Introduction to Mycology

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

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

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

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

Hyphae of Penicillium

Yeast Yeasts are Unicellular non-branched, oval or rounded cells measuring 3- 15 µm in diameter Yeast of the species Saccharomyces cerevisiae

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

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

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)

Ergotism Ergotism

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

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

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

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

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

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

Types of superficial Mycosis

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

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

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

Laboratory Diagnosis of Fungal Infections (1) Specimens According to the site of infection 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 India ink Periodic acid-Schiff stain (PAS) Silver stain Lactophenol cotton blue stain (specific fungal stain)

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

(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

Dermatophyte morphology