Epidermophyton:General Characteristics, Pathogenesis, Clinical Findings

Epidermophyton: General Characteristics, Pathogenesis, Clinical Findings, Laboratory Diagnosis,Treatment , Prevention and Control

Epidermophyton General features

Epdidermophyton is one of the members of dermatophytes. Dermatophytoses (tinea or ringworm): It is the most common superficial mycosis affecting skin, hair, and nails. These are closely related keratinophilic fungi ( three genera, Trichophyton, Microsporum, and Epidermophyton), which are capable to invade keratinized tissues of the skin and its appendages and are correctively known as Dermatophytes. Characteristics of dermatophytes are as follows:

Filamentous fungi, digest keratin.
Do not invade living tissues.
They are incapable of penetrating subcutaneous tissue.

Morphological classification

Dermatophytes are hyaline septate molds with more than a hundred species described. These are divided into three main anamorphic genera depending on their morphological characteristics, according to shape and site infections.

Trichophyton:- pencil-shaped, infect skin, hair, nails e.g. T. rubrum T. mentagrophytes, T. tonsurans, T. violaceum.

Microsporum:- spindle-shaped, infect skin and hair e.g. M. audouinii, M. canis, M. equinum, M. gypseum

Epidermophyton:- Club shaped, infect skin and nails e.g. E. floccosum and E. stockdaleae

Ecological classification

Depending on the usual habitat (Humans, animals, and soil).

Anthrophilic :- infected Humans. e.g. T. rubrum ,T. mentagrophytes, T. schoenleinii, T. tonsurans, T. violaceum , M. audouinii and E. floccosum
Zoophilic:- infect animals as well as birds. e.g. T.equinum, T. verrucosum, M. canis and M. equinum
Geophilic:- frequently isolated from soil. e.g. T.ajelloi , M. gypseum , E. stockdaleae

Epidermophyton floccosum

Epidermophyton floccosum is an anthropophilic dermatophyte with a cosmopolitan distribution that often causes tinea pedis, tinea cruris, tinea corporis, and onychomycosis ( nail infection). E. floccosum is not known to invade hair in vivo and no specific growth requirements have been reported.

Risk Group

RG-2 organism

Morphology of Epidermophyton floccosum

Colonies of E. floccosum are usually slow-growing, greenish-brown or khaki-colored with a suede-like surface, raised and folded in the center, with a flat periphery and submerged fringe of growth but above image lacking such properties due to being young culture ( 9 days of incubation at 25°C). Older cultures may develop white pleomorphic tufts of mycelium. A deep yellowish-brown reverse pigment is usually present. Microscopic morphology shows characteristic smooth, thin-walled macroconidia which are often produced in clusters growing directly from the hyphae (specific feature- having racquets hyphae as shown above image). Numerous chlamydospores are formed in older cultures while microconidia are not formed.

Pathogenesis of Epidermophyton floccosum

Epidermophyton is a keratinophilic filamentous fungus. The ability to invade keratinized tissues and the possession of several enzymes, such as acid proteinases, elastase, keratinases, and other proteinases are the major virulence factors of these fungi.

Clinical Manifestations of Epidermophyton

Tinea pedis or Athlete’s foot: It is the ringworm, fungal infection of feet involving interdigital webs and sole. The most common clinical finding is an intertriginous form associated with maceration, scaling, fissuring, and erythema which presents with itching and burning sensation. The most common causative agents are E. floccosum, T. rubrum and T. mentagrophytes. It is common among athletes and office workers and due to the constant wearing of shoes with synthetic nylon socks which does not absorb sweat.

Tinea cruris or Jock itch or Dhobie’s itch: It is ringworm of the inguinal area involving the groin, perianal, perineal areas often involving the upper thigh. Common species of dermatophytes involved are T. rubrum, T. mentagrophytes, and E. floccosum. It is mainly seen among students as they mostly wear synthetic tight undergarments in which sweat does not get absorbed and long-standing moisture predisposes to fungal infection.

Tinea corporis: Ringworm of glabrous skin. The lesions are well marginated with raised erythematous borders. The annular, scaly patches may coalesce to form a large area of chronic infection. The common causative agents of dermatophytes are T. rubrum, T. mentagrophytes, T. tonsurans but also the involvement of E. floccosum. It is observed to be predominant among people with a previous family history of disease and it may be transmitted by direct contact with other infected individuals. Tinea capitis is the second most important clinical type seen among people with a previous family history of the disease. It is because these diseases may be transmitted through fomites such as comb, hairbrushes, bedding, pillows, clothes, towels or furniture, etc. In addition, tinea corporis can be attributed to poor personal hygiene and heavy manual work.

Tinea unguium or onychomycosis: It is the ringworm infection of the nail plate. Distal subungual infection is the commonest pattern and involves the nail bed and underside of the nail in the distal portion. The nail plate is brittle, friable, thickened, and may crack because of piling up of subungual debris. The color of the nail becomes often brown or black. The commonest species responsible for causing onychomycosis are tinea unguium are T. rubrum, T. mentagrophytes, and E. floccosum. It is common among housewives and servant maids due to the practice of cleaning the cowshed bare-handed, washing the household utensils with ash, and frequent dipping of hands in soap water; all of which enhance the chances of fungal infection.

Laboratory Diagnosis of Epidermophyton infections

Specimen: Skin scrapings, nail scrapings

Microscopic Examination

10–20% potassium hydroxide, with or without calcofluor white, and the specimens skin or nails.

Cultural Examination

Using inhibitory mold agar or SDA medium containing cycloheximide and chloramphenicol which suppresses mold and bacterial growth. Colonies are usually slow-growing, greenish-brown or khaki-colored with a suede-like surface, raised and folded in the center, with a flat periphery and submerged fringe of growth.

LPCB Tease mount for Microscopic appearance

The colony is teased and the LPCB mount is made to demonstrate the hyphae and spore ( conidia). Conidia is of two types i.e. Microconidia:- small unicellular

Macroconidia:- Multicellular, septate

Special hyphae:- hyphae such as racquet hyphae as shown above picture.

Biochemical test

Urease test:- Epidermophyton species are urease negative

Other methods of diagnosis

Hair perforation test:- fungi pierce hair-producing wedge-shaped perforations.

Positive:- Trichophyton mentagrophytes and Microsporum canis.

Negative: Epidermophyton species

Molecular methods

PCR assay: A variety of PCR assays are applicable, among them some are-

PCR-Restriction Fragment Length Plormophism (PCR-RFLP) is used to distinguish the 12 species that cause dermatophytosis infections.
Real-time PCR is also used to identify E. floccosum after fungal lysis

Treatment of Epidermophyton infections

Tnea pedis, tinea cruris and tinea corporis are treated tropically using naftifine, terbinafine, butenafine, clotrimazole, ketoconazole,econazole miconazole,sulconazole, oxiconazole, cyclopyrox, and tolnaftate while
tinea unguium or onychomycosis(nail infections), topical therapy is normally unsuccessful, and thus, the use of systemic oral therapy for a prolonged period is advised.

Prevention and control Epidermophyton infections

Avoiding touching lesions on the skin and nails of infected people.
Wearing loose-fitting clothing on the affected areas.
Practicing good hygiene when engaging in activities that involve close human contact with skin

Key Notes

Trichophyton rubrum is the commonest causative agent of dermatophytoses worldwide.
Trichophyton species may cause invasive infections in immunocompromised hosts.
Antropophilic species are highly contagious between humans
Males more commonly infected as progesterone is inhibitory to dermatophyte growth.

universe84a