Cutaneous and Superficial Mycoses

Cutaneous and Superficial Mycoses

• The earliest recognized infectious disease in humans
• Physicians described disease-producing microorganisms in humans during the 1840s

Infections

• Infections affect hair, skin, and nails
• Considered cutaneous infections

The particular disease

• Evidences of this disease involved cultivating the microorganism on artificial media
• Specific fungi produced isolates in healthy human skin, manifesting the same infection
• This supported Koch’s postulates, before formulation

Epidemiology

• Human-to-human transmission is mainly through contact with infected subjects, people, or animals
• Infections are common with societal shifts in population
• High prevalence in barber shops, locker rooms, and prison cells
• Handwashing is the primary preventive measure

Clinical Significance

• Low infectivity and virulence

Diagnosis

• Clinical examination involves KOH preparation for microscopic appearance of conidia and hyphae
• Cultures are not usually needed
• Hair for examination should be broken and twisted.
• Pigmentation is examined using Wood’s light
• Culture media: SDA with or without antibiotics.
• DTM shows hyphae within growth with red color within 14 days
• Media are held for 1 month

Epidermophyton (Anthrophilic)

• E. floccosum infects the nails
• On SABHI at room temperature, colonies will appear yellow with a tan reverse within 10 days
• Macroconidia are smooth/thin walled, club-shaped, contain 2-5 cells, and are numerous
• Microconidia are absent

Microsporum

• Macroconidia: large, spindle-shaped, thick-walled, and multi-septate (more than 6 cells)
• Microconidia: few (small and club-shaped) or absent
• Aerial mycelium produces powdery or velvety colonies

M. canis

• Forms numerous thick-walled, spindle-shaped macroconidia with tapered ends and 6-15 cells
• Zoophilic species found in animals
• Produces green-yellow fluorescence of ectothrix hairs

M. gypseum

• Cigar-shaped multiseptate macroconidia
• Produces numerous thin-walled, elliptical macroconidia containing 4-6 cells
• Geophilic species is found in the soil

M. audouinii

• Produces apple-green fluorescence of ectothrix hair and bizarre-shaped macroconidia
• Forms pectinate (comblike) septate hyphae with terminal chlamydoconidia often with pointed ends
• Grows poorly on rice grains, unlike other dermatophytes
• Anthropophilic species are found in humans

Trichophyton (anthrophilic)

• Infects hair, nails, and chest
• Does not fluoresce under Wood's lamp
• Macroconidia: smooth, club-shaped, thin walled, with 8-10 septa
• Microconidia: the predominant form, spherical, tear-shaped, or clavate
• Colonies may be powdery, waxy, or velvety

T. rubrum

• Has deep-cherry-red or burgundy pigment on the underside and “wine-red” soluble pigment
• Media that enhance pigment production: CORNMEAL or POTATO DEXTROSE AGAR
• Macroconidia are pencil-shaped
• Microconidia are tear-shaped, single, and lateral along the hyphae

T. mentagrophytes

• Rose or red-brown underside (scant red pigment)
• Causes ectothrix hair infections
• Macroconidia are few, smooth walled, and cigar-shaped, connected to a hypha with a narrow attachment
• Microconidia are spherical, often in grape-like clusters of spiral hyphae

T. tonsurans

• Agent of epidemic tinea capitis in children
• Endothrix infection of the hair
• Macroconidia are absent or rare
• Microconidia are many with various sizes and shapes with a flattened base; “BALLOON FORMS” are aged pleomorphic microconidia

Other Trichophyton spp.

• T. verrucosum produces only chlamydoconidia on SDA or PDA
• On thiamine-enriched media, elongated rat-tail macroconidia are produced
• Negative in the hair perforation test

Additional Trichophyton spp.

• T. schoenleinii produces favic chandeliers and chlamydospores
• T. violaceum produces swollen hyphae containing cytoplasmic granules

Pityriasis Versicolor

• Chronic mild superficial infection of the stratum corneum caused by Malassezia globosa and M. restricta
• Discrete, serpentine, hyper- or hypopigmented maculae occur on the skin, usually on the chest, upper back, arms, or abdomen
• Minimal scaling, inflammation, and irritation
• A cosmetic concern

Malassezia

• Lipophilic yeasts, mostly require lipid
• Direct microscopic examination of skin scrapings, treated with 10–20% KOH or stained with calcofluor white
• Lesions fluoresce under Wood's lamp
• Treatment involves daily applications of selenium sulfide
• Rarely causes opportunistic fungemia in patients and infants who are receiving total parenteral nutrition, due to contamination of the lipid emulsion
• Species of Malassezia are part of the microbial flora and isolated from normal skin and scalp
• Cause of or contributor to seborrheic dermatitis: Malassezia furfur
• Plays a role in atopic eczema/dermatitis syndrome

Clinical Diagnosis for Pityriasis Versicolor

• Demonstration of yeasts and short hyphal forms in KOH preparations of skin scrapings
• Lack of growth in the absence of oil or stimulation of growth by the presence of oil overlay
• Budding occurs as an enteroblastic process, with the formation of phialides
• The bud is broad-based, and collarettes may be observed with a light microscope, as a distinct, dark ring separates the mother and daughter cells

Tinea Nigra

• Superficial chronic and asymptomatic infection of the stratum corneum caused by the dematiaceous fungus Hortaea (Exophiala/Cladosporium) werneckii
• Microscopic examination of skin scrapings from the periphery of the lesion shows branched, septate hyphae and budding yeast cells with melaninized cell walls
• Lesions appear as dark (brown to black) discoloration, often on the palm
• Condition is more prevalent in warm coastal regions and among young women
• Treatment with keratolytic solutions, salicylic acid, or azole antifungal drugs

Piedra

• Endemic infection in tropical underdeveloped countries
• Axillary, pubic, beard, and scalp hair may be infected

Black Piedra

• A nodular infection of the hair shaft caused by Piedraia hortai
• Diagnosis is made by submerging hair in a solution of 25% KOH or NaOH with 5% glycerol and heating
• Microscopic examination reveals compact masses of dark, septate hyphae and round to oval asci containing 2-8 hyaline, aseptate hyphae

White Piedra

• Caused by Trichosporon species, larger, softer, yellowish nodules on the hairs
• Trichosporon ovoides causes scalp infections
• Trichosporon inkin causes most cases of pubic White piedra
• Diagnosis is made by microscopic evaluation of hair treated in 10% KOH or 25% NaOH with 5% glycerol, revealing intertwined hyaline septate hyphae breaking up into oval

Treatment for both types of Piedra

• Removal of hair
• Application of a topical antifungal agent