Superficial mycoses- Tinea nigra, Piedra

 Superficial Mycoses

(1) Pityriasis versicolor

• Common superficial mycoses caused by a lipophilic yeast Malassezia furfur 
• Chronic usually asymptomatic involvement of stratum corneum 
•  Normal flora of skin - so the disease re-occurs.
• common in the tropics with more than 60 % of the population infected-young adults mainly
• Cause opportunistic infection in normal skin
• Multiple patchy well-demarcated lesions (oval shape) hypo or hyper pigmented -either light in color or brown -
• Scattered over the back, neck, chest, shoulders - Seldom the face.
  

Predisposing factors:

• Humidity –Immunosuppression –Poor hygiene – Sweat – Greasy skin – Chronic bacterial infections – Steroids
• Affects the epidermal area with strong affinity to keratin

Diagnosis:

• Skin scraping using scalpel (sharp bladed instrument) followed by 10% KOH preparation (skin scrapings placed into 10% KOH , which will destroy skin cells and only fungal cells are retained)

Sampling  can be done with Wood ́s lamp (producing ultraviolet radiation) -uses ultraviolet (UV) light to look at the skin closely. Normally, the light will look purple or violet and skin will not fluoresce (glow) or show any spots under the Wood’s lamp. Skin will change color there is fungal infection 

• Direct Microscopy – abundant yeast-like cells and short branched hyphal filaments- “Spaghetti and meatballs”

• Culture: Malassezia furfur (Lipophilic) can be grown in a laboratory only if the culture is covered with oil. --Sabouraud Dextrose Agar flooded with Olive oil

    Dixon's agar- A specialized isolation medium containing glycerol-mono-oleate for primary isolation of Malassezia furfur 

  Tinea nigra

Localized chronic superficial fungal infection of stratum corneum of the palms and soles- brown to black macules– found mainly in the tropics

Caused by Cladosporium werneckii/Hortae werneckii/Exophiala werneckii

Laboratory Diagnosis

Direct Microscopy of 10% KOH preparation of Skin scrapings - pigmented brown to dark septate hyphal elements and budding yeast cells

Culture: Primary isolation media is Sabouraud's dextrose agar - colonies are mucoid, yeast-like grey or black

 Piedra

fungus infection of the hair-characterized by the appearance of firm, irregular nodules along the hair shaft- nodules are fungal cells cemented together with the hair

Two varieties-

Black piedra – caused by Piedra hortae - Chronic fungal infection of the hair shaft  mostly affects young adults  epidemics in families-Infected hairs: hard black nodules on the shaft •

Direct Microscopy: – 10% KOH • darkly pigmented nodules in hair shaft –asci detected

Culture: – On SDA, colonies are dark, brown-black -Take about 2-3 weeks to appear

White piedra – caused by Trichosporon beigelii –  common in young adults - Nodules: white, follicles– irregular, soft, white or light brown nodules adhering to the hairs

   Direct Microscopy: – 10% KOH – Arthrospores

2.   Culture: primary isolation media – white or yellowish to deep cream colored – smooth, wrinkled, velvety, dull colonies with a mycelial fringe. Laboratory Diagnosis