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