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.