Mycology intro

• Mycology


  The study of fungi
• Fungi


  • Their natural habitat is the environment
  • Most are obligate aerobes
  • They are eukaryotes with a nuclear membrane, mitochondria, endoplasmic reticulum, and 80s ribosomes
• Uses of fungi


  • Bread, cheese, wine and beer
  • Spoilage of fruits, grains, vegetables and jams
  • Important human pathogens
• Fungal cell walls


  Made of glucans, mannans, chitin, and chitosan
• Fungal cell membranes


  Have sterols (ergosterol)
• Hyphae


  Long, branching, filamentous cells that are connected end-to-end
• Mycelium


  An intertwined mass of hyphae that forms the mould colony
• Conidia


  Asexual spores borne externally on hyphae
• Conidiophore


  Specialized hyphae
• Sporangium


  A spherical sack in which spores are produced
• Germ-tube


  The initial hyphal outgrowth of a germinating spore or yeast
• Pseudohyphae


  Continued elongation of the parent cell before it buds
• General properties of fungi

  • Eukaryotic
  • Have ergosterol in the cell membrane
  • Have 80S ribosomes
  • Have a rigid cell wall made of chitin
  • Lack chlorophyll
  • Obtain nutrients as saprophytes or parasites
  • Typically not motile
  • Typically reproduce asexually and/or sexually by producing spores
  • Grow either reproductively by budding or non-reproductively by hyphal tip elongation
• Fungal forms


  • Moulds
  • Yeast
  • Dimorphic fungi
• Moulds


  • Multicellular fungi that form branching filaments called hyphae
  • A mass of hyphae (branching hyphae) collectively make up the mycelium
  • Have two kinds of hyphae: non-septate (coenocytic) and septate
• Yeasts


  • Round, oval or elongate unicellular fungi
  • Reproduce by simple budding to form blastoconidia on the surface of the parent cell
  • Some produce chains of elongated cells (pseudohyphae) or true hyphae
  • Some pathogenic yeasts form a capsule, forming mucoid colonies
• Dimorphic fungi


  • Able to grow as yeasts or moulds depending on environmental conditions and temperature
  • The yeast form is found in infected tissue and the filamentous form is found in the soil
• Modes of fungal reproduction

  • Asexual reproduction (conidia/conidiospores, sporangiospores, arthrospores, chlamydospores, blastoconidia)
  • Sexual reproduction (ascospores, basidiospores, zygospores)
• Classes of medically important fungi

  • Ascomycetes
  • Basidiomycetes
  • Deuteromycetes
  • Zygomycetes
• Factors contributing to fungal pathogenicity

  • Ability to adhere to host cells using glycoproteins
  • Capsules
  • Ability to acquire iron from red blood cells
  • Enzymes (e.g. keratinase, elastase, collagenase)
  • Mycotoxin production
  • Thermal dimorphism
  • Cell-mediated immunity resistance
• Most human fungal infections are caused by saprophytes
• Ways fungal infections can be acquired

  • Inhalation
  • Ingestion
  • Traumatic implantation
• Many fungal diseases have a worldwide distribution, and some are endemic
• Types of fungal diseases

  • Mycoses
  • Mycotoxicoses
  • Allergies
• Types of mycoses


  • Superficial mycoses
  • Subcutaneous mycoses
  • Systemic mycoses
• Types of superficial mycoses

  • Dermatophytoses
  • Superficial candidiasis
• Types of subcutaneous mycoses

  • Mycetoma
  • Chromoblastomycosis
  • Sporotrichosis
• Systemic mycoses result from inhalation of air-borne spores and initially cause pulmonary infection, which may then disseminate to other organs
• Types of mycotoxicoses


  • Aflatoxins
  • Hepatoxins
  • Vascular and neurologic toxins
• Allergies to fungal spores, especially Aspergillus, can cause asthmatic reactions
• Diagnostic methods for fungal infections

  • Clinical observation
  • Microscopy
  • Culture
  • Serology
  • PCR
• Specimen types for diagnosis

  • Skin scales, nail clippings, scalp scrapings, mucous membrane swabs (for superficial mycoses)
  • Scrapings, crusts, aspirated pus, biopsies (for subcutaneous mycoses)
  • Appropriate specimens from affected sites (for systemic mycoses)
• Antifungal agents


  • Targeting the fungal cell wall
  • Targeting the fungal cell membrane (sterols, ergosterol biosynthesis)
  • Targeting fungal nucleic acids
• Classification of fungal infections by depth

  • Superficial
  • Cutaneous
  • Subcutaneous
  • Systemic
• Specimens for diagnosis of fungal infections


  • Specimens from appropriate sites
• Diagnosis of fungal infections

  1. Direct microscopy

  2. Partial digestion of tissue with 10-20% potassium hydroxide(KOH)

  3. Wet mount

  4. Histology

  5. Culture on Sabouraud's dextrose agar(SDA) and 4% malt extract agar, incubate at 25-30°C and at 37°C
• Antifungal agents target


  • Cell membrane
  • Nucleic acids
  • Cell wall
• Fungal cell wall


  Composed of chitin, (1,3)-ẞ-glucan, > (1,6)-ẞ-glucan, mannan
• Fungal cell membrane


  Contains ergosterol
• Enzymes involved in ergosterol biosynthesis

  • Fks1
  • Fks2
  • Erg11
  • Cyp51A/Cyp51B