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Introduction to Mycology

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Presentation on theme: "Introduction to Mycology"— Presentation transcript:

1 Introduction to Mycology

2 General Properties of fungi
Fungi are a diverse group of saprophytic and parasitic eukaryotic organisms They varies in complexity and size ranging from the single-cell microscopic yeasts to multicellular molds

3 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

4 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

5 3- All fungi are Heterotroph, and Chemotrophic 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

6 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 Hyphae are multicellular filamentous structures, constituted by tubular cells with cell walls


8 Hyphae of Penicillium


10 Yeast Yeasts are Unicellular non-branched, oval or rounded cells
measuring µm in diameter Yeast of the species Saccharomyces cerevisiae

11 Yeasts reproduce asexually by budding (Blastospore, and Chlamydospore)
Chlamydospores of the yeast Candida albicans

12 Dimorphic fungi These fungi are changing their morphology from mould to yeast phase, or from yeast to mould depending on the growth conditions 1. Yeast (parasitic or pathogenic form) This is the form usually seen in tissue, in exudates, or if cultured in an incubator at 37ºC 2. Mycelium ( saprophytic or mold form) The form observed in nature or when cultured at 25ºC


14 Fungal Diseases Fungal diseases can be classified into the following groups 1-Hypersensitivity (allergy) It is an allergic reaction to molds and spores ( Indoor air pollution) 2-Mycotoxicoses Poisoning of man and animals due to accidental ingestion of food contaminated by toxic compounds produced by fungi Examples A- Ergotism: caused by Claviceps purpurea; (Ergot alkaloids) B- Aflatoxicosis: caused by Aspergillus flavus (Aflatoxins)

15 Ergotism Ergotism

16 3-Mycetismus 4-Infection (Mycosis)
Due to ingestion of Amanitins (a toxin produced by a specific type of mushroom ; Amanita verna ) 4-Infection (Mycosis) A-Superficial (Hair, skin, nail, cornea) mycosis B-Subcutaneous mycosis C-True systemic (endemic) mycosis D-Opportunistic mycosis

17 SUPERFICIAL MYCOSIS The superficial mycoses are usually limited to the outermost layers of the skin, hair, and nails, and do not invade living tissues Most common Types: 1- Dermatophytosis 2- Pityriasis versicolor

18 Dermatophytosis (Tinea or Ringworm)
It is a type of superficial skin infection of cutaneous layer (mainly epidermis) Causes: Epidermophyton Microsporum Trichophyton

19 Pityriasis Versicolor
It is a superficial chronic infection of stratum corneum. This fungal infection is caused by Malassezia furfur

20 Other superficial infection of skin
Tinea Nigra, Black Piedra, and White Piedra are caused by Exophiala werneckii, Piedraia hortae, and Trichosporon species respectively Tinea Nigra Black Piedra White Piedra

21 1-Tinea Nigra 2-Black Piedra 3-White Piedra Exophiala werneckii
Infection of Stratum corneum 2-Black Piedra Piedraia hortae Infections of scalp hair 3-White Piedra Trichosporon beigelii Fungal infection of facial, axillary or genital hair

22 Types of superficial Mycosis

23 Subcutaneous Mycosis Sporotrichosis
Caused by Sporothrix schenkii At 25°C: Septate hyphae, rosette-like clusters of conidia at the tips of the hyphae At 35 C: Yeast

24 Systemic Mycosis Respiratory system infection Causes
Chronic granulomatous pneumonia Causes Histoplasma capsulatum (dimorphic fungi) Coccidioides immitis (dimorphic fungi)

25 Opportunistic mycosis
Candidiasis Candida albicans infection Example: 1-Oral Candidiasis 2-Vaginal Candidiasis

26 Laboratory Diagnosis of Fungal Infections
(1) Specimens According to the site of infection Skin scales Hairs Nails Respiratory secretions Blood

27 (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

28 B- Direct microscopy of stained preparations
Different stains are used India ink Periodic acid-Schiff stain (PAS) Silver stain Lactophenol cotton blue stain (specific fungal stain)

29 Incubation temperature is 22°C
(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

30 (5) Cutaneous delayed type hypersensitivity test
(4) Serodiagnosis Detection of specific antibody help in diagnosis of systemic mycosis (5) Cutaneous delayed type hypersensitivity test Example Histoplasmin skin test Histoplasma capsulatum Blastomycin skin test Blastomyces dermatitidis For identification of systemic mycosis

31 Dermatophyte morphology

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