In vitro susceptibilities of human and wild-type isolates of Basidiobolus and Conidiobolus species

The in vitro activities of amphotericin B, miconazole, ketoconazole, 5-fluorocytosine, and potassium iodide (KI) were studied on human and wild-type isolates of Basidiobolus and Conidiobolus species. Of the antifungal agents tested, the imidazole derivatives, especially ketoconazole, were the most active against the agents of entomophthoromycosis. Transmission electron microscopy showed severe morphological alteration of Basidiobolus sp. exposed to 0.78 micrograms of ketoconazole per ml. The MIC and minimal fungicidal concentration of ketoconazole was often lowered in the presence of 10% fetal calf serum or antibiotic medium no. 3. Half of the Basidiobolus isolates and all Conidiobolus isolates were inhibited by amphotericin B at 0.39 micrograms/ml. None of the strains tested were inhibited or killed at maximum concentrations of 5-fluorocytosine and KI. The in vitro resistance of these fungi to KI at high concentrations suggests that the reported favorable treatment with KI may not be due to its direct effect on these fungi but rather to other, undefined factors in combination with KI. These data suggest that ketoconazole may be of use in the treatment of entomophthoromycosis, particularly in cases which are not responsive to KI.