Introduction to Mycology

Question 1

General characteristics of fungi

Answer 1

Rigid cell wall (polysaccharides, mainly β-glucan and chitin)
Ergosterol in the cell membrane
Reproduction by spores
Lack of susceptibility to antibacterial antibiotics

Question 2

what is fungi important in

Answer 2

Ecology
Commercial
Pharmaceutical
Pathogens

Question 3

Fungi- what are the thee types

Answer 3

Eukaryotic
Unicellular (yeasts) or multicellular
3 types:
yeasts (e.g. Candida albicans)
multicellular filamentous moulds (e.g. Aspergillus, Trichophyton spp.)
macroscopic filamentous fungi (form large fruiting bodies, i.e. mushrooms)

Question 4

fungal cell structure

Answer 4

vacuole
nucleus-DNA and RNA
membrane
cell wall
er
g
MITOHONDRIA
tubulin

Question 5

Fungal cell wall

Answer 5

mannan
beta-glucan
chitin
membrane contains ergosterol double membrane

Question 6

yeast

Answer 6

single cells, reproduce by budding or fission
can form spores

N.B. some fungi are dimorphic - can switch between yeast and hyphal forms

Question 7

mould

Answer 7

grow as masses of overlapping and interlinking hyphal filaments (mycelium)
reproduce by formation of spores

Question 8

Mycelium

Answer 8

Hypha (singular: hyphae) collectively form a mycelium
Can be septate or non-septate
In septate hypha the cytoplasm is connected by large pores in the septa

Hypha grow at the tips

Question 9

Dimorphic fungi

Answer 9

Can grow as yeasts OR form hyphae
Usually form hyphae at environmental temperatures, and grow as yeast cells in the body - conversion is triggered by temperature (e.g. Histoplasma spp.)
Candida spp. do the reverse - form hypha within the body

Question 10

Categories of mycoses

Answer 10

Superficial and cutaneous mycoses
Subcutaneous mycoses
Systemic/deep mycoses

Question 11

Superficial and cutaneous mycoses

Answer 11

• fungus grows on body surface
  e.g. athlete’s foot, vaginal candidiasis, oral thrush, ringworm, onythomycosis

Question 12

Subcutaneous mycoses

Answer 12

deeper layers of skin involved without dissemination to distant sites
usually involves saprophytes, infection due to traumatic inoculation
Sporotrichosis
(Sporothrix schenkii

Question 13

Systemic/deep mycoses

Answer 13

infection mainly through lungs, but may become widely disseminated and involve any organ system
by primary or opportunistic pathogens; e.g. histoplasmosis-Histoplasma capsulatum, systemic candidiasis, Pneumocystosis - Pneumocystis jiroveci

Question 14

Dermatophytes

Answer 14

Infection often spreads out as circle, with healing skin in middle (hence “ringworm”)

Cause Tinea infections most common infection
E.g. tinea corporis; tinea capitis; tinea pedis, tinea unguium

One of very few fungi to have evolved dependency on human/animal infection

Infection direct (human/animal) contact or indirect (e.g. swimming pool, shower, towels etc.)

Question 15

Treatment of fungal infections

Answer 15

Bacterial antibiotics are not effective against fungal infections
Many antifungals act on the membrane lipid ergosterol
inhibition of synthesis (leading to accumulation of toxic sterol intermediates)
OR direct binding (results in leaky cells)
Others act on DNA/RNA synthesis or microtubules
many antifungals act on the membrane lipid ergosterol

Question 16

candida albicans

Answer 16

type: dimorphic
category: superficial-systermic
disease; oral or vaginal thrush, nail/skin infections, sepsis

Question 17

Trichophyton spp

Answer 17

type mould
category: cutaneous
disease: dermatophytosis (tinea infections) ; athletes foot, ringworm, onthychomycosis