Mycology

Superficial Mycoses

Lec:2 Dr,Huda
تسلسل11 المرحلة الثالثة جراثيم نظري العدد8 19\3\2018

Superficial Mycoses

Limited to the outermost layer of the skin 4 Infections 1.Pityriasis versicolor 2.Tinea nigra 3. Black piedra 4. White piedra

Pityriasis Versicolor

Malassezia furfur (Pityrosporum orbiculare) is the causative agents. Lipophilic yeast like organism Rich in sebaceous glands Media is supplemented with fatty acids Exist in budding yeast,occasionally hyphal

A chronic, superficial fungal disease of the skin characterized by well-demarcated white, pink, fawn, or brownish lesions, often coalescing, and covered with thin scales. The colour varies according to the normal pigmentation of the patient, exposure of the area to sunlight, and the severity of the disease.
Pityriasis (tinea) versicolor

Lesions occur on the trunk, shoulders and arms, neck but rarely on the face, and fluoresce a pale greenish colour under Wood's ultra-violet light. Young adults are affected most often, but the disease may occur in childhood and old age. World-wide in distribution but more common in tropical than temperate climates.

350



Seborrhoeic dermatitis and dandruff: Current evidence suggests M. furfur, combined with multifactorial host factors is also the direct cause of seborrhoeic dermatitis, with dandruff being the mildest manifestation. Host factors include genetic predisposition, an emotional component (possible endocrine or neurologically mediated factors), changes in quantity and composition of sebum. Lesions are red and covered with greasy scales and itching is common in the scalp.

Fungaemia

M. furfur has also been reported as causing catheter acquired fungaemia in neonate and adult patients undergoing lipid replacement therapy. Such patients may also develop small embolic lesions in the lungs or other organs.


Follicular pityriasis versicolor Lesions are visible around the hair follicles and sebaceous glands. This is a more severe form of the disease

Laboratory diagnosis

Skin scraping & KoH (10%)exam. glycerol and Parker ink solution Under microscope , thick-walled round, budding yeast-like cells and short angular hyphal forms up to 8um in diameter(spaghetti and meat balls). Culture is only needed in cases of fungaemia . Overlay Sabouraud's dextrose agar containing cycloheximide (actidione) with olive oil .


359

Tinea Nigra

Exophiala werneckii is the causative agents.Produce melanin black or brown colorGrows as yeast  Older hyphae with mycelia and conidia


Tinea nigra
Lesion- gray to black macular palms Diagnosis- Skin scrapings with alkali stain Cultures- Sabourauds’s media pigmented yeast and hyphae

Black piedra

Piedraia hortae-is the causative agent Clinical feature: presence of hard nodules found along the infected hair shaft Nodules contain asci

Cultures - older cultures teleomorphic (asci ,which contain spindle shaped ascospores)

White Piedra

Trichosporon beigelii is the causative agents. Hair- soft ,pasty,cream colored growth Microscopy : septate hyphae that develop into arthroconidia

White Piedra

Grows in media without cyclohexamideCultures are pasty and white developed deep radiating furrows and become yellow and creamyMicroscopic examination septate hypae that develops into arthroconidia

Superficial mycoses: Trichosporon beigelii Cause of white piedra. Piedraia hortae Cause of black piedra.

Treatment

Skin removal of the organism by: 1.Selenium sulfide 2.Thiosulfate 3.Salicylic acid 4.Hyposulfite 5-inhibition of ergosterol by: miconazole

Cutaneous mycoses

Skin , hair & nailsEvoke cellular immune responseDermatophytes(keratophilic)Clinical manifestationsringworm or tinea. Etiology MicrosporumTrichophyton Epidermophyton

General characteristics of Macroconidia and Microconidia of Dermatophytes

Genus
Macroconidia
Microconidia
Microsporum
Numerous, thick walled,rough
Rare
Epidermophyton
Numerous, smooth walled
Absent
Trichophyton
Rare,thin walled, smooth
Abundant

Microsporum

Trichophyton

Cutaneous mycoses
Classifications: Anatomic location Tinea pedis Tinea capitis Tinea corporis Tinea cruris Ecologic location Geophilic (from soil) Zoophilic (animal) Anthropophilic (human)

Cutaneous mycoses

Diagnosis
Diagnosis is based upon: 1. Anatomical site infected 2. Type of lesion 3. Examination with a Woods lamp 4. Examination of KOH-treated skin,hair & nail scales 5-Culture of the organism (Identification based on the conidia).

Differential diagnosis