Microbiology of Common Skin Pathogens-Fungal

Question 1

What are the most common cutaneous and superficial mycoses?

Answer 1

• Tinea (ringworm)= Dermatophyte
• Candida
• Tinea versicolor= Malassezia furfur
• Tinea nigra

Question 2

What are the Dermatophytes?

Answer 2

• mycoses that infect the keratinized layer of hair, skin, or nails.
• isolated from soil (geophilic), animals (zoophilic), or people (anthropophilic).

Question 3

What are the 3 genera of dermatophytes? (see slide with all 3 pictures)

Answer 3

1. Microsporum
2. Trichophyton
3. Epidermophyton

Question 4

Do anthropophilic or zoophilic dermatophytes tend to induce a stronger inflammatory reaction in humans?

Answer 4

• zoophilic (also geophilic).

* followed by a rapid termination of the infection.

Question 5

What dermatophyte is the most common cause of athlete’s foot (tinea pedis)?

Answer 5

• Trichophyton rubrum

Question 6

Where is the dermatophyte Microsporum canis most commonly found?

Answer 6

• cats and dogs

* infects body in adult humans and the scalp of children.

Question 7

What are the types of Tinea (ringworm)?

Answer 7

• tinea capitis= scalp
• tines pedis= feet
• tinea manuum= hands
• tinea cruris= groin
• tinea barbae= beard, hair
• tinea corporis= body
• tinea unguium (onychomycosis)= nails

Question 8

What are the 3 subtypes of Tinea capitis?

Answer 8

1. ECTOTHRIX= arthroconidia on the outside of the hair shaft that often fluoresce. Destroys the cuticle of the hair.
2. ENDOTHRIX= arthroconidia in the hair shaft. Hair cuticle remains intact.
3. FAVUS= associated with Trichophyton schoenleinii. Crusting, scarring, and permanent hair loss. Look for FAVIC CHANDELIERS (ANTLER SHAPED HYPHAE).

Question 9

What is a kerion?

Answer 9

• severe inflammatory response to tinea capitis causing hair loss and purulent drainage.

Question 10

What is the most common cause of tinea capitits in the U.S.?

Answer 10

• Trichophyton tonsurans= ENDOthrix

Question 11

Does athletes foot increase your risk for cellulitis?

Answer 11

YES

Question 12

How do you diagnose a dermatophyte infection?

Answer 12

• septated hyphae seen in KOH (calcofluor white) preps of skin scrapings.
• some Mircrosporum fluoresce under UV light (Woods light).

Question 13

What do microconidia look like?

Answer 13

• tiny dots with spindle shaped macroconidia

* note: macro and microconidia are seen when cultured; NOT in skin scrapings.

Question 14

What is the most common nosocomial fungal pathogen?

Answer 14

• Candida albicans= forms GERM TUBES.

Question 15

What is important to know about Candida?

Answer 15

• yeast and pseudohyphae in tissue
• normal flora in the oral cavity, lower GI tract, and female genital tract.
• beginning to form resistance to fluconazole.

Question 16

What are the types of mucous membrane candidiasis infections?

Answer 16

• ORAL THRUSH= infants and immunocompromised pts; white plaques on buccal mucosa, tongue, gums, or palate.
• VAGINAL CANDIDIASIS= predisposing factors include pregnancy, DM, and antibiotic therapy; thick white discharge causing itching, discomfort, and dysuria.

Question 17

What is oncyhomycosis (chronic nail infection) of cutaneous candidiasis?

Answer 17

• resembles dermatophyte infection, which actually may initiate the infection.
• occurs on warm, moist areas of skin (diaper rash) and causes a red rash with satellite lesions that can coalesce.

Question 18

What are the predisposing factors for cutaneous candidiasis?

Answer 18

• borad spectrum ABX
• DM
• obesity

Question 19

What is a good way to differentiate cutaneous candidiasis from dermatophytes?

Answer 19

• SATELLITE LESIONS occur with candida, but not dermatophytes.

Question 20

What does Tinea versicolor (Malassezia furfur; pityriasis) look like?

Answer 20

• light hypopigmented or coppery-brown, minimally scaly papules and plaques.
• usually on trunk and back and noticed in the summer bc lesions don’t tan.
• colonized skin as yeast.
• grows best on OILY AREAS (lipophilic).

Question 21

Can Tinea versicolor (Malassezia furfur; pityriasis) act as an opportunistic fungus?

Answer 21

• YES, by colonizing catheters in neonatal ICUs or in immunocompromised individuals.

Question 22

Where is Malassezia pachydermatis commonly found?

Answer 22

• common in cats and dogs

Question 23

Does Malassezia furfur fluoresce under Wood’s light?

Answer 23

YES

*skin scraping reveal yeast and pseudohyphae (spaghetti and meatballs).

Question 24

What are some other clinical manifestations of Malassezia furfur?

Answer 24

• Pityriasis folliculitis= papules and pustules at hair follicles.
• seborrhoeic dermatitis and dandruff= flaky, white to yellowish scales at moist, oily areas of scalp, face, and ears.

Question 25

What is important to know about Tinea nigra? (not commonly found in U.S.)

Answer 25

- Hortaea werneckii - dematiaceous fungus on soil, compost, wood. - rare; mostly seen in tropics. - brown to black lesions (non-scaling) on hands and feet. - skin scrapings show brown septate hyphae and 2-celled yeast cells.

Question 26

What are white and black piedra?

Answer 26

- white (soft) or black (gritty) nodules along the hair shaft. - caused by Trichosporon species (white) or Piedraia hortae (black).

Question 27

What are the 4 subcutaneous mycoses?

Answer 27

1. Sporotrichosis 2. Phaeohyphomycosis 3. Chromoblastomycosis 4. Mycetoma

Question 28

How are the subcutaneous mycoses transmitted?

Answer 28

- via inoculation into a puncture wound, and cause a slow, chronic infection.

Question 29

What is important to know about Sporotrichosis (subcutaneous mycosis)?

Answer 29

- dimorphic fungus caused by Sporothrix schenckii. - causes open ulcers. - found in soil and on plants (rosebushes and mulches). - occupational disese of gardeners, florists, farmers...

Question 30

How does sporotrichosis spread?

Answer 30

- along lymphatics

Question 31

Can sporotrichosis affect the lungs?

Answer 31

YES if inhaled (pulmonary sporotrichosis).

Question 32

How do you diagnose sporotrichosis?

Answer 32

- biopsy of lesion= yeasts in tissue, asteroid bodies (yeast cell surrounded by rays of eosinophilic material containing antigen-antibody complexes). - culture= most reliable; grows in 2-5 days.

Question 33

What is important to know about Phaeohyphomycosis (subcutaneous mycosis)?

Answer 33

- dematiaceous fungus that forms pigmented yeast or hyphae. - inflammatory cyst forms at site of inoculation (single subcutaneous abscess). - can cause sinusitis or brain abscess.

Question 34

What is important to know about Chromoblastomycosis (subcutaneous mycosis)?

Answer 34

- well defined scaly, wart-like plaque (cauliflower lesion). | - scrapings show golden-yellow septate spherical bodies (SCLEROTIC BODIES), which divide by fission (NOT BUDDING).

Question 35

What is important to know about Mycetoma (Madura foot)?

Answer 35

- traumatic inoculation by fungus (eumycetoma) or bacteria (actinomycetoma). - chronic suppurative infection; abscess formation (pus contains microcolonies of agent). - starts as small, firm, painless nodule. - spreads from subcutaneous tissue to fascia and bone.