Dermatophytes Flashcards
Fungus that infects the skin, hair, or nails (due to presence of keratin) in humans or animals
Dermatophyte
Dermatophytosis of the head
Tinea capitus
Dermatophytosis of the body
Tinea corporis
Dermatophytosis of beards
Tinea barbae
Dermatophytosis of the groin (aka “jock itch”)
Tinea cruris
Dermatophytosis of the feet (athlete’s foot)
Tinea pedis
Dermatophytosis of the nail
Tinea unguium
Nail infection caused by non-dermatophytes
Onchomycosis
Dermatophytosis
Aka ringworm
Why do dermatophytes generally only infect hair, skin, and nails?
They use keratin as their nitrogen source (invasion of the deeper tissues is very rare)
List the various ways to detect dermatophyte infections
- Direct physical examination (Wood’s lamp - UV)
- Lab examination of specimen (skin scraping, hair, toenail, etc.)
- Cultures
What are some lab examination methods?
- KOH
- Calcufluor white (fungi fluoresce)
- Ectothrix vs. endothrix invasion (in vivo)
- Hair perfusion test (in vitro)
Describe the culture method used for dermatophytes
- Primary isolation medium + cyclohexamide to kill skin contaminants (Mycosel or mycobiotic agar)
- Incubate 2-4 weeks (recommended 30 days)
- Most have fluffy white growth
Trichophyton rubrum
- Colony formation
- White and fluffy or granular
- Reverse is cherry red (>3 weeks)
VERY DISTINCT!!!!!
Trichophyton rubrum
- Microscopic formation
- Tiny teardrop microcondria (“birds on a wire”)
Trichophyton mentagrophytes
- Colony formation (2 types)
- Downy → specimen from feet
- Granular → infections spread form animals
Trichophyton mentagrophytes
- Microscopic formation
- Spiral hyphae
- Tear-shaped microconidia often in grape-like clusters
- Macroconidia are cigar-shaped
What two microscopic forms do you need to see in order to identify Trichophyton mentagrophytes?
- Macroconidia and spiral hyphae OR
- Macroconidia and tear-shaped microconidia in grape-like clusters
Trichophyton tonsurans
- Colony formation
- Buff/brown (may be rust colored on reverse), wrinkled, or cratered
- Grows poorly on most media → enhanced by thiamin (T4 agar vs. T1 agar)
Trichophyton tonsurans
- Microscopic formation
Elongated balloons OR stretched teardrops
Trichophyton verrucosum
- Colony formation
Enhanced growth @ 37°C
Trichophyton verrucosum
- Microscopic formation
- “Antler” hyphae
- Chlamydoconidia “armadillo/rat tails”
Trichophyton schoenleinii
- Colony formation
Gray and white
Trichophyton schoenleinii
- Microscopic formation
- “Club/antler-shaped” hyphae and “favic chandeliers”
- CONIDIA ARE RARE!
Epidermophyton floccosum
- Colony formation
Tan to yellowish to khaki
Epidermophyton floccosum
- Microscopic formation
Macroconidia are smooth, thin-walled, club-shaped (“beavers tail”), 2-4 cells
- NO MICROCONIDIA!
Microsporum canis
- Colony formation
- Fluffy or granular
- Reverse is bright yellow (w/ continued growth)
Microsporum canis
- Microscopic formation
- Macroconidia have thick, rough walls consisting of 3-15 cells and having a curved tip
Microsporum gypseum
- Colony formation
- Powdery, buff/cinnamon colored
- Reverse is yellow/orange/brown
Microsporum gypseum
- Microscopic formation
Macroconidia are ellipsoidal w/ rounded blunt ends, thin cell wall, 2-7 cells
Microsporum audouini
- Colony formation
Cottony white, slow growing
Microsporum audouini
- Microscopic formation
Terminal chlamydoconidia and comblike (pectinate) hyphae
How do you differentiate T. rubrum from T. mentagrophytes using the hair perforation testing?
- T. rubrum → hair perforation NEGATIVE
- T. mentagrophytes → hair perforation POSITIVE
Microsporum genus
- Amt of macroconidia vs. microconidia
Many macroconidia/few microconidia
Trichophyton genus
- Amt of macroconidia vs. microconidia
Few macroconidia/many microconidia
Epidermophyton genus
- Amt of macroconidia vs. microconidia
ONLY macroconidia
Which dermatophyte is the #1 cause of dermatophyte infections?
Trichophyton tonsurans
Which dermatophyte is the #2 of dermatophyte infections?
Trichophyton rubrum
Most common cause of favus (tinea capitus)
Trichophyton schoenleinii
Most common cause of “tinea gladatorium”
Trichophyton tonsurans
Most common cause of cattle farmer dermatophyte infections
Trichophyton verrucosum
Most common cause of dog/cat dermatophyte infections
Microsporum canis
Most common cause of tinea versicolor
Malassezia furfur
Most common soil fungus
Microsporum gypseum
Which dermatophyte does NOT fluoresce w/ a Wood’s lamp?
Trichophyton species
What is the most likely infective area for Trichophyton species?
Hair, skin, nails
What is the most likely infective area for Epidermophyton species?
Skin and nails
What is the most likely infective area for Microsporum species?
Skin and hair
Which dermatophyte is urease NEGATIVE?
Trichophyton rubrum
Which dermatophyte is urease POSITIVE?
Trichophyton mentagrophytes
Which dermatophyte fluoresces yellow-green w/ a Wood lamp?
Microsporum canis
Which dermatophyte causes an endothrix infection in the hair?
Trichophyton tonsurans
Which dermatophyte causes an ectothrix infection in the hair?
Microsporum canis
This infection is living (usually forming a spore sheath) on the surface of hair, as well as growing w/in the hair shaft
Ectothrix
This infection is growing w/in the hair shaft w/o a conspicuous external sheath of spores
Endothrix
- Hair breaks at scalp (“Black Dot”)
Which dermatophytosis is another cause of “black dot”?
Tinea capitus
