Peer-reviewed veterinary case report
Miconazole resistance in yeast from dogs with ear infections
By Belcher, Cole M et al.·Published in Veterinary dermatology·2026·Department of Pathobiology, United States·View original on PubMed →
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Original publication title: Phylogenetic and Structural Analysis of Miconazole Susceptibility in Malassezia pachydermatis Isolates From Dogs With Otitis Externa.
- Species:
- dog
Plain-English summary
A group of 11 dogs with ear infections caused by yeast (Malassezia pachydermatis) were treated with miconazole, a common antifungal medication, but some did not improve. Researchers found that certain genetic changes in the yeast made it less susceptible to miconazole, indicating that resistance is becoming a problem. They noted that while some mutations did not affect how the yeast responded to the treatment, others did, suggesting that new antifungal options may be needed for resistant cases. It's important for pet owners to be aware of this issue and discuss alternative treatments with their veterinarian if their dog's ear infection isn't improving.
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Abstract
BACKGROUND: An increased number of dogs with unresolved yeast otitis externa (OE) after miconazole treatment was observed at a tertiary practice. HYPOTHESIS/OBJECTIVES: To evaluate miconazole susceptibility in Malassezia pachydermatis isolates from canine OE. ANIMALS: Eleven client-owned dogs (16 ears) with clinical and video otoscopic signs of OE and cytological evidence of yeast. MATERIALS AND METHODS: Yeast cultures were derived from ear swabs. PCR amplified portions of the internal transcribed spacer region (ITS), and partial sequences encoding the 18S rRNA small subunit (SSU), 26S rRNA large subunit (LSU), and actin (ACT1) loci for phylogenetic analysis, as well as the ERG11 gene that encodes lanosterol 14α-demethylase. Miconazole susceptibility was assessed by disk diffusion on Mueller-Hinton agar. Molecular modelling was used to evaluate the relationship between lanosterol 14α-demethylase amino acid substitutions and miconazole susceptibility. RESULTS: Isolates of M. pachydermatis from canine OE formed a three-clade phylogeny. Most ERG11 mutations predicted lanosterol 14α-demethylase substitutions that were clade-specific without an effect on miconazole susceptibility. Reduced susceptibility was associated with substitutions of amino acid A302, located in the lanosterol 14α-demethylase azole-binding site. Other altered amino acids were located elsewhere in the lanosterol 14α-demethylase protein without an apparent effect on miconazole binding. CONCLUSIONS AND CLINICAL RELEVANCE: Clinical isolates of M. pachydermatis with reduced miconazole susceptibility were easily found, suggesting that miconazole resistance is present in routine patients. Lanosterol 14α-demethylase interactions with longer-tailed azoles involve additional contacts beyond A302 suggesting these drugs will be more effective against miconazole-resistant strains. However, effective antifungal stewardship is needed to slow development of pan-azole resistance that would limit treatment options for dogs with M. pachydermatis-associated disease.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/41852310/