Evaluation of In Vitro Synergistic Interaction of Miconazole and Polymyxin B Against Clinical Strains of Malassezia pachydermatis

Malassezia pachydermatis is a yeast that is frequently involved as a secondary/perpetuating factor in canine otitis externa, along with numerous species of bacteria. As a result, otitis is generally treated with topical therapies using combinations of antifungal, antimicrobial and anti-inflammatory agents. The evaluation of the combined effect of drugs included in commercially available products is therefore important. In vitro synergy of polymyxin B and miconazole has been demonstrated against one strain type of M. pachydermatis. This study was aimed at investigating the in vitro interactions of these two agents against five clinical strains of this yeast. A chequerboard broth microdilution method was employed. We observed a synergistic action against all strains tested (fractional inhibitory concentration index comprised between 0.2 and 0.4). Our results indicate a strong therapeutic value for the association of these antimicrobial agents in the treatment of canine otitis externa caused by M. pachydermatis.