Lect 24 Flashcards
What are Dermatophytes
- pathogenic fungi
Dermatophytes require what for growth
- keratin
- hair, nails, skin
- *do not infect mucosal surfaces
Dermatophytes secrete what enzyme that allows for inhabiting keratinized regions of the body
keratinase
What are the three important genera of Dermatophytes? Which can form sexual spores?
- Epidermophyton
- Microsporum**
-
Trichophyton**
- ** sexual spores
What is the infective stage of disease in Dermatophytes
-
Arthroconidium
- can be visulaized in 1-% KOH wet mount
How are Dermatophytes diagnosed
- Hyphae and Arthoconidia can be visualized in dead keratinized tissue
- 10% KOH
- dermatophyte test medium
- sabouraud agar
what is the crude antigen of Dermatophytes (not seen on any other fungus)
Trichophytin: Galactomannan peptide
Trichophytin will create what two immune responses
- CHO component: immediate response
- peptide component: delayed response
the dermatophyte test medium takes advantage of what property of dermatophytes
- dermatophytes utilize nitrogenous compounds preferentially over carbohydrates
- change pH (alkaline) - red color change
dermatophytes can be classified into what 3 groups based on transmission
-
Zoophilic
- animal pathogens that may be transmitted to people
-
Antrophophilic
- human transmission
-
Geophilic
- transmitted through soil to people
- usually invade non-viable keratinized tissue
What types of spores can dermatophytes produce
- Arthrospores: person to person transmission; survive in environment
- microconidia: asexual
- macroconidia: asexual; usually multicellular
- sexual spores
typical clinical manifestation of dermatophyte infection
- lesions are inflammed at edges with a central clearing zone
- hair loss with itching, but not debilitating
predisposing factors to developing dermatophyte infection
- nail trauma
- HIV
- DM
- immunosuppressive meds
What is an allergic dermal reaction to fungal antigens occuring in areas devoid of organisms
“Id reaction”: Dermatophytid
how to prevent dermatophyte infections
- good personal hygiene
- keep skin dry
- regular housecleaning
- use chlorine bleach and detergents
What are the most common Trichophyton species
- T. tonsurans
- T. rubrum
- T. mentagrophytes
features of Trichophyton species
- all make pencil-shaped macroconidia with thin walls
- not often fluorescent
- produce
- hyphae
- microconidia
- macroconidia
What is the most common cause of tinea capitis
Microsporum canis
features of Microsporum species
- exhibit fluorescence under woods’s lamp
- produce
- hyphae
- microconidia
- macroconidia
- large, spindle shaped
- multicellular
- thick walled
Tinea capitis infects what
- “ringworm of the scalp”
- infects
- endothrix: internal part of hair follcile
- extothrix: external part of hair follicle
- scalp
In a tinea capitis infection, infected hair can break off leadint to
alopecia
- see black dots of hair loss
What does tinea pedis present as
- athletes foot
- itching, peeling and cracking of the skin
- toe webs and soles
Predisposing factors for Tinea corporis and Tinea cruris (jock itch)
- Diabetes
- obesity
- excessive perspiration
how is Tinea corporis and Tinea cruris (jock itch) transmitted
- direct and indirect contact objects
- towels, clothing, bed linen
What is Tinea Unguium
- onychomycosis: ringworm of the nail
Tinea Unguium usually has co-infection with
candida species
What is another name for Malassezia furfur
Tinea versicolor
features of Malassezia furfur
- short, unbranched hyphae and somewhat spherical cells
- “spaghetti and meatballs” arrangement
- yeast-like colonies
Malassezia furfur has what growth factor that requires fat to grow
- lipophilic growth factor
clinical presentation
- lesions occurs as a macular patch of depigmented or hyperpigmented skin that may enlarge, can lead to dandruff
Malassezia furfur
how is Malassezia furfur diagnosed
microscopic exam in skin scrapings: KOH
What is another name for Hortaea werneckii
tinea nigra
unique features of Hortaea werneckii
- dimorphic species
- can grow as yeast or mold
- can grow in saturated salt solutions
Hortaea werneckii produces what that creates a brownish lesion
melanin
how is Hortaea werneckii identified
KOH and microscopy
