VI. CUTANEOUS AND SUPERFICIAL FUNGI

• Are infections that involve the outer epithelial layers of the skin and top layers of the hair and nails.

Superficial mycoses

Involve deeper layers of the skin and more tissue.

Cutaneous mycoses

The term used to group the various fungi that cause infections (dermatophytoses) of the skin, hair, and nails.

Dermatophyte

• The dermatophytes are _____ (i.e., able to metabolize keratin).

• Dermatophytes contain three genera.

     1) Trichophyton: Infects _____

     2) Epidermophyton: Infects ____

     3) Microsporum: Infects ____

• Dermatophyte infection is termed ___.

• keratinophilic

1. nails, hair, and skin

2. skin and nails

3. hair and skin

• tinea

• An infection of the spaces between the toes

• Characterized by itching and scaling

Tinea pedis or athlete’s foot

Tinea pedis or athlete’s foot

Caused by Trichophyton spp. and Epidermophyton spp

• An infection of smooth skin

• Characterized by circular patches of scaly skin

Tinea corporis or ringworm:

Tinea corporis or ringworm:

Caused by Microsporum spp. and Trichophyton spp.

• An infection of the nails

• Characterized by discoloration, thickening, and progressive destruction of the nails

Tinea unguium or onychomycosis

Tinea unguium or onychomycosis

Caused by Epidermophyton spp. and Trichophyton spp.

• An infection of the scalp

• Characterized by circular bald patches on the scalp

Tinea capitis

Tinea capitis

Caused by Microsporum spp. and Trichophyton spp

• An infection of beard hair

• Characterized by skin lesions

Tinea barbae or barber’s itch

Tinea barbae or barber’s itch

Caused by Microsporum spp. and Trichophyton spp.

• An infection of the groin

• Characterized by itching and scaling of the groin area

Tinea cruris or jock itch

Tinea cruris or jock itch

Caused by Trichophyton spp. and Epidermophyton spp.

• Identification of the dermatophytes is primarily based on colony morphology and microscopic appearance.

• In some cases, it may be necessary to perform an in vitro ___.

• Sterile hair is infected with the isolated fungus and after incubation is examined microscopically for _____ perforations.

• hair perforation test

• wedge-shaped

Colony characteristics: Two colony types will be seen between 7 and 10 days on SABHI at room temperature.

• Buff granular colonies, rose to tan colored, with a yellow, brown, or red reverse

• White fluffy colonies with a colorless to yellow reverse

Trichophyton

Microscopic characteristics

• Macroconidia are smooth/thin walled, pencil shaped, contain three to seven cells, and are few in number.

• Microconidia are round to club shaped in grapelike clusters and are few to numerous in number.

Trichophyton

Species identification: Trichophyton

• Characteristically produces grapelike clusters of microconidia.

• Some strains produce numerous macroconidia

• Positive in the hair perforation test.

Trichophyton mentagrophytes

Species identification: Trichophyton

• Produces few or numerous macroconidia; numerous club-shaped microconidia are borne singularly on the hyphae.

• Forms deep red reverse on PDA.

• Negative in the hair perforation test

Trichophyton rubrum

Species identification: Trichophyton

• Produces only chlamydoconidia on SDA or PDA.

• On thiamine-enriched media, elongated rat-tail macroconidia are produced.

• Negative in the hair perforation test.

Trichophyton verrucosum

Culture characteristics: On SABHI at room temperature, colonies will appear yellow with a tan reverse within 10 days

Epidermophyton

Microscopic characteristics

• Macroconidia are smooth/thin walled, club shaped, contain two to five cells, and are numerous in number.

• Microconidia are not present.

_______ invades nails, and on KOH preparation chains of arthroconidia can be seen.

Epidermophyton

Epidermophyton floccosum

At room temperature on SDA, E. floccosum forms _____ colonies with tan reverse.

khaki-yellow

Colony morphology: On SABHI at room temperature, colonies will be light tan, with a salmon-colored reverse, are very slow growers.

Microsporum

Microscopic characteristics

• Macroconidia are rough/thin to thick walled, spindle shaped, contain 4–15 cells, and are numerous in number.

• Microconidia are club shaped, single, and few in number.

Microsporum

Species identification: Microsporum

•  Forms pectinate (comblike) septate hyphae with terminal chlamydoconidia often with pointed ends.

• Unlike other dermatophytes, this species grows poorly on rice grains. 

• It is an anthropophilic (found in humans) species.

Microsporum audouinii 

Species identification: Microsporum

• Forms numerous thick-walled, spindle-shaped macroconidia with tapered ends and 6–15 cells.

• It is a zoophilic species (found in animals).

Microsporum canis

Species identification: Microsporum

• Produces numerous thin-walled, elliptical macroconidia containing four to six cells.

• It is a geophilic species (found in the soil).

Microsporum gypseum

• Infection of the stratum corneum caused by lipophilic yeast

• Infection commonly occurs on the upper back, chest, shoulders, upper arms, and abdomen.

• There may be an association between the disease and excessive sweating.

Tinea (pityriasis) versicolor

Causative agent of Tinea (pityriasis) versicolor

Malassezia furfur complex

• Diagnosis is made by KOH preparation of skin scrapings from the lesions that demonstrate characteristic yeastlike cells and hyphae (spaghetti and meatballs).

• Most lesions will fluoresce yellow under a Wood’s lamp.

Tinea (pityriasis) versicolor

• Characterized by the presence of brown to black nonscaly macules on the palms of the hands and less commonly the dorsa of the feet

Tinea nigra

• The presence of numerous light brown, frequently branching septate hyphae and budding cells (some with septates) on KOH preparations is suggestive of infection

Tinea nigra

Causative agent of Tinea nigra

Hortaea werneckii;

• A fungal infection of the scalp hair and less frequently the beard, mustache, and axillary and pubic hairs.

• The disease is characterized by the presence of hard, dark nodules on the hair shaft.

Black piedra

• Diagnosis can be made by submerging hair in a solution of 25% KOH or NaOH with 5% glycerol and heating.

• Microscopic examination will reveal compact masses of dark, septate hyphae and round to oval asci containing two to eight hyaline, aseptate banana-shaped ascospores.

Black piedra

Causative agent of Black piedra

Piedra hortaea

• A fungal infection of facial, axillary, or genital hairs and less commonly the scalp.

• It is characterized by the presence of soft, white, yellowish, beige, or greenish nodules on the hair shaft.

White piedra

• Microscopic evaluation of hair treated in 10% KOH or 25% NaOH with 5% glycerol reveals intertwined hyaline septate hyphae breaking up into oval or rectangular arthroconidia.

• Culture characteristics of the Trichosporon spp. were previously discussed with the yeasts.

White piedra

Causative agent of White piedra

• Trichosporon ovoides is the causative agent of scalp infections

• Trichosporon inkin causes most cases of pubic white piedra.