21 - Intro to Mycology and Fungal Diseases Flashcards
Three domains of life
Bacteria, Archaea, Eukarya
What is the universal phylogenetic tree based on
16s rRNA sequences
Fungi
Describes a diverse group of eukaryotic organisms that are spore bearing, have absorptive nutrition, do not photosynthesise, and reproduce both sexually and asexually
Characteristics of fungi
- Eukaryotic (nucleus, mitochondria, etc)
- Have cell walls
- Heterotrophic, osmotrophic, and saprophytic nutrition
- Basic unit is hyphae
- Have simple to complex life cycles involving asexual and sexual reproduction, and spore production
Heterotrophic
Use reduced, preformed organic molecules as carbon source
Osmotrophic
Soluble nutrients are absorbed through the cytoplasmic membrane
Saprophytic
Derive nutrition from degradation of dead organic matter
Hypha (pl. hyphae)
- Tubular branching filament
- A mass of branching hyphae = mycelium
- Mycelium is a type of thallus (body or vegetative structure of fungus)
Aseptate (coenocytic) hyphae
Multinucleate protoplasm streams through the hyphae
Septate hyphae
have septa (cross walls) with pores to allow streaming of protoplasm
Yeasts
Fungi but typically are unicellular, bud, and do not have a mycelial stage
Mould
Term used for fungi producing filamentous growth
Dimorphic fungi
- Mycelial form outside host
- Yeast form in host
Thermally dimorphic fungi
Cell shape changes, composition of the cell wall differs, presence of antigens differs, and virulence increases/decreases
Asexual reproduction
- Elongation of hyphae, or budding of yeast cells to form a smaller daughter cell
- Often accompanied by formation of asexual spores
Sexual reproduction
- Fusion of nuclei, meiosis, mitosis
- Produces sexual spores
Sexual fungi spores
- Enable fungi to survive
drying, heating, starvation, some chemicals - Both sexual and asexual
spores can germinate to form new hyphae
Types of asexual spores
- Sporangiospores
- Conidiospores:
- Arthrospores (arthroconidia)
Sporangiospores
produced in a membrane enclosed structure termed a ‘sporangium’
Conidiospores
Pores born on tips or sides of ‘conidiophores’ – not enclosed in a membrane
Arthrospores
formed when hyphae fragment
Basidiospores
Sexual spores produced on the end of a club shaped structure or “basidium”
Mycoses
Fungal diseases
Systemic mycoses
- Most acquired by an air-borne route
- Spores are inhaled from the soil where the free-living fungi are found
- The fungal pathogens are often thermally dimorphic
Types of systemic mycoses
- Coccidioidomycosis
- Cryptococcosis
- Histoplasmosis
Coccidioidomycosis
- aka Valley fever
- Coccidioides immitis
- Thermally dimorphic fungus
Coccidioidomycosis in soul and on culture media
Grows as a filamentous mould that forms arthroconidia at the tips of hyphae
Coccidioidomycosis in humans
Grows as a thick-walled spherule filled with spores
Coccidioidomycosis life cycle
- Arthroconidium germinates into tubular hypa
- Hypha begins to segment into arthroconidia
- Airborne arthroconidium is inhaled
- Inhaled arthroconidium enlarges and begins to develop into a spherule
- Endospores develop within spherule
- Spherule releases endospores which spread in tissue (each developing into new spherule)
Coccidioidomycosis clinical features
- Flu like symptoms, most recover
- Pneumonia
- Chronic, progressive lung disease, may be fatal
Cryptococcosis
- Geographically ubiquitous organism
- In host, and isolated in lab, as large spherical yeast cells
- Can be mycelial in environment or smaller yeast cells
- Infection by inhalation of basidiospores
- C. gatti causes disease in immunocompromised
- C. neoformans infects people with HIV
Clinical features of Cryptococcosis
- Meningoencephalitis
- Pneumonia
- Skin lesions
Cryptococcosis diagnosis
- Direct Microscopy (India Ink stain)
- Yeast cells have capsules which exclude ink particles, so cell appears surrounded by clear area
- Culture is used to tell if a cryptococcal infection is C. neoformans or gattii
Histoplasmosis
- Soil & bat/bird droppings link
- Histoplasma capsulatum thermally dimorphic
- Survival and multiplication in phagocytes
- Microconidia become air borne and are inhaled
- Disease of lungs
- May disseminate to many organs via infected macrophages
Categories of mycoses
- Superficial
- Cutaneous
- Subcutaneous
- Systemic
- Opportunistic
