Scanning electron microscopic observation on the parasitic form of the fungi in the horny layer in dermatophytosis

Electron microscopic techniques have been widely used to investigate the pathogenesis of dermatophytosis. In this article, morphological studies by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) concerned with the dermatophyte infection process are literary reviewed and we introduced our morphological study observing the parasitic form of dermatophytes in the lesional cornified layer. Various experimental models have been established to study fungal adhesion and invasion to the skin surface in the early stage of infection by several authors.In these studies, arthroconidial adherence to corneocytes and germination was demonstrated by SEM and TEM. To understand the host-fungus relationship in dermatophytosis, it is also important to identify parasitic forms of fungi and morphological changes of corneocytes in the lesion. The three-dimensional structure of growing or parasitic dermatophytes in the lesional cornified cell layer was observed using the adhesive strip method in tinea cruris and tinea glabrosa. In tinea unguium, however, it is difficult to apply this method because of subungual hyperkeratosis. We introduce the alkaline treatment method for SEM for use in observing fungal elements in a subungual hyperkeratotic lesion and scales in dermatophytosis. With this technique, small pieces of nails or scales were fixed with 2.5% glutaraldehyde, and were treated with low concentrations of alkaline and subjected to the conventional procedure for SEM observation. This method is applicable to various skin lesions, such as tinea unguium, tinea pedis and tinea capitis to investigate the parasitic forms of dermatophytes and the spatial relationship with corneocytes and is useful to understand the infection process of dermatophytosis.