Adaptation of Microsporum gypseum to ketoconazole

The mycelium of the strain MG-155 of the dermatophyte Microsporum gypseum was repeatedly cultivated in three subinhibitory concentrations of ketoconazole: 1, 2, and 6 micrograms/ml. The adaptability of the fungus to this antifungal drug was estimated on the basis of the sensitivity of spores and the sensitivity of the mycelium. In the first phase, the mycelium grew on the medium with ketoconazole in consequence to the physiological adaptation (without the change of genome). In the following phase of the adaptation training, there occurred a manifestation of resistant mutants. After twenty-eight transfers, only a slight increase of resistance was found (resistance level = 2), however, this resistance was of a constant character. Basing on the data of ergosterol amount, there is discussed the biochemical mechanism of the described changes in the sensitivity of the fungus to ketoconazole.