Introduction to Mycology and Superficial Mycoses

Question 1

ergosterol

Answer 1

Sterol found in cytoplasmic membrane of fungi

Question 2

glucan

Answer 2

component of fungal cell wall, for which echinocandins inhibit synthesis

Question 3

yeast vs mold

Answer 3

yeast are single-celled budding fungi, mold are composed of tubular structures called hyphae. Both yeast and molds form (all fungi) form spores through mitosis.

Question 4

mycelium

Answer 4

intertwined mass of hyphae

Question 5

dimorphism

Answer 5

ability for some fungi to grow as yeast at body temperature in tissue but as hyphae/molds at ambient temperatures or in culture

Question 6

Potassium Hydroxide

Answer 6

Used to disrupt surrounding tissue of scrapings and allow fungus morphology to stand out because fungal cell wall is resistant to KOH

Question 7

azoles

Answer 7

Antifungal agent that inhibits ergosterol synthesis. All are active against yeasts

Question 8

polyenes

Answer 8

Antifungal that binds to ergosterol and increases cell permeability. Topical: Nystatin, IV: Amphotericin B

Question 9

echinocandins

Answer 9

Antifungal agent that inhibits synthesis of glucan in fungal cell wall

Question 10

Pityriasis versicolor

Answer 10

Usually asymptomatic infection of stratum corneum, caused by pityrsporum furfur. Discrete, discolored skin lesions. Needs oil or fatty acids in medium for growth.

Tx: azole or Selsun Blue

Question 11

Piedra

Answer 11

Fungal infection of hair shaft, presence of firm, irregular nodules.

White: Trichosporon cutaneum
Black: Piedraia hortae

Tx: topical azole helps, but relapse is common.

Question 12

dermatophytes

Answer 12

Molds that cause infections of keratinized tissues, epidermis, hair and nails. All contain keratinase.

Question 13

microsporum

Answer 13

dermatophyte that attacks hair and skin, fluoresces green under a Woods lamp

Question 14

trichophyton

Answer 14

most common dermatophyte that attacks hair, skin and nails

Question 15

epidermophyton

Answer 15

dermatophyte that attacks skin and nails

Question 16

Tinea capitis

Answer 16

Infection of scalp, eyebrows, and eyelashes cased by microsporum and trichophyton.
Characteristics: scaly erythematous lesion and alopecia

Question 17

tinea corporis

Answer 17

stratum corneum infection in glabrous skin, commonly identified as ringworm

Annular lesion: scaly and usually tends to heal, periphery an advancing vesicular circle
Vesicular lesion: elevated inflamed margin, central scaling

Question 18

tinea cruris

Answer 18

Involves the groin, perineum, and perianal region. Thin, dry epidermal scaling that is severely pruritic. Usually tricophyton/epidermophyton.

Question 19

tinea pedis

Answer 19

Athletes foot - trichophyton most commonly involved.

Question 20

onychomycosis

Answer 20

fungal infection of nails, may be caused by dermatophytes, candida or other fungi. Treat with prolonged course of systemic therapy of terbinafine or itraconozole

Question 21

Dermatophyte treatments

Answer 21

Use topical azole agents for many of these superficial infections

Exceptions:
tinea corporis: systemic therapy of azole, or terbinafine (allylamine that inhibits sterol synthesis)
tinea capitis in children: griseofulvin (oral)

Question 22

Lab ID of dermatophytes

Answer 22

Look for branching septate mycelium under microscope.

Culture: Grow in Sabouraud medium, but ID is still difficult for species. Species ID is possible only with culture and may take weeks.

Question 23

sporotrichosis

Answer 23

subcutaneous mycosis caused by sporothrix schenckii. Think thorns from picking roses, but just about any soil or plan injury may transmit. Nodular lesions which may ulcerate.

Lymphocutaneous form: look for chain of swollen lymph nodes extending from first lesion

Lab: Look for cigar-shaped forms surrounded by asteroid body.

Dimorphic fungus, use itraconazole or amphotericin as alternative.

Question 24

Chromomycosis

Answer 24

tropical and subtropical areas, chronic granulomatous infection caused by dematiaceous fungi. If untreated may cause cauliflower lesions. No bone involvement, relapses common.

Question 25

mycetoma

Answer 25

any chronic, subcutaneous or tissue tumor caused by fungi. Brown people get madura foot. Its their faults for being foreign, its in their bones.

Mycetoma lesions may involve bones, unlike chromomycosis. Surgical excision and systemic treatment with azoles or amphotericin required.