Unit 2 - Mycology

General Information

What is Mycology?

Mycology is the scientific study of fungi, which includes yeasts (unicellular), molds (multicellular), and mushrooms (multicellular). Fungi are a diverse group of eukaryotic organisms that play essential roles in nature and human society.

Characteristics of Fungi

• Kingdom: Fungi (Eukaryotes)

• Over 100,000 species; about 200 are pathogenic to humans and animals

• Found in air, soil, and water

• Similar to algae but lack chlorophyll

• Mainly aerobic or facultative anaerobes

• Chemoheterotrophic: obtain carbon and energy from organic compounds by absorption

Benefits of Fungi

• Food Industry: Used in the production of alcoholic beverages, cheeses, breads, and truffles (high-value edible fungi).

• Antibiotics: Source of penicillin and other antibiotics.

• Decomposition: Decompose plant matter using enzymes like cellulase and pectinase.

• Medicinal Uses: Production of drugs such as Taxol (anticancer), statins (cholesterol-lowering), and cyclosporins (immunosuppressants).

• Genetic Engineering: Yeast cells are used to produce vaccines (e.g., Hepatitis B vaccine).

Undesirable Effects of Fungi

• Food Spoilage: Fungi can spoil food products.

• Plant Diseases: Cause significant agricultural losses (e.g., potato blight, Dutch elm disease, chestnut blight).

• Structural Damage: "Dry rot" damages buildings.

• Animal Diseases: White-nose syndrome in bats.

• Human Diseases: Mycoses (fungal infections).

Fungi vs. Bacteria

Feature	Bacteria	Fungi
Domain	Bacteria	Eukarya
Cell Type	Prokaryote	Eukaryote
Cellularity	Unicellular	Unicellular & Multicellular
Reproduction	Binary fission	Spores/Budding
Size	Smaller	Larger
Cell Wall	Peptidoglycan	Mannan, Chitin, Glucan
Cell Membrane	No sterols	Contains sterols

Growth Characteristics of Fungi

Fungi thrive in warm, moist environments but can also survive in dry conditions. They grow slower than bacteria, prefer acidic pH (around 5), and can tolerate high sugar or salt concentrations. Fungi grow best at room temperature and are susceptible to heat. They can metabolize complex carbohydrates such as lignin (wood).

Characteristics of Yeast

Structure and Reproduction

• Non-filamentous, oval, unicellular organisms

• Facultative: can perform respiration and fermentation

• Reproduce by budding (asexual); can produce up to 24 new cells

• Pseudohyphae: chains of cells formed when buds do not detach

Dimorphism

• Some fungi are dimorphic, meaning they can exist as either yeast or mold depending on temperature.

• At room temperature (25°C): mold-like growth

• At body temperature (37°C): yeast-like growth

Structural Characteristics of Molds

Vegetative Structures

• Thallus: The body of a mold, consisting of filaments

• Hyphae: Multicellular filaments that elongate at the tips

• Septa: Cross-walls dividing hyphae into cells

• Coenocytic hyphae: Hyphae without cross-walls

• Mycelium: A mass of hyphae visible to the naked eye

Reproductive Structures (Spores)

• Asexual Spores: Produced by mitosis; genetically identical to parent

• Types: Conidiospores (on conidiophores, e.g., Aspergillus, Penicillium) and Sporangiospores (within a sporangium, e.g., Rhizopus)

• Sexual Spores: Fusion of nuclei from two mating strains, followed by meiosis; types include zygospores, ascospores, and basidiospores

Laboratory Identification of Fungi

• Direct visualization of spores under a microscope

• Culturing on media with high sugar/salt, low pH, and at room temperature

• Biochemical and immunological testing

• Molecular analysis (e.g., PCR)

Toxin Production (Mycotoxins)

• Mycotoxins: Toxic compounds produced by fungi that can damage kidneys, liver, and nervous system

• Aflatoxin: Produced by Aspergillus species; found on peanuts and corn; carcinogenic and causes liver damage

• Ergot Poisoning: Caused by Claviceps purpurea on rye and grains; restricts blood flow and causes hallucinations

Fungal Infections (Mycoses)

Mycoses are classified based on the tissue involved. Fungal infections are often chronic due to the slow growth of fungi.

Superficial Mycoses

• Affect hair shafts and surface epidermal cells

• Example: Piedra—hard nodules on hair shafts, common in tropical climates

• Treatment: Shaving/cutting hair and topical antifungals

Cutaneous Mycoses

• Involve the epidermis, hair, and nails (dermatomycoses)

• Caused by keratinolytic fungi (dermatophytes): Trichophyton, Microsporum, Epidermophyton

• Lesions are dry, scaly, itchy, and have a red periphery

• Transmitted by direct contact or fomites; contagious

• Types: Tinea capitis (scalp), tinea unguium (nails), tinea cruris (groin), tinea pedis (feet)

• Treatment: Topical/oral antifungals; diagnosis by skin scraping, UV light, or culture

Subcutaneous Mycoses

• Occur beneath the skin, often from saprophytes in soil or vegetation entering through wounds

• Example: Sporotrichosis—caused by Sporothrix species; common in landscapers and farmers

• Treatment: Oral potassium iodide (KI)

Systemic Mycoses

• Deep infections affecting internal organs, usually acquired by inhalation of spores from soil fungi

• Not contagious; may resemble tuberculosis

• Treatment: Amphotericin B or fluconazole

• Examples: Histoplasmosis, Blastomycosis, Coccidioidomycosis (San Joaquin Valley Fever), Cryptococcosis

Opportunistic Mycoses

• Caused by fungi that are normally harmless but become pathogenic in immunocompromised individuals

• Examples: Aspergillosis (pulmonary, sinus, brain infections), Candidiasis (thrush, vaginal yeast infection, systemic infections)

• Treatment: Amphotericin B, miconazole, clotrimazole, mycostatin, nystatin, fluconazole

Additional info: Opportunistic mycoses are a major concern in patients with HIV/AIDS, cancer, diabetes, or those undergoing immunosuppressive therapy.