Eukaryotic_Parasite__Fungi

Introduction to Fungi

  • Definition: Fungi are heterotrophic eukaryotes that obtain nutrients from other organisms.

  • Cell Structure:

    • Cell wall made of chitin.

    • Cell membrane contains ergosterol (different from human cholesterol).

  • Roles in Ecosystem:

    • Principal decomposers in ecosystems.

    • Undergo alternation of reproductive cycles and secrete digestive enzymes.

Types of Fungi

1. Fleshy Fungi

  • Visible to the naked eye, often edible.

2. Microscopic Fungi

Yeasts

  • Reproduction primarily through budding.

    • Example: Saccharomyces cerevisiae.

  • Some yeasts reproduce through fission, e.g., Schizosaccharomyces pombe.

3. Molds

  • Grow in filamentous forms, referred to as hyphae.

    • Dimorphic fungi: Change between filamentous and non-filamentous forms based on environmental conditions.

Hyphae Types

  • Septate hyphae: Partition between cells with and without pores.

    • Septate with pores: Allows organelle and nutrient flow between cells.

    • Aseptate hyphae: Continuous hyphae structure, allowing cytoplasmic content flow.

Hyphae Functions

Vegetative Hyphae

  • Structures called rhizoids anchor and absorb nutrients.

Reproductive Hyphae

  • Carry spores, often referred to as aerial hyphae.

Types of Fungal Spores

Asexual Spores

  • Produced without mixing genetic material and are vital for fungal identification.

Types of Asexual Spores

  1. Sporangiospores: Enclosed in a sac (sporangium).

  2. Conidiospores: Not enclosed in a sac.

  3. Phialospores: Resemble a bouquet.

  4. Arthrospores: Formed from jointed fragments.

  5. Macronidia: Larger spores attached to a stem.

  6. Micronidia: Smaller clusters in tight spaces.

Sexual Spores

  • Produced through fusion of nuclei from two different fungi, indicative of sexual reproduction.

Types of Sexual Spores

  1. Zygospores: Formed through genetic exchange from two hyphae.

  2. Ascospores: Eight spores within a pod structure, sac-like.

  3. Basidiospores: Four spores produced on a basidium.

Major Fungal Phyla

Phylum Zygomycota (Conjugation Fungi)

  • Typically saprophytic molds with coenocytic or septate hyphae.

  • Asexual spore: Sporangiospores.

  • Example: Rhizopus stolonifera (found in rotting strawberries).

Phylum Ascomycota (Sac Fungi)

  • The largest and most diverse phylum.

  • Includes molds with porous septate hyphae and various yeasts.

  • Asexual spore: Conidiospores; sexual spore: Ascospores.

Phylum Basidiomycota (Club Fungi)

  • Capable of producing a fruiting body.

  • Asexual spores vary; sexual spores: Basidiospores.

Fungal Pathogenesis

Mycosis

  • Fungal infections characterized by their virulence and ability to cause disease.

Types of Mycosis

  1. Systemic Mycosis: Access through the bloodstream.

  2. Subcutaneous Mycosis: Access to subcutaneous tissue.

  3. Dermatomycosis: Affects skin surfaces.

  4. Superficial Mycosis: Infections on the surface of the skin.

  5. Opportunistic Mycosis: Infections occurring in immunocompromised hosts.

Diagnostic Approaches for Mycosis

  • Techniques include:

    • Sputum testing, blood tests, tissue biopsies, and special stains.

    • KOH wet mounts for quick identification of fungal elements.

Key True Pathogenic Fungi

  1. Coccidioidomycosis (Valley Fever)

    • Agent: Coccidioides immitis (Ascomycetes).

    • Symptoms: 60% asymptomatic; 40% cold-like symptoms.

    • Can lead to disseminated forms in immunocompromised hosts.

  2. Sporotrichosis (Rose Gardener's Disease)

    • Agent: Sporothrix schenckii (Ascomycetes).

    • Enters through traumatized skin, causing local lesions and lymphatic involvement.

Common Fungal Infections

Dermatomycosis (Ringworm)

  • Caused by agents like Trichophyton sp., Microsporum sp., and Epidermophyton.

  • Entry through direct contact, infecting the epidermis with keratinase production.

Candidiasis (Opportunistic Mycosis)

  • Caused by Candida albicans.

  • Most common opportunistic pathogen; can result in vulvovaginal infections and candidiasis in the oral cavity.

  • Risk factors include antibiotics, pregnancy, and diabetes.

Cryptococcosis

  • Agent: Cryptococcus neoformans (Basidiomycetes).

  • Enters through respiration and can disseminate in immunocompromised individuals.

Aspergillosis

  • Agent: Aspergillus species (Ascomycetes).

  • Primarily a respiratory infection; can form fungal balls known as aspergillomas in the lungs.