The parasitic phase of the fungi of chromoblastomycosis: development of sclerotic cells in vitro and in vivo.

Like many other fungi pathogenic to man, the fungi that cause chromoblastomycosis are dimorphic, i.e., they have an extensive, fila? mentous, conidia-producing mycelium in the saprophytic phase, and in the parasitic phase, a much reduced thallus?small aggregates of spheri? cal, brownish-yellow cells with thick, deeply-pigmented walls, dividing by septation rather than budding (Figs. 1, 2). These structures, called sclerotic cells because of their thick walls, are believed to be highly resistant. Actual determinations of their vulnerability, however, are lacking and although their morphology is known in detail (7), the physiology of sclerotic cells is obscure, largely because this phase has not yet been elicited in artificial media, and is usually not obtainable in sufficient quantity from infected tissues. In other dimorphic fungi, artificial induction of the parasitic phase has permitted some insight into the determinants of dimorphism (3, 8, 9, 12, 15, 16, 18). To understand the adaptation of a fungus to parasitism it is necessary to identify the factors governing the appearance of the parasitic type of morphology. Success here might aid in the devel? opment of a rational therapy for the disease. Methods were sought, therefore, to induce the parasitic phase regu? larly and in quantity. The studies were conducted both in vitro and in vivo.