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MSS > Microbiology of Common Skin Pathogens-Fungal > Flashcards

Microbiology of Common Skin Pathogens-Fungal Flashcards

1
Q

What are the most common cutaneous and superficial mycoses?

A
  • Tinea (ringworm)= Dermatophyte
  • Candida
  • Tinea versicolor= Malassezia furfur
  • Tinea nigra
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2
Q

What are the Dermatophytes?

A
  • mycoses that infect the keratinized layer of hair, skin, or nails.
  • isolated from soil (geophilic), animals (zoophilic), or people (anthropophilic).
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3
Q

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

A
  1. Microsporum
  2. Trichophyton
  3. Epidermophyton
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4
Q

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

A
  • zoophilic (also geophilic).

* followed by a rapid termination of the infection.

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5
Q

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

A
  • Trichophyton rubrum
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6
Q

Where is the dermatophyte Microsporum canis most commonly found?

A
  • cats and dogs

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

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7
Q

What are the types of Tinea (ringworm)?

A
  • tinea capitis= scalp
  • tines pedis= feet
  • tinea manuum= hands
  • tinea cruris= groin
  • tinea barbae= beard, hair
  • tinea corporis= body
  • tinea unguium (onychomycosis)= nails
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8
Q

What are the 3 subtypes of Tinea capitis?

A
  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).
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9
Q

What is a kerion?

A
  • severe inflammatory response to tinea capitis causing hair loss and purulent drainage.
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10
Q

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

A
  • Trichophyton tonsurans= ENDOthrix
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11
Q

Does athletes foot increase your risk for cellulitis?

A

YES

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12
Q

How do you diagnose a dermatophyte infection?

A
  • septated hyphae seen in KOH (calcofluor white) preps of skin scrapings.
  • some Mircrosporum fluoresce under UV light (Woods light).
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13
Q

What do microconidia look like?

A
  • tiny dots with spindle shaped macroconidia

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

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14
Q

What is the most common nosocomial fungal pathogen?

A
  • Candida albicans= forms GERM TUBES.
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15
Q

What is important to know about Candida?

A
  • yeast and pseudohyphae in tissue
  • normal flora in the oral cavity, lower GI tract, and female genital tract.
  • beginning to form resistance to fluconazole.
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16
Q

What are the types of mucous membrane candidiasis infections?

A
  • 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.
17
Q

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

A
  • 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.
18
Q

What are the predisposing factors for cutaneous candidiasis?

A
  • borad spectrum ABX
  • DM
  • obesity
19
Q

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

A
  • SATELLITE LESIONS occur with candida, but not dermatophytes.
20
Q

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

A
  • 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).
21
Q

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

A
  • YES, by colonizing catheters in neonatal ICUs or in immunocompromised individuals.
22
Q

Where is Malassezia pachydermatis commonly found?

A
  • common in cats and dogs
23
Q

Does Malassezia furfur fluoresce under Wood’s light?

A

YES

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

24
Q

What are some other clinical manifestations of Malassezia furfur?

A
  • 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.
25
Q

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

A
  • 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.
26
Q

What are white and black piedra?

A
  • white (soft) or black (gritty) nodules along the hair shaft.
  • caused by Trichosporon species (white) or Piedraia hortae (black).
27
Q

What are the 4 subcutaneous mycoses?

A
  1. Sporotrichosis
  2. Phaeohyphomycosis
  3. Chromoblastomycosis
  4. Mycetoma
28
Q

How are the subcutaneous mycoses transmitted?

A
  • via inoculation into a puncture wound, and cause a slow, chronic infection.
29
Q

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

A
  • dimorphic fungus caused by Sporothrix schenckii.
  • causes open ulcers.
  • found in soil and on plants (rosebushes and mulches).
  • occupational disese of gardeners, florists, farmers…
30
Q

How does sporotrichosis spread?

A
  • along lymphatics
31
Q

Can sporotrichosis affect the lungs?

A

YES if inhaled (pulmonary sporotrichosis).

32
Q

How do you diagnose sporotrichosis?

A
  • 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.
33
Q

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

A
  • dematiaceous fungus that forms pigmented yeast or hyphae.
  • inflammatory cyst forms at site of inoculation (single subcutaneous abscess).
  • can cause sinusitis or brain abscess.
34
Q

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

A
  • well defined scaly, wart-like plaque (cauliflower lesion).

- scrapings show golden-yellow septate spherical bodies (SCLEROTIC BODIES), which divide by fission (NOT BUDDING).

35
Q

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

A
  • 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.

MSS (9 decks)

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