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. 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 utilitize animal tissues. Increased incidence of fungal infections in recent times. Infection to the human body Fungus can cause allergic reactions- respiratory problems. Growth of a fungus on or in the body • Superficial mycoses-Tinea pedis-Athlete’s foot • Subcutaneous mycoses-sporotrochosis-caused by skin puncture from thorns or vegetation contaminated with fungi • Systemic mycosis-Coccidioides immitis-desert fever The Immunosuppressed Patient: AIDS Drugs - immunosuppressant drugs used in organ transplant patients, cancer and leukemia patients Importance of Medical Mycology During the time period between 1941 - 1973, the number of reported deaths in the U.S. due to scarlet fever, typhoid, whooping cough, diphtheria, dysentery and malaria decreased from 10,165 cases to 107; but reported deaths due to mycoses during the same time period, increased from 324 to 530. Importance of Medical Mycology Increased mobility - We can travel to a geographical area where a fungus exists as part of the commensal flora of the local population, or is endemic to the area. ..

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