Multi-azole-resistant strain of Malassezia pachydermatis isolated from a canine Malassezia dermatitis

In the case presented here, we describe the isolation of an azole-resistant strain of M. pachydermatis from a canine Malassezia dermatitis. The isolate (NUBS18001) from this case exhibited a minimum inhibitory concentration (MIC) of 320 μg/ml to itraconazole (ITZ) by broth microdilution (BM) assay, >32 μg/ml to ITZ by E-test, and >32 μg/ml to KTZ by E-test. Synergistic effects between FK506 and ITZ in the azole-resistant strain was evaluated using the microdilution checker-board method. The ITZ-resistant strain exhibited MICs of 320 μg/mL of ITZ alone and 5 μg/ml of FK506 alone; the addition of FK506 attenuated the ITZ MIC to 2.5 μg/ml, yielding an ITZ FICI value of 0.507. This result suggested that the combination of ITZ and FK506 exerted an additive effect against the ITZ-resistant strain. To understand the other mechanism inferred to be present in our multi-azole-resistant strain, we sequenced the ERG11 gene from this isolate, and detected missense mutations (A412G and C905T) in the sequence of the ERG11 open reading frame (ORF). To the best of our knowledge, this work is the first report that a multi-azole-resistant M. pacydermatis strain contains mutations in ERG11.