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Medical microbiology > Superficial Mycology > Flashcards

Superficial Mycology Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Considered as cosmetic infections where no pathologic changes are observed or living tissue is invaded or cellular host response to the fungi (Non-irritating/ asymptomatic infection)

A

Superficial mycoses

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2
Q

Two varieties of superficial mycoses

A

→ White: Pityriasis Versicolor, White Piedra
→ Black: Tinea Nigra, Black Piedra

*piedra: hair

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3
Q

Organism which causes tinea nigra

A

Exophiala werneckii

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4
Q

Organism which causes WHITE piedra

A

Trichosporon beigelii

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5
Q

Organism which causes black piedra

A

Piedraia hortae

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6
Q

Also known as Pityriasis versicolor and “An-an”

A

Tinea versicolor

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7
Q

species under genus Malasezzia which is not lipophilic

A

M. pachydermatis

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8
Q

most common isolates under genus Malasezzia

A

M globosa and restricta

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9
Q

other diseases caused by Genus Malassezia

A

dandruff (restricta)
Seborrheic dermatitis (restricta and sympodialis)
folliculitis
septicemia

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10
Q

clinical features of tinea versicolor

A

FLAT macular and demarcated lesions (with thin chalky branny scales)

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11
Q

T or F: Pigmentation of tinea versicolor lesions depend on patient’s skin color

A

true

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12
Q

What makes oily body parts (FANTS) or sebum harbor tinea versicolor pathogens?

A

waxy esters, fatty acids, triglycerides

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13
Q

Tinea versicolor should be differentially diagnosed from

A 
tinea alba (does not affect extremities usually)
vitiligo
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14
Q

color of tinea versicolor lesions under woodlamp

A

pale green

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15
Q

specimen used for microscopic examination of tinea versicolor

A

skin scrapings

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16
Q

smear used for diagnosing skin scrapings of tinea versicolor

A

KOH with Parker ink

*only edges of the fungi are seen with KOH only

17
Q

direct microscopic examination of tinea versicolor under KOH and PAS shows

A

spaghetti (blastospores) and meatballs (angular hyphal elements) appearance

*pathognomonic

18
Q

media used for culturing tinea versicolor

A

PDA with fatty acids

*circular convex creamy colonies

19
Q

it is a slow-growing saprophytic dematiaceous fungi found in soil, compost, humus and wood

A

exophiala werneckii

20
Q

tinea nigra is most commonly found where

A

palms

21
Q

clinical manifestation of tinea nigra

A

non-scaling and non-inflammatory well-demarcated gray to brown-black macular lesions

22
Q

tinea nigra must be differentially diagnosed from

A

chemical burns

skin cell carcinoma

23
Q

seen under light microscope for tinea nigra

A

Pigmented brown to dark olivaceous septate hyphal elements

Budding 2-cell yeast with melanized cell walls

24
Q

darkly pigmented septa between 2 cells part of the outer cell wall in tinea nigra

A

annelide

25
Q

aged tinea nigra on PDA is characterized by

A

abundant aerial mycelia and velvety, dark olive in color

26
Q

tinea nigra in LPCB

A

2- celled (cylindrical and spindle-shaped) pale brown yeast cells

27
Q

piedra meaning

A

small stone

*due to firm irregular nodules

28
Q

the mass of fungus in piedra can be found in

A

hair shaft

29
Q

clinical features of black piedra

A

Discrete, hard, more compact, gritty, brown to black concretions

or nodules

30
Q

commonness of black piedra

A

Scalp hair > Beard, mustache > Axilla and groin hairs – rare

31
Q

specimen collected for black piedra

A

hair with nodules

*with 25% KOH or NaOH

32
Q

seen under direct microscopic examination for black piedra

A

→ Dark septate hyphae
→ Round to oval asci
→ Hyaline, curved to fusiform ascospore, a sexual spore

33
Q

media used to isolate black piedra

A

SDA with chloramphenicol
SDA with cycloheximide

*very slow growth and island colonies

34
Q

black piedra in isolated culture is characterized by

A

→ Dark brown to black colonies with greenish brown, short aerial mycelium

35
Q

etiologic agent of white piedra

A

Trichosporon beigelii or Trichosporon cutaneum

36
Q

t or F: white piedra commonly appears in scalp, eyebrows and lashes

A

false: face, axilla, genitals

37
Q

specimen used for diagnosis

A

hair with nodules (+ 10% KOH or 25%NaOH + 5% glycerin)

38
Q

isolation of white piedra (same as black but without cycloheximide)

A

SDA with chloramphenicol without cycloheximide (rapid)

LPCB (Hyaline hyphae, Arthroconidia, Blastoconidia)

39
Q

other characteristics of WHITE PIEDRA

A 
→ Non-carbohydrate fermenting
→ Assimilates dextrose, lactose, D-xylose and inositol
→ Negative KNO3 assimilation
→ Urease positive
→ Splits arbutin

Medical microbiology (14 decks)

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