GENERAL CHARACTERISTICS OF FUNGI

• Yeast

  • Single vegetative cells
  • Smooth, creamy, bacteria-like colony
  • No aerial hyphae
  • Mode of replication: budding / binary fission = maturation of the bud to a blastoconidium
• Moulds

  • Fuzzy / wooly appearance
  • Have Mycelia, composed of hyphae = many long strands of tube-like structures
• Aerial Mycelia / Hyphae

  • Extend to the surface
  • Support the reproductive structures = conidia
• Vegetative Mycelia / Hyphae

  • Extend downward
  • Absorb nutrients
• Microscopic appearance of Moulds

  • Antler hyphae / Favic chandelier : branching tips, "moose antlers"
  • Racquet hyphae : enlarged, club-shaped areas
  • Spiral hyphae : tight coils
  • Pectinate bodies : comb-like structures
  • Rhizoids : root-like structures
  • Septate hyphae : with frequent cross-walls perpendicular to the outer walls of the hyphae
  • Sparsely septate : few cross-walls, irregular intervals
  • Aseptate : absence of septations;
• Hyaline vs Phaeoid Fungi

  • Identified based on pigmentation due to presence of melanin on cell wall
  • Hyaline / Moniliaceous hyphae : non-pigmented, lightly pigmented
  • Phaeoid / Dematiaceous hyphae : darkly pigmented
• Fontana-Masson tissue stain

  • Stains specifically melanin
  • Phaeoid hyphae = brown
• Dimorphism

  • Ability of a fungi to exist in 2 forms depending on growth condition

  Yeast Phase

  • Spherule, tissue phase
  • Growth condition: in vivo or at 37C, increased Co2

  Mould Phase

  • Growth condition: at 22C to 25C, ambient air
• Polymorphism

  • Both yeast and mould form in the same culture
  • Example: Exophiala spp.
• Asexual / "Imperfect" Reproduction

  • Formation of a conidium after mitosis
  • Done by budding of conidiogenous cells

  Phialides = vase-like structures; produce phialaconidia

  Annelides = ringed-structures; produce anelloconidia

  Arthroconidia = by fragmentation of fertile hyphae
• Results of conidia formation

  • Macroconidia = large & multicellular
  • Microconidia = small & unicellular
• Sexually / "Perfect" Reproduction

  • Joining of 2 compatible nuclei in meiosis

  Teleomorph = fungi that reproduces sexually

  Anamorph = telomorph that can also reproduce asexually

  Synanamorph = more than 1 anamorph is present for the same teleomorph
• Types of Specialized Sexual Spores

  • Ascospores = sac fungi; contained in sac-like ascus
  • Zygospores = conjugation fungi; large spore with thick wall; fusion of 2 identical cells
  • Basidiospores = club fungi; spores produced in a basidium; point of attachment is sterigma
• Mucorales

  • Traditionally zygomycota or glomerulomycota
  • Rapid-growing, soil inhabitants
  • Opportunistic pathogens
  • Morphology: gray-white aerial mycelium with hyaline, sparsely septate hyphae
  • Reproduction: asexual; produces sporangiospores
• Member genera of Mucorales

  1. Lichtheimia
  2. Mucor
  3. Rhizopus
  4. Rhizomucor
• Ascomycota

  • Microscoporum spp., Trycophython spp. = cutaneous
  • Pseudallescheria boydii = subcutaneous-eumycotic mycetoma
  • Saccharomyces spp., Candida spp. = yeast
  • Blastomyces spp., Coccidioides spp. = systemic
  • Reprodiction: sexual; production of ascospores within ascus
• Basidiomycota

  • Filobasidiella neoformans = teleomorph form of Cryptococcus neoformans
  • Presence of clump connections
• Deuteromycota

  • "Fungi imperfecti"
  • Contains largest number of clinically significant agents of mycoses
  • No mode of sexual reproduction identified