Q1. Write a detailed account of the general properties and classification of fungi. General Properties: - E
TOPIC 1: INTRODUCTION TO MYCOLOGY (Lecture 1) --- Q1. Write a detailed account of the general properties and classification of fungi. General Properties: Eukaryotic — cells contain membrane-bound organelles Have a rigid cell wall made of chitin Lack chlorophyll — cannot photosynthesize Chemoheterotrophs — require organic compounds for carbon and energy Have ergosterols in their membranes — regulate permeability and fluidity Possess 80S ribosomes No obligate anaerobes — all require water and oxygen Obtain nutrients as saprophytes (decaying matter) or parasites (living matter) Reproduce asexually and/or sexually by producing spores Food storage in the form of lipids and glycogen Grow reproductively by budding or non-reproductively by hyphal tip elongation Classification based on Sexual Reproduction: Zygomycetes — sexual spores called zygospores Ascomycetes — sexual spores called ascospores, produced in asci Basidiomycetes — sexual spores called basidiospores, produced on basidia Deuteromycetes (Fungi Imperfecti) — no known sexual spores demonstrated Classification based on Morphology: Moulds — filamentous; made of hyphae; e.g. Aspergillus Yeasts — unicellular; reproduce by budding; e.g. Cryptococcus Yeast-like — produce pseudohyphae; e.g. Candida albicans Dimorphic — exist in two forms depending on temperature; yeast at 37°C, mould at 25°C; e.g. Histoplasma capsulatum --- Q2. Describe the morphology of moulds, yeasts, and dimorphic fungi. Moulds: Made of cylindrical tube-like structures called hyphae Mass of hyphae = mycelium Hyphae can be branched or unbranched Septate hyphae — have cross walls (septa) with pores; cytoplasm is continuous; damage to one compartment does not kill the whole strand Aseptate hyphae — no septa; more primitive; damage kills the entire strand All moulds are septate except Zygomycetes (Rhizopus, Mucor) All fungal hyphae tend to be coenocytic (multinucleate) Yeasts: Unicellular; spherical or ellipsoid Reproduce by budding — forms blastospores (blastoconidia) Buds that fail to detach elongate to form pseudohyphae (e.g. Candida albicans) Candida albicans can also produce true hyphae (germ tube) Some yeasts produce a capsule e.g. Cryptococcus, Blastomyces True yeasts like Saccharomyces do not produce pseudohyphae Dimorphic Fungi: Exist as yeast in infected tissue and when cultured at 37°C Exist as mould in natural habitat and when cultured at 25°C Examples: Blastomyces dermatitidis, Histoplasma species, Paracoccidioides brasiliensis, Coccidioides immitis --- Q3. Describe the types of asexual spores produced by fungi. Conidia/Conidiospores — small single-celled microconidia or large multicellular macroconidia; formed at the tip of hyphae Sporangiospores — single-celled spores found within a sac called a sporangium at the tip of a sporangiophore Arthrospores — spores formed from fragmented hyphae Chlamydospores — spores with very thick walls; resistant forms Blastoconidia (Blastospores) — formed through a budding process; seen in yeasts --- TOPIC 2: FUNGAL PATHOGENESIS (Lecture 2) --- Q4. Describe the pathogenesis of fungal infections, including virulence factors and host defenses. Pathogenesis: Most fungi are saprophytic; infection in humans is a chance event when conditions are favourable Except for dimorphic fungi and dermatophytes (primary pathogens), most fungi are opportunistic The human body is generally hostile to fungi Interplay between fungal virulence factors and host defenses determines whether disease occurs Infection depends on inoculum size and host immunity Virulence Factors of Fungi: Adhesion to host cells via cell wall glycoproteins Capsule production — resists phagocytosis (e.g. Cryptococcus) Secretion of enzymes — keratinase, elastase, collagenase — damage host tissue Ability to acquire iron from red blood cells (e.g. Candida albicans) Resistance to killing by phagocytes (e.g. dimorphic fungi) Secretion of mycotoxins Thermal dimorphism — allows survival and pathogenicity at body temperature Blocking cell-mediated immune defenses Host Defense Factors: Physical barriers — skin and mucous membranes Fatty acid content of the skin — antifungal pH of skin, mucosal surfaces and body fluids Epithelial cell turnover — removes colonizing fungi Normal flora — competes with fungi, keeps them commensal Chemical barriers — secretions, serum factors Body temperature 37°C — most fungi are mesophilic and cannot grow at this temperature Phagocytic cells — PMNs (effector cells) and macrophages/monocytes (professional phagocytes) --- Q5. Describe immunity to fungal infections (innate and acquired). Innate (Non-specific) Immunity: Physical barriers — skin and mucous membranes pH and body temperature Serum factors Normal flora Phagocytic cells — PMNs, monocytes and macrophages Acquired Immunity: Both humoral and cell-mediated immunity (CMI) are mounted CMI is the mainstay of host defense because fungi reside intracellularly Cell-Mediated Immunity (CMI): Non-specific arm — PMNs and macrophage