Fungal Infections of Skin - Microbiology

Pathogenesis of Mycetoma

1. Causative agents enter through skin injuries 2. Slowly progresses to nearby tissues but spares tendons and nerves 3. Usually occurs in healthy immunocompetent individuals 4. The grains are large aggregates of microbial filaments

Laboratory Diagnosis of Mycetoma

1. KOH smear of grain 2. Gram stain

Lab Diagnosis of Dermatophytosis

1. Microscopy of KOH preparation of skin scrapings, nail clippings, and uprooted hair. 2. KOH dissolves the keratin, but cannot dissolve the fungus due to chitin in its cell wall. 3. Then culture is done to determine the species of the fungus.

Predisposing Factors of Tinea Cruris

1. Persistent sweating 2. High humidity 3. Irritation of skin from clothes, such as tight fitting underwear

5 Dermatophytosis

1. Tinea pedis (Athlete's foot) 2. Tinea unguim (fingernails and toenails) 3. Tinea corporis (arms, legs, trunk) 4. Tinea cruris (jock itch) 5. Tinea capitis (the scalp)

Tinea Pedia

Dermatophytic infection of foot. Between toes or toe webs. 4th and 5th toe most common.

Morphology of Mycetoma

Eumycteoma - Broad fungal hyphae Actinomycetoma - Thin gram positive branching bacterial filaments

Causative Agents of Mycetoma

Fungi 1. Eumycetoma 2. Dematiaceous fungi (produces mealnin in cell walls) Aerobic Actinomycetes 1. Actinomycetoma

Mycetoma foot/Maduramycosis

Mycetoma is a chronic subcutaneous infection caused by actinomycetes or fungi. This infection results in a granulomatous inflammatory response in the deep dermis and subcutaneous tissue, which can extend to the underlying bone, hence inflammed region in xray. More common in males.

Tinea Versicolor Definition

Not classic ringworm since not caused by dermatophytes. Instead caused by lipophilic fungus Malassezia Furfur. This fungus lives in the sebaceous glands of the skin as normal flora. Produces carboxylic acid which inhibits melanin production.

Tinea Versicolor Clinically

Numerous white patches on the skin of shoulders and upper back. Lesions are not itchy.

Tinea Corporis

Restricted to stratum corneum of smooth skin. Ring like lesions on skin. In severe cases these lesions are raised and become inflamed.

Tinea Versicolor Morphology

Spaghetti and meatball appearance.

Superficial Mycoses

Tinea versicolor.

Candidiasis of Skin

Yeast infection that occurs in moist areas of skin, particularly in skin folds. IN children causes napkin rash. Lesions are itchy and painful. Candidiasis of skin can occur in diabetic adults and immunodeficient patients also.

Definition of Dermatophytosis

1. Fungal infection of the skin, commonly referred to as 'ringworm'. 2. Caused by several different species of fungi. 3. Dermatophytes are the fungi that causes the parasitic infection, they feed on keratin. These fungi thrive on warm and moist skin, but may also survive directly on the outsides of hair shafts or in their interiors.

Dermatophytosis Clinically

1. Involved the keratinized part of epidermis, nails, and hair 2. Erythema and itching due to allergic reaction to fungus and toxic fungal metabolites 3. Hair loss where scalp is involved 4. Deforms the nail plate where it's involved

Causative agents of Dermatophytosis

1. Trichophyton - Infection of skin/nail/hair 2. Epidermophyton - Infection of skin/nail 3. Microsporum - Infection of skin/hair 4. All three frungi are keratinophilic

3 Main Clinical Features of Mycetoma

1. Tumor like swelling 2. Multiple draining sinuses (pus and granules come out from sinuses upon pressing the swelling) 3. Presence of grains in the sinsuses

Tinea Cruris

More common in men than women. Infection seen on scrotum and inner thigh.