In vitro susceptibility of Malassezia furfur against azole compounds

The minimum inhibitory concentrations (MICs) for 30 isolates of Malassezia furfur of four azole compounds - bifonazole, climbazole, clotrimazole and ketoconazole were determined as these substances are used in the topical therapy of M. furfur-associated skin conditions. M. furfur is a lipophilic fungus with complex growth requirements; the MICs were measured in a microdilution test system in modified Leeming-Notman medium by a colorimetric read-out with alamarBlue(TM). The MICs of bifonazole ranged between <9.06 and 1 mu g ml(-1) with an empirical median of 0.06 mu g ml(-1), for climbazole the MICs were < 0.06 to 0.5 mu g ml(-1) (median < 0.06 mu g ml(-1)), for clotrimazole < 0.06 to 8 mu g ml(-1) (median 1 mu g ml(-1)), and for ketoconazole <0.06 to 0.12 mu g ml(-1) (median < 0.06 mu g ml(-1)). Climbazole and ketoconazole showed similar in vitro activity against M. furfur, with bifonazole having slightly lower, and clotrimazole the lowest in vitro activity. These findings may be explained by the extremely low water solubility of the last two compounds; the results have yet to be correlated with the in vivo efficacy of these substances.