Mycology Flashcards
(95 cards)
Describe the defining characteristics of Malassezia furfur.
It is a lipophilic yeast that has short hyphae. Normal part of skin flora.
“Spaghetti and meatballs” appearance in skin scrapings.
What superficial mycoses are associated with Malassezia furfur? What distinguishes these mycoses?
Pityriasis versicolor (tinea versicolor) - infection of stratum corneum, may be hypo- or hyperpigmented itchy macules; fluoresce under Wood’s lamp.
Seborrheic dermatitis - squamous disorder of sebum rich areas of scalp; dandruff
Follicular pityriasis - infected follicles show yeast at their openings
What stains or solutions are used to identify Malassezia furfur?
10% KOH, glycerol and Parker’s stain
20% KOH
What organisms cause the superficial mycoses?
Malassezia furfur
Trichosporon beigelii
Piedraia hortae
Hortae werneckii
Describe the characteristics of Trichosporon beigelii. What conditions are associated with it?
Mycelial and yeast like morphologies, normal flora of mouth and skin. Has hyaline, septate hyphae and oval arthroconidia.
It causes white piedra
Briefly describe Piedraia hortae. What conditions does it cause?
Filamentous mold with dark septate hyphae.
Causes black piedra.
Describe Hortae werneckii. What does it cause?
Filamentous mold with brown septate hyphae or dark brown budding cells in KOH.
Causes tinea nigra - hyperpigmented macula on palms and soles.
What is a dermatophytosis?
Dermatophytoses or cutaneous mycoses are infections of the skin where the stratum corneum is colonized. The causative organisms use keratinase to digest keratin and use it as nutrient.
They induce pathological changes and may involve cellular immune responses.
Cause ringworm lesions.
Which organisms cause the dermatophytoses?
Microsporum spp.
Trichophyton
Epidermophyton
Describe the Microsporum genus.
Spindle shaped, thick walled and rough macroconidia.
What defines a fungal infection as a dermatomycoses?
Limited to the outer keratinized layer of skin and hair, they do not elicit a cellular immune response and are not pathologic. Cause only cosmetic problems.
Describe the Epidermophyton genus.
Smooth, thin walled club shaped macroconidia
Describe the Trychophyton genus
They have thin walled, smooth, pencil shaped macroconidia.
What are the different manifestations of tinea capitis? What is the causative organism of each?
Ectothrix - development of arthroconidia outside hair shaft; fluoresces green; Microsporum canis and gypseum, Trichophyton verrucosum
Endothrix - arthroconidia within hair shaft; no fluorescence; Trichophyton tonsurans and violaceum
Favus - acute infection of hair follicle; produces crust and hair loss, green flourescence; Trichophyton schoenleinii
Whatbare the etiologic agents of tinea corporis?
Epidermophyton floccosum
Trichophyton rubrum and tonsurans
Microsporum canis and gypseum
What are the etiologic agents of onychomycosis?
Trichophyton rubrum
Trichophyton interdigitale
What are the etiologic agents of tinea cruris?
Trichophyton rubrum
Trichophyton interdigitale
Epidermophyton floccosum
What is a subcutaneous mycosis? What is the etiologic agent?
A subcutaneous mycosis is a fungal infection of the deeper layers of the dermis, the subcutaneous tissue, and deeper tissues like bone. They are followed by chronic and insidious growth. Saprophytes found in soil or decaying vegetation are the etiologic agents.
How does a subcutaneous mycosis generally start?
Usually begins with trauma. They are mycoses of implantation.
What is the causative agent of sporotrichosis? What are the characteristics of this organism?
Sporothrix schenkii. It is a thermally dimorphic fungus.
Sporotrichosis is known as the rose gardner’s disease
What determines the pathogenicity of sporotrichosis?
Dimorphism and thermotolerance.
Glycoprotein on cell wall mediates attachment.
Asteroid body deposits protect yeast from immune attack.
Describe the morphology of Sporothrix mold and yeast
Sporothrix mold has branching septate hyphae and conidiophores. Described as a flower like arrangement. (Floret or daisy cluster).
The yeast form appears as short round oval or cigar shaped.
What characterizes chromoblastomycosis/chromomycosis?
Nodular and verrucous lesions; thick walled pigmented sclerotic bodies in tissues
What determines the pathogenicity of chromomycosis?
Dimorphism.
Melanin.
Enzymes.
Platelet activating factor .