Medical Mycology Lecture 13 & 14

Introduction to Medical Mycology (Lecture 13 & 14)

• Fungi are eukaryotic organisms with true nuclei and nuclear membranes.
• Fungi have a rigid cell wall composed of chitin, β-D-glucan, mannan (Candida), and galactomannan (Aspergillus).
• The cell membrane contains ergosterol.
• Fungi also contain cytoplasm, nucleus, ribosomes, and mitochondria.

Morphology of Fungi

• Moulds (Filamentous Fungi): Branching filaments (hyphae) which may be septate or non-septate. A mass of hyphae is called a mycelium.

  • Examples: Aspergillus, Penicillium (septate), Mucor (non-septate).

• Yeasts: Unicellular, rounded or oval in shape. Reproduce by budding. Buds can separate from the mother cell or stay attached to form pseudohyphae.

  • Examples: Cryptococcus neoformans, Malassezia, Candida.

• Dimorphic Fungi: Grow as yeasts during body infection (at 37°C) and as moulds at room temperature (25°C).

  • Example: Histoplasma capsulatum.

Classification of Medical Fungi

• Primary Pathogenic Fungi (Endemic Mycosis): Cause disease in immunocompetent individuals.

  • Example: Histoplasma capsulatum (dimorphic fungus)

• Opportunistic Fungi: Cause disease in immunocompromised individuals.

  • Example: Candida.

Human Mycosis

• Definition: Disease caused by fungi.

• Types of Mycoses:

  • 1. Superficial Mycosis: Infection of outermost skin layers.

    • Example: Pityriasis versicolor (caused by Malassezia spp., skin normal flora).

  • 2. Cutaneous Mycosis: Infection extending deeper into the dermis, hair, and nails. Also known as Dermatophytosis (Tinea). Caused by keratinophilic filamentous fungi called dermatophytes.

    • Examples: Trichophyton, Microsporum, Epidermophyton.
      • Different types of tinea, based on affected body part:
        • Tinea capitis (scalp hair)
        • Tinea barbae (beard/moustache)
        • Tinea corporis (smooth skin)
        • Tinea pedis ("athlete's foot") (toe web and sole)
        • Tinea cruris (groin)
        • Tinea unguium (nails) (onychomycosis).

  • 3. Subcutaneous Mycosis: Infection involving subcutaneous tissue, muscle, and fascia.

    • Example: Mycetoma

  • 4. Systemic Mycosis: Infection involving many organ systems.

  • 5. Opportunistic Mycoses: Fungal infections in immunocompromised individuals.

    • Examples: Aspergillus (Allergic, Pulmonary, Invasive), Cryptococcosis (pigeon droppings, HIV patients), Mucormycosis (diabetic patients), Candidiasis (oral, vaginal, cutaneous, UTI).

Mycotoxicosis

• Poisoning of man and animals due to ingestion of food contaminated with fungal toxins.
• Examples:
  • Aflatoxin (Aspergillus flavus): Liver damage, hepatocellular carcinoma.
  • Ochratoxin (Aspergillus or Penicillium): Kidney damage.

Quiz Questions (Page 15)

• Q1: Ergosterol is a component of the fungal cell membrane.
• Q2: Tinea pedis is a fungal infection of the toe web and sole.