Epidermophyton floccosum
| Epidermophyton floccosum | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Epidermophyton floccosum |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Epidermophyton floccosum | ||||||||||||
| ( Harz ) Langeron & Miloch. |
As a skin fungus from the (non- taxonomic ) group of dermatophytes, Epidermophyton floccosum is ofmedically relevant importance because it is a causative agent of skin fungal diseases. It only affects humans (anthropophilic); The skin is primarily affected( dermatophytosis ), less often the nails ( nail fungus ), but never the hair .
Macroscopic features
Both on Sabouraud glucose agar (alternatively Kimmig agar) and on Mycosel agar, the dermatophyte grows moderately quickly, initially white. But after just a few days the thallus takes on its characteristic greenish-yellow ("olive green") color. However, the range of variation is surprisingly large, so that purple or pink colored isolates are also possible. The colonies are usually flat with a central, button-like elevation and traversed by radial furrows and folds. After 10 days at 30 ° C the colony has a diameter of 10-25 mm. Typical is the so-called pleomorphism , which actually sets in after three weeks , which actually means 'the diversity'. Here it can be recognized by the white, cotton-like flakes of aerial mycelium ( see mycelium ) in the middle of the colonies. With increasing age and after just a few subcultures, the fungus becomes completely pleomorphic and consists only of white, cotton wool and so-called sterile mycelium . The underside of the primary culture is colorless, later yellow-brownish and furrowed.
Microscopic features
The microscopic picture shows numerous club-shaped, smooth-walled and thin-walled macroconidia with 2–8 chambers, which sit individually laterally on the septate hyphae or are arranged terminally to 2–5 in tufts. They can be 7–12 µm wide and 20–40 µm long. In contrast to the genera Trichophyton and Microsporum , no microconidia are formed. Depending on the age of culture, increasing intercalary and terminal chlamydospores, 20 µm in size, can be seen.
Physiological characteristics
The optimum growth is 28 ° C. The fungus also grows at 37 ° C. In contrast to other dermatophytes, E. floccosum cannot attack hair. Vitamin additives to the nutrient medium have no significant effects and can therefore be neglected. The urease test is often positive after 7 days at 25 ° C, but not always reliable. On BCP (bromocresol purple) milk glucose agar, the indicator turns purple in contrast to yellow pigmented Trichophyton rubrum strains. Stunted, pleomorphic cultures can be returned to their original, flat, greenish-yellow and macroconidia-containing growth form by inoculation on saline agar plates to which 3% or even 5% sodium chloride (NaCl) is added. This is also a distinguishing feature from other dermatophytes, which either do not grow or remain pleomorphic under these conditions.
Clinical significance
The fungus is transmitted from person to person, often indirectly via shower rooms , baths, towels, shoes and clothing (underwear and stockings). Experimental infections in laboratory animals were unsuccessful. In humans, the infection occurs most frequently in the groin and legs as tinea inguinalis et cruris, but also on the face ( tinea faciei ), on the neck , back , and abdomen as tinea corporis , on the arms , backs of the hands , palms and spaces between the fingers as tinea manus , on the soles of the feet and between the toes as tinea pedis , and much less often in the nails as tinea unguium or onychomycosis. Tinea corporis is characterized by reddening and pustular skin disorders with ring-shaped to radial spread.
Examination material and determination method
Materials that can be attacked by the fungus should be used, i.e. flakes of skin and nails, but not hair and hair roots. In addition to the direct preparation, the fungal culture is prepared from the test material on at least two different nutrient media . For the direct preparation, Calcofluor in 20 percent potassium hydroxide solution should preferably be used for digestion. In the positive case, extended chains of thick-walled, green-shining, not severely swollen, intercalar chlamydospores can be seen using a fluorescence microscope at first 100-fold, then 400-fold magnification . Since some strains of E. floccosum could possibly be inhibited by cycloheximide in the culture medium, at least one culture medium without cycloheximide should always be used.
rating
Epidermophyton floccosum is in any case a pathogenic agent that occurs fourth most frequently in Central Europe compared to other dermatophytes. Any evidence from patient material - skin and nail flakes - is to be regarded as a finding that requires therapy. The treatment is carried out externally with antimycotic creams and solutions, in the case of infection of the nails with systemic antimycotics in tablet or capsule form, including terbinafine or itraconazole .
literature
- RC Summerbell, J. Kane: The genera Trichophyton and Epidermophyton . In: J. Kane, RC Summerbell, L. Sigler, S. Krajden, G. Land: Laboratory handbook of dermatophytes . Star Publishing Company, Belmont (USA), 1997, pp. 131-191
