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Important points about Fungus

  • Group of non-motile eukaryotic organisms which exist as saprophytes, parasites or commensals
  • The cells possess rigid cell wall composed of chitin (polymer of N-acetylglucosamine)
  • Cell membrane which surrounds the cytoplasm contains sterols (ergosterol)
  • The cytoplasm contains true nuclei with nuclear membrane, mitochondria, 80 S ribosomes, food reserves (fat, oil or glycogen)
  • Fungi may be unicellular or multicellular. They divide asexually, sexually or by both processes 

A. Systematic classification

  1. Phylum: Thallophyta
    1. Algae (possess chlorophyll)
    2. Fungi (chlorophyll absent) 

B. Four classes (according to type of sexual spore formed)

  1. Zygomycetes (zygospores)
  2. Ascomycetes (ascospores)
  3. Basidiomycetes (basidiospores)
  4. Deuteromycetes-Lack known sexual state. Also called as Fungi Imperfecti (Most medically important fungi belong to this group) 

C. Morphological classification


1. Yeasts

  1. Reproduce asexually by budding or fission
  2. Round or oval unicellular fungi
  3. Form moist or mucoid colonies

e.g.: Saccharomyces cerevisiae, Cryptococcus neoformans


2. Yeast-like

  1. Formation of pseudohyphae (chains of elongated cells having constriction at the septa)
    e.g.: Candida spp. 

3. Molds

  1. Produce branching filaments called hyphae
  2. Hyphae may be septate or nonseptate (coenocytic)
  3. Tangled mass of hyphae is called as mycelium
  4. In culture medium part of the mycelium projecting above the surface is called as aerial mycelium and part growing in the medium is called as vegetative mycelium
    e.g.: Aspergillus spp., Penicillium spp., dermatophytes, Mucor spp. etc. 

4. Dimorphic fungi

  1. Yeast form in the host tissue and in-vitro at 37°C on enriched media
  2. Mould form in-vitro at 25°C
i. e.g.: Sporothrix schenckii, Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis, Penicillium marneffei

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