21 - Intro to Mycology and Fungal Diseases

Question 1

Three domains of life

Answer 1

Bacteria, Archaea, Eukarya

Question 2

What is the universal phylogenetic tree based on

Answer 2

16s rRNA sequences

Question 3

Fungi

Answer 3

Describes a diverse group of eukaryotic organisms that are spore bearing, have absorptive nutrition, do not photosynthesise, and reproduce both sexually and asexually

Question 4

Characteristics of fungi

Answer 4

1. Eukaryotic (nucleus, mitochondria, etc)
2. Have cell walls
3. Heterotrophic, osmotrophic, and saprophytic nutrition
4. Basic unit is hyphae
5. Have simple to complex life cycles involving asexual and sexual reproduction, and spore production

Question 5

Heterotrophic

Answer 5

Use reduced, preformed organic molecules as carbon source

Question 6

Osmotrophic

Answer 6

Soluble nutrients are absorbed through the cytoplasmic membrane

Question 7

Saprophytic

Answer 7

Derive nutrition from degradation of dead organic matter

Question 8

Hypha (pl. hyphae)

Answer 8

• Tubular branching filament
• A mass of branching hyphae = mycelium
• Mycelium is a type of thallus (body or vegetative structure of fungus)

Question 9

Aseptate (coenocytic) hyphae

Answer 9

Multinucleate protoplasm streams through the hyphae

Question 10

Septate hyphae

Answer 10

have septa (cross walls) with pores to allow streaming of protoplasm

Question 11

Yeasts

Answer 11

Fungi but typically are unicellular, bud, and do not have a mycelial stage

Question 12

Mould

Answer 12

Term used for fungi producing filamentous growth

Question 13

Dimorphic fungi

Answer 13

• Mycelial form outside host
• Yeast form in host

Question 14

Thermally dimorphic fungi

Answer 14

Cell shape changes, composition of the cell wall differs, presence of antigens differs, and virulence increases/decreases

Question 15

Asexual reproduction

Answer 15

• Elongation of hyphae, or budding of yeast cells to form a smaller daughter cell
• Often accompanied by formation of asexual spores

Question 16

Sexual reproduction

Answer 16

• Fusion of nuclei, meiosis, mitosis
• Produces sexual spores

Question 17

Sexual fungi spores

Answer 17

• Enable fungi to survive
  drying, heating, starvation, some chemicals
• Both sexual and asexual
  spores can germinate to form new hyphae

Question 18

Types of asexual spores

Answer 18

• Sporangiospores
• Conidiospores:
• Arthrospores (arthroconidia)

Question 19

Sporangiospores

Answer 19

produced in a membrane enclosed structure termed a ‘sporangium’

Question 20

Conidiospores

Answer 20

Pores born on tips or sides of ‘conidiophores’ – not enclosed in a membrane

Question 21

Arthrospores

Answer 21

formed when hyphae fragment

Question 22

Basidiospores

Answer 22

Sexual spores produced on the end of a club shaped structure or “basidium”

Question 23

Mycoses

Answer 23

Fungal diseases

Question 24

Systemic mycoses

Answer 24

• 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

Question 25

Types of systemic mycoses

Answer 25

- Coccidioidomycosis - Cryptococcosis - Histoplasmosis

Question 26

Coccidioidomycosis

Answer 26

- aka Valley fever - Coccidioides immitis - Thermally dimorphic fungus

Question 27

Coccidioidomycosis in soul and on culture media

Answer 27

Grows as a filamentous mould that forms arthroconidia at the tips of hyphae

Question 28

Coccidioidomycosis in humans

Answer 28

Grows as a thick-walled spherule filled with spores

Question 29

Coccidioidomycosis life cycle

Answer 29

1. Arthroconidium germinates into tubular hypa 2. Hypha begins to segment into arthroconidia 3. Airborne arthroconidium is inhaled 4. Inhaled arthroconidium enlarges and begins to develop into a spherule 5. Endospores develop within spherule 6. Spherule releases endospores which spread in tissue (each developing into new spherule)

Question 30

Coccidioidomycosis clinical features

Answer 30

- Flu like symptoms, most recover - Pneumonia - Chronic, progressive lung disease, may be fatal

Question 31

Cryptococcosis

Answer 31

- 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

Question 32

Clinical features of Cryptococcosis

Answer 32

- Meningoencephalitis - Pneumonia - Skin lesions

Question 33

Cryptococcosis diagnosis

Answer 33

- 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

Question 34

Histoplasmosis

Answer 34

- 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

Question 35

Categories of mycoses

Answer 35

- Superficial - Cutaneous - Subcutaneous - Systemic - Opportunistic