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Microbiology Unit 3 > 5 Dermatomycoses > Flashcards

5 Dermatomycoses Flashcards

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1
Q

Which species are considered cutaneous fungi?

A

Malassezia furfur

Hortaea werneckii

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2
Q

How are dermatophytes different from cutaneous fungi?

A

Pathogenic fungi
Require keratin for growth (hair, nails, skin)
Do not infect mucosal surfaces
Secrete keratinase (allows for inhabiting keratinized regions of the body)

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3
Q

Important genera of dermatophytes

A

Epidermophyton
Microsporum
Trichophyton

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4
Q

What makes dermatophytes morphologically identifiable?

A

Hyphae and arthoconidia can be visualized in dead keratinized tissue

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5
Q

How do you culture dermatophytes for diagnosis?

A

If onychomycosis, culture material under nails

Sabouraud agar at room temp for 1-3 weeks

DERMATOPHYTES TEST MEDIUM (DTM) allows for early detection

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6
Q

How does Dermatophytes test medium work?

A

Selective (cyclohexamide and abx) and differential (color change based on fermentation of sugars)

Dermatophytes utilize nitrogenous compounds preferentially over carbs

Change in pH (alkaline) —> red color change

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7
Q

What is the infective stage of dermatophyte?

A

Arthroconidium - can be visualized microscopically in 10% KOH wet mount

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8
Q

How is the morphology of Trichophytin different?

A

Galactomannan peptide

Crude antigen of dermatophytes
• CHO component-intermediate response
• Peptide component-delayed response

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9
Q

How does 10% KOH work?

A

Digests human tissue, leaves fungal components intact

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10
Q

What classification of dermatophyte:

Animal pathogens that may be transmitted to people

A

Zoophilic

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11
Q

What classification of dermatophyte:

Human transmission

A

Antrophophilic

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12
Q

What classification of dermatophyte:

Transmitted through soil to people

A

Geophilic

Usually invade non-viable keratinized tissue

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13
Q

What are the favored habitats for dermatophytes?

A

Moist areas of the body

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14
Q

What parts of the world will you find dermatophyte infections?

A

Worldwide, but most prevalent in the tropics

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15
Q

What are arthrospores?

A

Fragment hyphal elements in hair, nails, outer skin

Also see infections by microconidia, macroconidia, and sexual spores

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16
Q

How do dermatophyte infections typically present in people?

A

Lesions are inflamed at edges, with a central clearing zone

Hair loss with itching, but not debilitating

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17
Q

Predisposing factors for dermatophytosis?

A

Nail trauma, HIV, DM, immunosuppressive meds

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18
Q

Risk factors for dermatophytosis

A

Communal bathing facilities, immunocompromised status, Cushing syndrome (increased cortisol interferes with inflammation) and some contact sports (ie wrestling)

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19
Q

Disseminated disease from dermatophytes is possible in …

A

HIV patients

Typically T. mentagrophytes and M. canis

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20
Q

What are the different fungal elements you might see on KOH?

A

Arthrospores (arthroconidia) - the infectious element, survives in environment

Microconidia

Macroconidia (usually multicellular)

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21
Q

What is Dermatophytid?

A

“Id reaction”

Allergic dermal reaction to fungal antigens occurring in areas devoid of organisms

Most common in Tinea pedis

Sometimes a result of excessive treatments or pruritis

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22
Q

How is dermatophytid treated?

A

As an allergy

Corticosteroids (systemic or topical)
Wet compresses
Antihistamines (systemic or topical)

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23
Q

How do you treat dermatophyte infections?

A

Antifungal agents
• Azole creams (miconazole, clotrimazole)
• Systemic antifungals (terbinafine, itraconazole)

Laser and removal of the infected tissue (ie nail)

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24
Q

How do azoles and terbinafine work in treating fungal infections?

A

Interfere with sterol synthesis in the cytoplasmic membrane of the fungus

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25
Q

Control measures to prevent dermatophyte infection

A

Good personal hygiene

Keep skin as dry as possible

Spores are shed on skin and hair (regular housecleaning important)

Spores are generally susceptible to common disinfectants, chlorine bleach, and detergents

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26
Q

What are the clinically relevant species of Trichophytons?

A

T. tonsurans
T. rubrum
T. mentagrophytes**

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27
Q

How are trichophytons distinguishable from other dermatophytes?

A

Not often fluorescent

All make pencil-shaped macroconidia with thin walls

Produce hyphae (spindle shaped), microconidia, macroconidia

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28
Q

Most common of cause of tinea capitis

A

Microsporum canis

Can also be due to T. mentagrophytes or T. tonsurans

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29
Q

What makes microsporum species identifiable?

A

Fluorescence when examined with a wood’s lamp

Produce hyphae, microconidia, macroconidia (large, spindle shaped; multicellular; thick walled)

30
Q

Name the area affected:

Tinea barbae

A

Beard

31
Q

Name the area affected:

Tinea capitis

A

Scalp

32
Q

Name the area affected:

Tinea corporis

A

Arm, leg, torso

33
Q

Name the area affected:

Tinea cruris

A

Groin

34
Q

Name the area affected:

Tinea manus

A

Hand

35
Q

Name the area affected:

Tinea pedis

A

Foot

36
Q

Name the area affected:

Tinea unguium

A

Nails

37
Q

Tinea capitis is mostly a ________ disease

A

Childhood

Involves the hair and scalp

38
Q

Endothrix ringworm infections are usually from…

A

Trichophyton

39
Q

Ectothrix ringworm infections are usually from…

A

Microsporum

40
Q

Black dot ringworm gets its appearance from…

A

Broken hair follicles

Infected hair can break off leading to alopecia

Intense inflammation, scarring and permanent alopecia can occur

41
Q

Tinea capitis can be acquired from…

A

Kittens and puppies (zoonotic)

42
Q

What is a good systemic treatment for tinea capitis?

A

Griseofulvin

43
Q

Agents that cause tinea pedis?

A

E. floccosum, T. mentagrophytes, T. rubrum

44
Q

Tinea pedis is characterized by …

A

Itching, peeling, and cracking of the skin, usually toe webs and soles

45
Q

Most prevalent of all dermatophytoses

A

Tinea pedis

46
Q

Predisposing factors for tinea corporis and tinea cruris?

A

Diabetes, obesity, excessive perspiration

Transmission can be either direct or indirect (contaminated objects like towels, clothing, bed linens)

47
Q

What gender is more commonly affected by tinea corporis/cruris?

A

Men

48
Q

Tinea unguium is another name for …

A

Onychomycosis (ringworm of the nail)

Finger and toenails become discolored and thick

May be mistaken for psoriasis

49
Q

Tinea unguium is commonly caused by…

A

E. floccosum, T. mentgrophytes, T. rubrum

50
Q

Tinea unguium usually has ______ involvement as well

A

Fungal (candida)

51
Q

Preferred treatment for tinea unguium

A

Systemic antifungals better than topical agents

52
Q

Most commonly encountered opportunistic mycoses worldwide

A

Candidiasis

Normal flora of the skin, mucous membranes that colonize mucosal surfaces soon after birth

53
Q

Underlying causes of candidiasis

A

Absence of competing normal flora

Introduction to abnormal site

Pathologic change in microenvironment

Inborn or acquired immune defect

Use of broad-spectrum abx

54
Q

What factor helps Candida albicans adhere the most?

A

Germ tube more adhesive than yeast cell

Not many virulence factors other than that

55
Q

How is candida diagnosed?

A

Direct microscopic exam —> gram stained samples show large G(+) cells

Will also see yeast cells, pseudohyphae, and true hyphae

56
Q

What kind of culture can you do for candida?

A

Chromagar (will show hyphae and pseudohyphae in addition to germ tubes)

57
Q

Why is serology difficult for candida?

A

It’s normal flora

Many have had prior exposure

Low tigers of antibody

58
Q

How do you treat candida?

A

Topical cream (miconazole) or oral fluconazole

59
Q

Tinea versicolor is caused by…

A

Malassezia furfur (cutaneous fungi)

60
Q

What does Malassezia furfur look like?

A

Microscopically: short, unbranched hyphae and somewhat spherical cells (SPAGHETTI AND MEATBALLS)***

61
Q

Malassezia furfur has what growth factor?

A

Lipophilic

Requires fat to grow —> likes sebaceous glands

62
Q

Who is more commonly affected by tinea versicolor?

A

Young adults

Occurs worldwide but more common in the tropics

63
Q

What does a tinea versicolor infection look like?

A

Lesions occur as a macular patch of depigmented or hyperpigmented skin that may enlarge

Can lead to dandruff as well

64
Q

Diagnosis of tinea versicolor is via…

A

Microscopic exam of skin scrapings in KOH

65
Q

Treatment for tinea versicolor

A

Topical selenium sulfide, miconazole

66
Q

Tinea nigra is a cutaneous fungi caused by …

A

Hortaea werneckii

67
Q

What distinguishes Hortaea werneckii from other species?

A

Dimorphic species (can grow as yeast and/or mold)

Can grow in saturated salt solutions (extreme halotolerance)

68
Q

How does tinea nigra present?

A

Brownish lesion (fungus produces melanin)

69
Q

How do you diagnosis tinea nigra?

A

KOH and microscopy

70
Q

Treatment for tinea nigra?

A

Tincture of iodine or azole creams

Microbiology Unit 3 (10 decks)

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