Microbiology of Common Skin Pathogens-Fungal Flashcards Preview

MSS > Microbiology of Common Skin Pathogens-Fungal > Flashcards

Flashcards in Microbiology of Common Skin Pathogens-Fungal Deck (35):

What are the most common cutaneous and superficial mycoses?

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


What are the Dermatophytes?

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


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

1. Microsporum
2. Trichophyton
3. Epidermophyton


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

- zoophilic (also geophilic).
*followed by a rapid termination of the infection.


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

- Trichophyton rubrum


Where is the dermatophyte Microsporum canis most commonly found?

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


What are the types of Tinea (ringworm)?

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


What are the 3 subtypes of Tinea capitis?

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).


What is a kerion?

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


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

- Trichophyton tonsurans= ENDOthrix


Does athletes foot increase your risk for cellulitis?



How do you diagnose a dermatophyte infection?

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


What do microconidia look like?

- tiny dots with spindle shaped macroconidia
*note: macro and microconidia are seen when cultured; NOT in skin scrapings.


What is the most common nosocomial fungal pathogen?

- Candida albicans= forms GERM TUBES.


What is important to know about Candida?

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


What are the types of mucous membrane candidiasis infections?

- 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.


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

- 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.


What are the predisposing factors for cutaneous candidiasis?

- borad spectrum ABX
- DM
- obesity


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

- SATELLITE LESIONS occur with candida, but not dermatophytes.


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

- 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).


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

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


Where is Malassezia pachydermatis commonly found?

- common in cats and dogs


Does Malassezia furfur fluoresce under Wood's light?

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


What are some other clinical manifestations of Malassezia furfur?

- 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.


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

- 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.


What are white and black piedra?

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


What are the 4 subcutaneous mycoses?

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


How are the subcutaneous mycoses transmitted?

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


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

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


How does sporotrichosis spread?

- along lymphatics


Can sporotrichosis affect the lungs?

YES if inhaled (pulmonary sporotrichosis).


How do you diagnose sporotrichosis?

- 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.


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

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


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

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


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

- 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.