Introduction to Mycology and Superficial Mycoses Flashcards
ergosterol
Sterol found in cytoplasmic membrane of fungi
glucan
component of fungal cell wall, for which echinocandins inhibit synthesis
yeast vs mold
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.
mycelium
intertwined mass of hyphae
dimorphism
ability for some fungi to grow as yeast at body temperature in tissue but as hyphae/molds at ambient temperatures or in culture
Potassium Hydroxide
Used to disrupt surrounding tissue of scrapings and allow fungus morphology to stand out because fungal cell wall is resistant to KOH
azoles
Antifungal agent that inhibits ergosterol synthesis. All are active against yeasts
polyenes
Antifungal that binds to ergosterol and increases cell permeability. Topical: Nystatin, IV: Amphotericin B
echinocandins
Antifungal agent that inhibits synthesis of glucan in fungal cell wall
Pityriasis versicolor
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
Piedra
Fungal infection of hair shaft, presence of firm, irregular nodules.
White: Trichosporon cutaneum
Black: Piedraia hortae
Tx: topical azole helps, but relapse is common.
dermatophytes
Molds that cause infections of keratinized tissues, epidermis, hair and nails. All contain keratinase.
microsporum
dermatophyte that attacks hair and skin, fluoresces green under a Woods lamp
trichophyton
most common dermatophyte that attacks hair, skin and nails
epidermophyton
dermatophyte that attacks skin and nails
Tinea capitis
Infection of scalp, eyebrows, and eyelashes cased by microsporum and trichophyton.
Characteristics: scaly erythematous lesion and alopecia
tinea corporis
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
tinea cruris
Involves the groin, perineum, and perianal region. Thin, dry epidermal scaling that is severely pruritic. Usually tricophyton/epidermophyton.
tinea pedis
Athletes foot - trichophyton most commonly involved.
onychomycosis
fungal infection of nails, may be caused by dermatophytes, candida or other fungi. Treat with prolonged course of systemic therapy of terbinafine or itraconozole
Dermatophyte treatments
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)
Lab ID of dermatophytes
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.
sporotrichosis
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.
Chromomycosis
tropical and subtropical areas, chronic granulomatous infection caused by dematiaceous fungi. If untreated may cause cauliflower lesions. No bone involvement, relapses common.
