Lecture 4: Fungi

Question 1

Morphological forms

Answer 1

1. Yeasts - unicellular
   - typically round/oval
   - asexual repro (budding); mother producing daughter cells
   - pseudohyphae
2. Moulds - multicell
   - filamentous/tubular structures (hyphae); permanence and branching
   - arhtrospores & chlamydiospores only found in true hyphae
   - Sexual & Asexual reproduction (spores)
   - Gram stain all appear Gram +ve but much larger than bacteria

Question 2

Mycelium

Answer 2

• intertwined mat of hyphae
• looks like cotton on white bread
• 2 portions
  1. Vegetative: attached to substrate/penetrates to obtain substrate
  2. Reproductive: represented by aerial structures (cottony); asexual reproduction propagules (conidia)

Question 3

Dimorphic fungi

Answer 3

• Same organism exhibits 2 different forms -> mycelial (sub-physiological temp) & yeast (optimal temp) forms
• most fungi are dimorphic
• Note: most important factor for determining dimorphic state is temp.

EXCEPTIONS

• Aspergillus sp.: always in mycelial phase (mould phase)
• Torula sp.: exists only as yeast

Question 4

Fungal features

Answer 4

• no structures of locomotion
• no capsules except Cryptococcus neoformans
• cell wall thick & rigid, no peptidoglycan
• cytoplasmic membrane contains ergosterol (antifungal drugs)

Question 5

Fungal classification

Answer 5

Eumycota: 5 subdivisions (4 pathogenic to humans)

• Zygomycotina: bread mould, reproduce sexually & asexually (asexual spores in sporangium), not primary pathogens (opportunistic) Ex. water molds
• Ascomycotina: skin infections, aspergillus, yeast and moulds, produce sexual (ascospores) and asexual (conidia) spores
• Basidomycotina: sexual spores (basidiospores), mushrooms & puffballs, F. neoformans, GI lectures
• Deuteromycotina (fungi imperfecti): reproduce asexually, Epidermophyton sp., microsporium sp, Trichophyton sp., Candida

Question 6

Describe the classification of human mycoses

Answer 6

• supericial: Malassezia furfur; initially pulmonary -> disseminated
• cutaneous: microsporium, trichophyton
• sub-q: Sporothrix schenkii
• systemic/endemic: Histoplasma, Coccidoides
• opportunistic: Aspergillus, Candida

Question 7

Most fungi are dimorphic with these exceptions:

Answer 7

• Aspergillus (mould)
• Torula (yeast)