fungi

• Mycology


  Study of fungi
• Fungi


  Group of eukaryotic microorganisms, some of which are capable of causing superficial, cutaneous, subcutaneous, or systemic disease
• Fungi

  • Possess chitinous cell walls
  • Plasma membranes containing ergosterol
  • 80S rRNA
  • Microtubules composed of tubulin
• General Structure of Fungi


  1. Cell wall - stratified structure consisting of chitinous microfibrils embedded in a matrix of small polysaccharides, proteins, lipids, inorganic salts, and pigments that provides skeletal support and shape to the enclosed protoplast

  2. Major polysaccharides of the matrix consist of: noncellulosic glucans such as glycogen-like compounds, mannans (polymers of mannose), chitosan (polymers of glucosamine), galactans (polymers of galactose)

  3. Cell walls may contain lipid, protein, chitosan, acid phosphatase, α-amylase, protease, melanin, and inorganic ions such as phosphorus, calcium, and magnesium
• Plasma Membrane


  • Similar to mammalian plasma membranes, differing in having the nonpolar sterol ergosterol, rather than cholesterol, as the principal sterol
  • Regulates the passage of materials into and out of the cell by being selectively permeable
  • Membrane sterols provide structure, modulation of membrane fluidity, and possibly control of some physiologic events
  • Contains primarily lipids and protein, along with small quantities of carbohydrates
  • The major lipids are the amphipathic phospholipids and sphingolipids that form the lipid bilayer
• Microtubules


  • Composed of the protein tubulin
  • Long, hollow cylinders approximately 25 nm in diameter that occur in the cytoplasm as a component of larger structures involved in the movement of organelles, chromosomes, nuclei, and Golgi vesicles containing cell wall precursors
  • Principal components of the spindle fibers, which assist in the movement of chromosomes during mitosis and meiosis
  • Griseofulvin, which is used to treat dermatophyte infections, binds with microtubule-associated proteins involved in the assembly of the tubulin dimers. By interfering with tubulin polymerization, griseofulvin stops mitosis at metaphase
• Nucleus


  • Bounded by a double nuclear envelope and contains chromatin and a nucleolus
  • Variable in size, shape, and number
• General Features of Fungi

  • Can occur as yeasts
  • Can occur as molds
  • Can occur as a combination of both forms
• Yeasts


  Single-celled forms that reproduce by budding
• Molds


  Form multicellular & long filaments - hyphae
• Dimorphic fungi

  • Grow as yeasts or spherules in vivo, as well as in vitro at 37°C, but as molds at 25°C
  • Dimorphism is regulated by factors such as temperature, CO2 concentration, pH, levels of cysteine or other sulfhydryl-containing compounds
• Fungal reproductive structures

  • Asexual structures are referred to as anamorphs
  • Sexual structures are known as teleomorphs
  • The whole fungus is known as the holomorph
• Fungi can use a number of different carbon sources to meet their carbon needs for the synthesis of carbohydrates, lipids, nucleic acids, and proteins
• Oxidation of sugars, alcohols, proteins, lipids, and polysaccharides provides fungi with a source of energy
• Fungi require a source of nitrogen for synthesis of amino acids for proteins, purines and pyrimidines for nucleic acids, glucosamine for chitin, and various vitamins
• Fungi


  Heterotrophs that rely on carbon fixed by other organisms for metabolism
• Carbon sources used by fungi

  • Carbohydrates
  • Lipids
  • Nucleic acids
  • Proteins
• Fungi obtain energy

  1. Oxidation of sugars

  2. Oxidation of alcohols

  3. Oxidation of proteins

  4. Oxidation of lipids

  5. Oxidation of polysaccharides
• Fungi require a source of nitrogen for synthesis of amino acids, purines, pyrimidines, glucosamine, and various vitamins
• Fungi as infectious agents

  • Molds and yeasts are widely distributed in air, dust, fomites and normal flora
  • Humans are relatively resistant
  • Fungi are relatively nonpathogenic
  • Of the 100,000 fungal species, only 300 have been linked to disease in animals
  • Fungi are the most common plant pathogens
  • Human mycoses are caused by true fungal pathogens and opportunistic pathogens
• Trichosporon Asahii can cause white piedra
• Piedra Hortae can cause Black piedra
• Malessezia Furfur can cause tinea versicolor which affects the trunk, neck, face , arms (An-an)
• Trichophyton can cause:

  • Tinea barbae which affects the beard area
  • Tinea Capitis Affects the scalp and hair ( Dandruff)
  • Tinea Cruris affects groin and buttocks ( Jock itch)
  • Tinea pedis affects the feet ( Alipunga)
  • Tinea unguium Affects the nails ( Oncomycosis)
  • Tinea Corporis Affects the smooth or bare are of the skin ( Ring worm)
• Superficial Mycoses- Localized the skin, the hair and the Nails
• Cutaneous mycoses( Dermatomycoses) - Affects hair, skin and nails
• Subcutaneous mycoses- Beneath the skin
• Systemic mycoses - deep within the body
• Opportunistic mycoses- caused by normal microbiota or fungi that are normally not pathogenic