Fungi

Question 1

What are the three ways in which fungi can be classified?

Answer 1

Unicellular (yeast)
Filamentous (mould)
Dimorphic (can switch between the above two forms)

Question 2

List some features of unicellular fungi

Answer 2

Yeasts are facultative anaerobes, asexual reproduction (budding), they can produce colonies on agar (commonly confused for bacteria but their colonies are larger), mainly invade host via the respiratory epithelium

Question 3

List some features of Filamentous fungi

Answer 3

Aerobes
Asexual reproduction (conidia - spores)
Produce mycelia on agar
Have hypha (long multicellular filaments)

Question 4

List the types of fungi in descending virulence

Answer 4

Dimorphic fungi (filamentous in environment and yeast form when infect us)
Dermatophytes (ringworm grows where kerratin is - hair and skin. Heal from the inside out)
Agents of subcutaneous myocytes ( low grade infections)
Opportunists
Toxic fungi (toxins diffuse through bread or tomato)

Question 5

What do dermatophytes cause

Answer 5

Tinea

Question 6

What type of sample would you collect for investigation of Dermatophytes?

Answer 6

Skin scraping

Question 7

What are the three genera of Dermatophytes?

Answer 7

Microsporum
Trichophyton
Epidermophyton

Each has preferences for different tissues

Question 8

Why can humans handle a large amount of fungi but only a small amount of bacteria (before we get very sick)

Answer 8

Fungi do not have PAMPS and do not stimulate the immune system efficiently

Question 9

List some examples of subcutaneous mycoses

Answer 9

Mycetoma (fungi + tumor) can have a bacterial cause of a fungal cause (eumycetoma). This is significant because the Rx is different for each cause - NO OVERLAP

Chromoblastomycosis

Phaeohyphomycosis`

Question 10

What are some yeast examples of Opportunistic mycoses?

Answer 10

1. Candidiasis: can be mucocutaneous, chronic mucocutaneous(in ppl with immunodeficiencies where they cannot clear infections) or systemic (septicaemia and death in neonates).
2. Cryptococcus: Inhaled disease and can be fatal if it gets in to the blood stream This is an AIDS defining illness that causes pulmonary infections and meningitis ( symptoms are slow but fatal). Agents that cause this disease are C. neoformans (most common - has a massive capsule) and C. gatti (near river reg gum trees)
3. Aspergillosis: Saprophytic (fungus ball grows in TB cavity), allergic or systemic

Question 11

What methods can you use to diagnose fungal infections?

Answer 11

Microscopy
Culture
Antigen detection (for cryptococcus - latex agglutination).
PCR (only some fungi)
Other: Mass-spec ("black box")

Question 12

How do you treat fungal infections?

Answer 12

Systemic: Polyenes (amphotericin B), triazoles, echinocandins, 5-flurocytosine

Topical: Polyenes, imidazoles

Question 13

What are the targets of anti-fungal agents?

Answer 13

They target ergosterol, a cytoplasmic membrane structure that is like cholesterol.
Polyenes affect integrity while triazoles affect the synthesis of ergosterol

Other tagets include nucleic acids - 5-flurocytosine (prodrug) affects DNA and RNA synthesis. It doesn’t affect our DNA because we don’t have the necessary enzyme to activate it.

Question 14

What is the treatment of systemic fungal infections

Answer 14

• Candida spp : fluconazole; amphotericin B;
caspofungin
• Cryptococcus : amphotericin B + 5-fluorocytosine
• Aspergillus : voriconazole; amphotericin B
• Dimorphic fungi : amphotericin B

Question 15

Treatment of dermatophytosis

Answer 15

Non-specific: reduce fungal load

Topical:
• terbinafine (“Lamisil”)
• clotrimazole (“Canesten”)
• amorolfine (“Loceryl”)

Oral:
• terbinafine
• fluconazole
• griseofulvin