Dermatophytes Flashcards
fungi that infect superficial areas of body, such as hair, skin and nails
dermatophyte
Infection of keratinized tissue
dermatophytosis
Infections of the head
tinea capitis
infections of the body
tinea corporis
infections of the beard
tinea barbae
infections of the groin (jock itch)
tinea cruris
infections of the foot (athlete’s foot)
tinea pedis
infections of the nail
tinea unguium
nail infection by non-dermatophytes
onchomycosis
Dermatophyte infections are commonly referred to as “tinea” or “_______”
ringworm
why do dermatophytes generally only infect hair, skin and nails?
They use keratin as nitrogen source
What is the most common of human fungal infections
dermatophyte
What are the three ways to identify a dermatophyte infection?
- Direct physical examination
- Lab examination of specimen (skin scraping, hair, toenail)
- Culture
What are 4 Direct Physical Exams
- Wood’s lamp (UV)
- Potassium hydroxide (KOH)
- Calcoflour white - fungi fluoresce
- Exam of hair for ectothrix or endothrix invasion
In Wood’s Lamp Exam:
- Microsporum in hair fluoresces ________
- Skin with tine versicolor fluoresces ________
- Trichophyton fluoresces _________
- yellow-green
- yellow
- does NOT fluoresce
Culture:
- what medium and what does it do?
Primary isolation medium + cyclohexamide to kill skin contaminants (CSAB) (Mycosel or Mycobiotic Agar)
Culture:
- incubation time?
2-4 weeks (recommended 30 days)
Most identifications are by ______ ______
microscopic morphology (microconidia/macroconidia)
Trichophyton infects what?
hair, skin, and nail (especially feet and nails)
Trichophyton:
- Microconidia vs Macroconidia
Microconidia: important for identification
Macroconidia: rarely helpful
Trichophyton:
- other tests available?
- does it fluoresce with Wood’s lamp?
- Biochemical tests available
- does NOT fluoresce
Second most common cause of dermatophytosis
Trichophyton rubrum
Trichophyton rubrum:
- Reverse
most are cherry red (>3 weeks)
Trichophyton rubrum:
- What do they look like?
tiny teardrop microconidia; “birds on a wire”
Trichophyton rubrum
- Urease reaction
negative
Trichophyton rubrum
- Hair perforation reaction
Negative
Trichophyton mentagrophytes:
- 2 types of colonies
- downy: from feet
- granular: infection spread from animals
Trichophyton mentagrophytes:
- reverse
May be red/brown (medium dependent)
Trichophyton mentagrophytes:
- microscopic mold appearance
- hyphae may be spiral shaped
- tear-shaped microconidia often in grape like clusters
- macroconidia cigar shaped
Trichophyton mentagrophytes:
- urease reaction
Positive
Trichophyton mentagrophytes:
- hair perforation test reaction
Positive
1 cause of tinea capitis in US (especially children) and wrestlers, hence “tinea gladiotorium)
Trichophyton tonsurans
Trichophyton tonsurans:
- Colonies
Buff/brown (May be rust colored on reverse), wrinkled or cratered
Trichophyton tonsurans:
- Microconidia appearance
Elongated balloons or stretched teardrops
Trichophyton tonsurans:
- grows poorly on most media, growth enhanced by __________
Thiamin (T4 agar vs T1 agar)
Trichophyton tonsurans:
- any hair infection?
Endothrix infection (fungus inside hair shaft), hair brakes at scalp ( “Black dot”)
Trichophyton verrucosum:
- causes tinea ______
Capitus (another cause of “black dot”)
Trichophyton verrucosum:
- what type of people are at risk
Cattle/dairy workers
Trichophyton verrucosum:
- lesions often misdiagnosed as what type of infection
Staph infection
Trichophyton verrucosum:
- microscopic appearance
“antler hyphae” and chlamdoconidia “armadillo/rat tails”
Trichophyton verrucosum:
- Will it grow at 37°C
- growth is enhanced at 37°C
Trichophyton schoenleinii:
- what infection does it cause
- causes favus (tinea capitus) - scarring and permanent hair loss (yellow, thickened, cup shaped crusts)
Trichophyton schoenleinii:
- colony appearance
Gray and waxy
Trichophyton schoenleinii:
- microscopic appearance
- conidia are rare, club/antler shaped hyphae and “favic chandeliers”
- branching hyphae seen within hairs (tunnels)
Trichophyton schoenleinii:
- common in what countries
Appalachia and Scandinavian countries
