Introduction to Fungi

Question 1

Explain the structure of fungi.

Answer 1

Fungi are eukaryotic, they lack chlorophyll and form spores.

Question 2

State what is meant by the term ‘chemoorganotroph’?

Answer 2

An organism (such as fungi) that can obtain its energy from the oxidation of reduced organic compounds.

Question 3

Explain briefly the classification of fungi.

Answer 3

• Their classification is based on morphology
• The fungal kingdom is divided into 3 groups which are:
• Basidiomycetes
• Astromycetes
• Zygomycetes

Question 4

Give an example of a basidiomycete as well as a sexual and asexual spore.

Answer 4

Example: Mushroom
Sexual spore: Basidiospore
Asexual spore: Conidium

Question 5

Give an example of an ascomycete as well as a sexual and asexual spore.

Answer 5

Examples: Neurospora and Saccharomyces
Sexual spore: Ascospore
Asexual spore: Conidium

Question 6

Give an example of a zygomycete as well as a sexual and asexual spore.

Answer 6

Example: Bread moulds
Sexual spore: Zygospore
Asexual spore: Sporangiospore

Question 7

Describe the clinically important systemic and dermatophytic fungal infections.

Answer 7

Dermatophytosis:

• Moulds which degrade keratin as a nutrient source, causing infection of the hair, nails or skin.
• Caused by Epidermophyton Microsporum and Trichophytonspp
• Can be characterised as ‘ringworm’ infections

Pityriasis versicolor:

• Discolouration of skin
• Yeasts that also form hyphae in infected skin
• Caused by Malassezia spp

Question 8

Describe the properties of fungi.

Answer 8

• They are a significant cause of non-fatal diseases
• This includes athlete’s foot (tinea pedis), thrush and pityriasis versicolor
• They are increasingly responsible for fatal diseases
• More than 500 fungal species have been recorded as rare human pathogens.

Question 9

Describe the host factors that contribute to the pathogenicity of fungal infections

Answer 9

• Warm and moist areas are favourable microenvironment for fungi to grow on the skin and mucous membranes.
• Broad-spectrum antibacterial agents reduce competition for epithelial colonisation sites in the gut
• Immunosuppression of all types may create a window of opportunity for fungal invasion.

Question 10

Describe the diagnostic methods for detecting fungi.

Answer 10

• Direct detection - This can include histopathology and high resolution CT scans
• PCR for fungal DNA
• Culture of fungus from normally sterile site

Question 11

State the yeast that causes pityriasis versicolour

Answer 11

Malassezia spp

Question 12

Describe the mechanisms of action of anti-fungal drugs, their route of administration and issues associated with anti-fungal agents:
Triazoles and allyamines

Answer 12

These target sterols (steroid alcohols)

Question 13

Describe the mechanisms of action of anti-fungal drugs, their route of administration and issues associated with anti-fungal agents:
Echinocandins

Answer 13

These target the fungal cell wall

Question 14

Describe the mechanisms of action of anti-fungal drugs, their route of administration and issues associated with anti-fungal agents:
Polyenes

Answer 14

These target the fungal cell membrane

Question 15

Describe the mechanisms of action of anti-fungal drugs, their route of administration and issues associated with anti-fungal agents:
Flucytosine

Answer 15

These target DNA synthesis

Question 16

Give 3 examples of echinocandins

Answer 16

Caspofungin
Anidulafungin
Micafungin

Question 17

Give 2 examples of polyenes

Answer 17

Amphotericin B

Nystyatin