The effect of ketoconazole and itraconazole on the filamentous form of Pityrosporum ovale.

The effect of ketoconazole and itraconazole on the filamentous form of Pityrosporum ovale in vitro was studied. In a recently developed model, using human stratum corneum in vitro, P. ovale transformed into the filamentous form in 25-30% of the cells. Ketoconazole and itraconazole in concentrations of 0.01, 0.1 and 1 microgram/ml were incubated together with P. ovale cells on human stratum corneum pieces placed on a lipid-enriched culture medium. Both agents effectively blocked the production of hyphae. From the low concentration onwards, the changes consisted of a diminishing transformation into hyphae. With transmission electron microscopy, the interior of many cells was often in an advanced stage of necrosis. Exposure to 1 microgram/ml itraconazole causes a disorganization of the internal organelles in 83% of the cells. This model for the production of hyphae of P. ovale in vitro proved very valuable in screening the activity of antimycotic agents against the filamentous form of this yeast.