A comprehensive review of the taxonomy, pathogenesis, and therapeutic challenges of Malassezia pachydermatis in companion animals.

Malassezia pachydermatis is a lipophilic yeast that forms part of the skin microbiota of dogs and cats, and can transform into an opportunistic pathogen when the microbial equilibrium is disrupted. It is most commonly implicated in cases of otitis externa and dermatitis in dogs, and is increasingly isolated from cats as well, particularly in instances of otitis externa. The rising number of infections reported in recent years underscores the growing significance of this microorganism in veterinary medicine. Despite its clinical relevance, standardized methods for assessing the antifungal susceptibility of M. pachydermatis are still lacking. Existing studies vary in the culture used, incubation conditions, and interpretation of minimum inhibitory concentration (MIC) values, which complicates the comparison of results and the evaluation of the true extent of antifungal resistance. Of particular concern is the increasing resistance to azoles, which remain the cornerstone of therapy for Malassezia-associated infections. Due to the limitations in efficacy and safety of conventional antifungal drugs, natural compounds with antifungal activity, including essential oils, are receiving increasing attention. These oils are mixtures of volatile plant metabolites with a broad spectrum of biological activity, including antibacterial, anti-inflammatory, and antifungal properties. Selected essential oils, such as oregano and thyme oils, have been shown to exhibit significant activity against yeasts of the genus Malassezia. Their potential therapeutic application represents a promising research direction, particularly in the context of increasing resistance to conventional antifungal agents.