Introduction to Mycology

Introduction to Mycology Dr. Sundes Sultan Introduction to Mycology • Mycology is the study of fungi – • Yeast • Mold Yeasts and molds • Have different structural and reproductive characteristics • Yeast are unicellular, nucleated rounded fungi while molds are multicellular, filamentous fungi • Yeast reproduce by a process called budding while molds produce spores to reproduce • Some yeast are opportunistic pathogens in that they cause disease in immuno-compromised individuals • Yeast are used in the preparation in the variety of foods Basic terms as they relate to mycology: • Hypha (hyphae plural) - fundamental tube-like structural units of fungi. • Septate - divided by cross walls. • Aseptate - lacking cross walls. • Mycelium - a mass (mat) of hyphae forming the vegetative portion of the fungus. • Aerial - growing or existing in the air. • Vegetative - absorbs nutrients. • Fertile - bears conidia (spores) for reproduction. Basic Terms (continued) Sporulation & Spores - preferred terms when there is a merging of nuclear material. Self- fertile are termed homothallic. Mating types are termed heterothallic. • Sexual spores - exhibit fusion of nuclei. • Ascospore - spore formed in a sac-like cell known as an ascus. Often eight (8) spores formed. (Ascomycetes) Basic Terms (continued) • Basidiospore - sexual spore produced on a specialized club-shaped structure, called a basidium. (Basidiomycetes) • Zygospore - a thick-walled spore formed during sexual reproduction (Phycomycetes) Sporulation & Spores (continued) • Asexual spores - most common type. • Conidia - asexual fungal spores borne externally in various ways from a conidiophore; often referred to a macroconidia (multicellular) and microconidia (unicellular). • Arthroconidium (Arthrospore) - special type of asexual spore formed by disarticulation of the mycelium. Sporulation & Spores (continued) • Chlamydospore - thick-walled asexual spore formed by direct differentiation of the mycelium (concentration of protoplasm and nutrients). • Blastoconidia (Blastospore) - asexual spore formed from a budding process along the mycelium or from another blastospore Sporulation & Spores (continued) • Sporangiospore - an asexual spore contained in a sporangium at the end of a sporangiophore. • Thallospore - asexual spore produced on a thallus (hypha). Fungi Fungi - includes molds and yeasts. Molds - exhibit filamentous type of growth. Yeasts - exhibit pasty or mucoid form of fungal growth. • 50,000 + valid species • Fungi stain gram positive, and require oxygen to survive. Fungi • Fungi are eukaryotic, containing a nucleus bound by a membrane, an endoplasmic reticulum, and mitochondria. (Bacteria are prokaryotes and do not contain these) • Fungi are heterotrophic like animals and most bacteria; requiring organic nutrients as a source of energy. (Plants are autotrophic) Fungi Fungi are dependent upon enzyme systems to derive energy from organic substrates. • Saprophytes - live on dead organic matter. • parasites - live on living organisms. Fungi are essential in recycling of elements, especially carbon. Fungi • Fungi serve both beneficial and harmful roles in our environment • Molds used in the production of cheeses and also serve an antimicrobial purpose (penicillin). • Molds can be opportunistic infections in debilitated and immunosuppressed individuals. Classifications of Fungi: • Geographic grouping - where they exist. • Epidemiologic grouping - how organism is transmitted. • Taxonomy grouping - according to morphologic and cultural characteristics. • Topographic Grouping - type of mycosis produced. Topographic Grouping of Fungi: • Superficial - Confined to the outermost layers of the skin and hair. No host cellular or inflammatory response due to organisms being remote from living tissue. Essentially no pathology; the disease is recognized purely on cosmetic basis. • Cutaneous - in the keratin of the skin, nails, and hair. These organisms prefer non-living cornified layers. The disease is called a dermatophytosis or dermatomycosis. Host response is patchy scaling or eczema eruptions. They are classified according to the area of the body that is involved Topographic Grouping of Fungi: • Subcutaneous - Involve the deeper layers of skin and often muscle tissue. Man is an accidental host following inoculation of fungal spores via some form of trauma. This type of infection is often identified by the presence of a characteristic tissue reaction or granule. • Systemic - Attack the deep tissues and organ systems; often creating symptoms that resemble other diseases. Categories of systemic disease: • Those caused by truly pathogenic fungi with the ability to cause disease in the normal human host when the inoculum is of sufficient size (Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides braziliensis). Categories of systemic disease: • Those caused by opportunistic fungi, low virulence organisms, which require the patient's defenses to be lowered before the infection is established (Aspergillus spp. Candida albicans, Cryptococcus neoformans). Role of fungi in the economy: • Industrial uses of fungi - • Mushrooms. (Class Basidiomycetes) • Truffles. (Class Ascomycetes) • Natural food supply for wild animals. • Yeast as food supplement, supplies vitamins. • Penicillium - ripens cheese, adds flavor (roquefort, etc.). • Fungi used to alter texture, improve flavor of natural and processed foods. Role of fungi in the economy: • Fermentation • Fruit juices (ethyl alcohol). • Saccharomyces cerevisiae - brewer's and baker's yeast. • Fermentation of industrial alcohol, fats, proteins, acids, etc. • Antibiotics - • First observed by Fleming; noted suppression of bacteria by a contaminating fungus of a culture plate. Fungi advantages and disadvantages Advantages: • Great decomposers • Recycles nutrients Disadvantages: • Takes over spoiled food • Takes over moist areas • Allergic reactions-respiratory problems. • Cause irritations like ringworm, athlete’s foot, nail fungus Disadvantages examples • Ring worm: is a contagious itching skin disease occurring in small circular patches, caused by any of a number of fungi and affecting chiefly the scalp or the feet. Disadvantages examples • Athlete’s foot — also called tinea pedis — is a contagious fungal infection that affects the skin on the feet. It can also spread to the toenails and the hands. The fungal infection is called athlete’s foot because it’s commonly seen in athletes. • Athlete’s foot isn’t serious, but sometimes it’s hard to cure. If you have diabetes or a weakened immune system and suspect you have athlete’s foot, you should call your doctor right away. Disadvantages examples • Nail fungus: infections are common infections of the fingernails or toenails that can cause the nail to become discolored, thick, and more likely to crack and break. Importance of Medical Mycology • Fungi cause more than a billion skin infections, more than 100 million mucosal infections • 10 million serious allergies and more than a million deaths each year. • Global mortality owing to fungal infections is greater than for malaria and breast cancer and is equivalent to that owing to tuberculosis (TB) and HIV. • These statistics evidence fungal infections as a major threat to human health worldwide. The Immunosuppressed Patient: • AIDS • Drugs - immunosuppressant drugs used in organ transplant patients, cancer and leukemia patients Fungi reproduction • May have sexual and asexual reproduction • Asexual by fragmentation, budding • Spores are produced sexually (via meiosis) • 1. Fragmentation-pieces of hypha break off and grow new pieces • 2. Budding-mitosis occurs and a new individual pinches off from parent (ex. Yeast) • 3. Spores- most fungi produce spores-hypha emerges from it like seeds Advantages of spores: • 1. Have case that protects them-prevent from drying out • 2. Exist in a large number increasing survival chances (ex. Puffball release trillions of spores) • 3. small and lightweight- disperse easy by wind Plant pathology • Most plant diseases are caused by fungi. Medical importance – • 50-100 species are recognized human pathogens. • Most prefer to be free-living saprophytes; and only accidentally become pathogens. Plant pathology • To be pathogenic, they must tolerate the temperature of the host site and possess an enzymatic system that allows them to utilize animal tissues. • Increased incidence of fungal infections in recent times..

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