = viral
b) Cloud = bacterial or fungal - WBC:
a) Neutrophils elevated = bacterial
b) Lymphocytes elevated = fungal
6
Q
What is the pathogenesis of fungus?
A
- Toxins:
a) Produced but not relevant to human infections - Disease occurs from a bulk of organisms (fungi or fungal by-products) that cannot be taken care of by immune system due to number
7
Q
What are the types of fungal infections?
A
- Superficial (skin or mucosa)
- Subcutaneous
- Systemic:
a) True pathogens - infect healthy hosts
b) Opportunists - disease almost exclusively in immunocompromised individuals
8
Q
What are dermatophytes?
A
Superficial fungal infections
- Moulds producing keratinase
a) Saprophytes on skin/nails that eat at dead skin and cause inflammation - Types of diseases:
a) Tinea corporis
b) Tinea cruris
c) Tinea capitis
d) Tinea pedis
e) Tinea unguum
9
Q
What is Malassezia furfur?
A
Superficial fungal infection
- Lipophilic yeast
- Disease: Tinea versicolor (itch, pigment changes)
a) Occasionally, fungemia with lipid infusions
10
Q
What is the pathogenesis of subcutaneous fungal infections?
A
- Introduced through skin (puncture wound)
- Grow in subcutaneous tissues and is spread via lymphatics
a) May reach distant organs, especially bone
11
Q
What is Sporotrichosis?
A
Subcutaneous fungal infections
- Organism: Sporothrix schenkii
a) Dimorphic soil organism - Pathogenesis:
a) Splinters or thorns inoculate organism into subcutaneous tissues - Pathophysiology:
a) Yeast travels along lympthatics
b) Elicit mixed pyogenic/granulomatous reaction - Clinical:
a) Individuals who spend a good deal of time outdoors more susceptible
b) Ulcerating nodules along hard cord
c) If left untreated you can get bone and joint destruction, and if further untreated can lead to dissemination (rare)
12
Q
What are the fungal true pathogens?
A
Systemic fungal infections - e.g. Histoplasmosis, Coccidioidomycosis, and Blastomycosis
- Dimorphic
- Acquired through respiratory system
- Infect normal hosts and disease is reminiscent of TB
13
Q
What is Histoplasmosis?
A
Systemic fungal infection
- Organism: Histoplasma capsulatum
a) Dimorphic soil organism - Habitat: soils with high nitrogen content
a) Guano of bats, birds, and poultry - Pathogenesis:
a) Inhalation of spores - Pathophysiology:
a) Spores in lungs germinate to yeast
b) Yeast is taken up by phagocytic cells but overwhelms them and multiply extensively within phagocyte and will migrate to other organs
c) Yeast ellicits cellular immunity similar to TB (Hematogenous dissemination - Diagnosis:
a) Skin test reactivity test to histoplamin - Clinical:
a) Mimics TB
b) May disseminate early (infancy. immunodeficiency)
c) May cause acute nodular lung disease
d) May reactivate years later
14
Q
What is Coccioidomycosis?
A
Systemic fungal infection (true pathogen)
- Organism: Cocicoides immitis
a) Dimorphic soil organism
b) Spherules and endospores of spores - Pathogenesis:
a) Inhalation of spores - Pathophysiology:
a) Spores transform to spherules in lung
b) Elicit cellular immunity as per TB
c) Causes hematogenous dissemination - Diagnosis:
a) Skin test reactivity to coccoidin - Clinical:
a) Acute self-limited flu-like seroconversion
b) Dissemination (more prevalent in pregnancy, dark skin, immunocompromised); if untreated infection may spread to skin, bones, and CNS
15
Q
What is Blastomycosis?
A
True pathogen Systemic fungal infection
- Organism: Blastomyces dermatitidis
a) Dimorphic soil organism - Pathogenesis:
a) Inhalation of spores - Pathophysiology:
a) Spores transform into yeast in lung - Diagnosis:
a) No antigen test for Blastomycosis
b) Rule out Coccioidomycosis and Histoplasmosis first - Clinical:
a) Acute or chronic lung disease (nodular)
b) Disseminated disease that can spread to skin, bone, and urinary tract
