chapter 5

Chapter 5: Eukaryotes in Microbiology

Overview of Mycology

• Mycology: Study of fungi.

  • Structure and growth requirements of fungi.

Key Terms

• Mycosis: Fungal infection categorized into several types:

  • Systemic: Deep within the body.

  • Subcutaneous: Just under the skin.

  • Cutaneous: Affecting the skin, hair, or nails.

  • Superficial: Only the top surface of the skin.

  • Opportunistic: Infections that occur under certain conditions where the immune system is compromised.

Characteristics of Fungi

• Fungi are eukaryotic (have a nucleus and membrane-bound organelles).

• Cell wall composition: Differ from prokaryotes; do not contain peptidoglycan.

• Mostly multicellular; yeasts are unicellular.

• Chemoheterotrophs: Acquire nutrients through absorption.

• Osmotic pressure: More resistant to high sugar/salt concentrations compared to bacteria.

Types of Fungi

• Lichens:

  • Symbiotic relationship between a photosynthetic organism (green algae or cyanobacteria) and fungus.

  • Sensitive to pollution; indicators of ecological health.

• Molds:

  • Multicellular fungi; structure is primarily hyphae.

  • Hyphae types:

    • Septate: Individual cells separated by cell walls.

    • Non-septate: Continuous strands with multiple nuclei.

  • Vegetative hyphae: Nutrient acquisition (roots equivalent).

  • Aerial hyphae: Reproduction and visible growth.

  • Mycelium: Visible mass of hyphae, can be called aerial mycelium (above agar) or vegetative mycelium (below agar).

• Yeasts:

  • Unicellular fungi, reproduce asexually (budding).

  • Can perform aerobic respiration or fermentation.

Dimorphic Fungi

• Exhibit two forms of growth based on temperature:

  • Yeast form at 37°C (human body temperature).

  • Mold form at 25°C (room temperature).

  • Example: Histoplasma capsulatum, causes severe respiratory infections.

Overview of Protists

• Kingdom Protista: Eukaryotic organisms not classified as plants, animals, or fungi.

• Plant-like Protists: Photosynthetic organisms (e.g., algae).

  • Types: Green algae, brown algae, red algae.

  • Example: Kelp (multicellular) in marine environments.

• Fungus-like Protists:

  • Water molds and slime molds (e.g., Phytopthora infestans causing potato blight).

  • Do not cause disease in humans but can impact agriculture.

• Animal-like Protists (Protozoans):

  • Single-celled organisms with characteristics similar to animals.

  • Examples of important protozoan parasites:

    • Trypanosoma brucei: Causes African sleeping sickness, transmitted by the tsetse fly.

    • Trypanosoma cruzi: Causes Chagas disease, transmitted by the kissing bug.

    • Giardia lamblia: Causes gastrointestinal issues, known as beaver fever.

    • Naegleria fowleri: Can cause fatal brain infections, found in warm freshwater.

    • Cryptosporidium: Opportunity infection in immunocompromised individuals; resistant to chlorine.

    • Plasmodium: Causes malaria, requires mosquitoes as a vector for reproduction.

Parasitology

• Parasitology: Study of parasites, which benefit at the expense of the host.

• Main categories of parasites:

  • Unicellular Parasites (Protozoans): Lead to various diseases.

  • Worms (Helminths): Flatworms (e.g., flukes, tapeworms) and roundworms.

  • Ectoparasites: Live on the surface of hosts (e.g., ticks, fleas).

Helminths

• Break into:

  • Flatworms (e.g., Schistosoma haematobium): Have two hosts—snail (intermediate) and human (definitive).

    • Can cause chronic illnesses and live up to thirty years in the host.

  • Tapeworms (e.g., Taenia saginata and Taenia solium):

    • Scolex: Anterior segment with suckers for attachment.

    • Taenia saginata (beef tapeworm) vs. Taenia solium (pork tapeworm).

    • Taenia solium can lead to neurocysticercosis if eggs are ingested.

Vectors and Hosts

• Vectors: Organisms such as mosquitoes or ticks that carry certain parasites.

  • Example: Tsetse fly for Trypanosoma, mosquitoes for Plasmodium.

• Definitive Host: Where the parasite reproduces sexually (e.g., mosquito for Plasmodium).

• Intermediate Host: Where the parasite reproduces asexually (e.g., humans for Plasmodium).

Additional Concepts

• Encystment: Protective stage allowing survival in adverse conditions.

• Schizogony: Multiple fission for rapid population increase (example: Plasmodium).

• Hermaphroditism: Presence of both male and female reproductive organs in a single parasite (e.g., tapeworms).