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Mycology

Mycology. General Properties of fungi: Fungi are a diverse group of saprophytic and parasitic eukaryotic organisms that varies in complexity and size, ranging from the single-cell microscopic yeasts to multicellular molds, macroscopic puffballs, and mushrooms.

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Mycology

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  1. Mycology General Properties of fungi: Fungi are a diverse group of saprophytic and parasitic eukaryotic organisms that varies in complexity and size, ranging from the single-cell microscopic yeasts to multicellular molds, macroscopic puffballs, and mushrooms. Fungi can be distinguished from other infectious organisms by: 1- They are Eukaryotes (that is, they have a membrane-enclosed nucleus, and other membrane bounded organelles). 2- Cell wall and membrane components: • Fungal cell wall are composed largely of Chitin, a polymer of N-acetylglucosamine, rather than peptidoglycan. • The fungal membrane contains ergosterol, rather than the Cholesterol found in mammalian membranes. Dr. Rania Alhady

  2. Mycology 3-All fungi are Heterotrophes, Chemotrophic, and non-phototrophic organisms. Fungi secrete degradative enzymes ( cellulases, proteases, nucleases) into their immediate environment. 4- Fungi are Facultative anaerobic or obligatory aerobic organisms. 5- Most fungi are Acidophilic organisms. 6- Fungi reproduce and spread through the environment by Spore formation which may be sexual or asexual. Dr. Rania Alhady

  3. Fungi Morphology Fungi Morphology: Fungi exist into two main forms yeasts or hyphae (Moulds). Some fungi may occur in both the yeast and mycelial forms. These are called dimorphic fungi. (A)Filamentous fungi:They grow as hyphae and reproduce by asexual spores (conidia), which may be unicellular called “microconidia” or multicellular and are called “macroconidia”. (B) Yeasts:areUnicellular non-branched, oval or rounded cells, measuring 3-15 µm in diameter. • Yeasts reproduce asexually by budding (blastospore, and chlamydospores). • They may form chains of elongated filamentous cells called “pseudohyphae”. Dr. Rania Alhady

  4. Fungi Morphology Dr. Rania Alhady

  5. Fungi Morphology (C) Dimorphic fungi: These fungi are changing their morphology from mould to yeast phase, or from yeast to mould depending on the growth conditions (has 2 morphologies & 2 diagnostic temperatures). 1. Yeast: (parasiticor pathogenic form): This is the form usually seen in tissue, in exudates (body temperature) , or if cultured in an incubator at 37ºC. They grow as yeasts. 2. Mycelium: (saprophytic or mold form): This is the form observed in nature (room temperature) or when cultured at 25ºC. They grow as filaments. Dr. Rania Alhady

  6. Fungi Morphology Dr. Rania Alhady

  7. Fungal Diseases Fungal Diseases: • Fungal diseases can be classified into the following groups: • 1- Hypersensitivity: an allergic reaction to molds and spores. Indoor air pollution. • Example : hypersensitivity pneumonitis, rhinitis, bronchial Asthma, and alveolitis. • 2- Mycotoxicoses: poisoning of man and animals due to accidental ingestion of food contaminated by toxic compounds produced by fungi. • Examples of toxic metabolites: • A-Ergot alkaloids, produced by Clavicepspurpureathat infects rye and other grains. ( disease : Ergotism) • B-Aflatoxins, produced by Aspergillusflavusthat infects Rice, corn, peanuts, and soybeans. ( disease: aflatoxicosis) • 3- Mycetismus: the ingestion of Amanitins (a toxin produced by mushroom species called Amanita verna. ( mushroom poisoning). • 4- Infection (Mycoses): Dr. Rania Alhady

  8. Fungal Diseases Infection (Mycoses): • Fungi infection (Mycosis) can be divided into the following: • 1- Superficial(Hair, skin, nail, cornea) mycosis. • 2- Subcutaneousmycosis. • 3- True systemic (endemic) mycosis. • 4- Opportunisticmycosis. • SUPERFICIAL MYCOSES: • The superficial mycoses are usually limited to the outermost layers of the skin, hair, and nails, and do not invade living tissues. • Types: • 1- Pityriasisversicolor 2- Dermatophytosis. • 3- Tineanigra. 4- Black piedra. 5- White piedra. Dr. Rania Alhady

  9. Fungal Diseases • PityriasisVersicolor: It is a superficial chronic infection of stratum corneum.This fungal infection is caused by Malassezia furfur, a lipophilic yeast like organism. • TineaNigra: Superficial chronic infection of stratum corneum Etiology: Hortae(Exophiala) werneckii(producing melanin). Black Piedra: It is a superficial fungal infection of the scalp hair. Etiology: Piedraiahortae White Piedra: Fungal infection of facial, axillary or genital hair . Etiology: Trichosporonbeigelii(yeast) Dr. Rania Alhady

  10. Fungal Diseases Pityriasisversicolor, Tineanigra, black and white Piedra: Dr. Rania Alhady

  11. Fungal Diagnosis Laboratory Diagnosis of Fungal Infections: (1) Specimens: According to the site of infection as, skin scales, hairs, nails, respiratory secretions, blood, … (2) Direct Detection: A- Direct microscopy of unstained preparations (mounting method): Examination of unstained preparations to demonstrate hyphae, spores or yeast cells. Skin scraping, nails or hairs are mounted with 10-20% KOH to digest the keratin layer so that hyphae and spores can be seen. B- Direct microscopy of stained preparations: Different stains are used, e.g. India ink, Periodic Acid Schiff (PAS), silver stain and Lactophenol cotton blue stain (specific fungal stain). Dr. Rania Alhady

  12. Fungal Diagnosis (3) Culture: Sabouraud`s dextrose agar (SDA): the standard media for most fungi. Chloramphenicol added to inhibit bacterial growth & cycloheximide added to inhibit saprophytic fungi. Incubation temperature is 22°C. If systemic mycosis is suspected, Enriched media is used and incubated at 37°C. (4) Serodiagnosis: Detection of specific antibody help in diagnosis of systemic mycosis. (4) Cutaneous delayed type hypersensitivity test: Example: histoplasmin skin test and blastomycin skin test. For identification of systemic mycosis. Dr. Rania Alhady

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