In vitro antimicrobial activity of miconazole and polymyxin B against canine meticillin-resistant Staphylococcus aureus and meticillin-resistant Staphylococcus pseudintermedius isolates

Abstract

Background- Meticillin-resistant Staphylococcus aureus (MRSA) and meticillin-resistant Staphylococcus pseudintermedius (MRSP) infections are increasingly reported in dogs, and these bacteria may be isolated from ear infections. Hypothesis/Objectives- The main aim of the present study was to investigate the in vitro antimicrobial activity of miconazole, polymyxinB and a combination of both against 24 canine MRSA and 50 canine MRSP isolates. The minimal inhibitory concentration (MIC) values of 12 other antimicrobial agents were also determined. Methods- All MIC values were determined according to a broth microdilution assay. Results- Acquired resistance was found to all tested agents, except for linezolid, miconazole and polymyxinB. The MIC values for miconazole and polymyxinB against MRSA were in the range of 4-8 and 8-64μg/mL, respectively, while the MIC values for miconazole and polymyxinB against MRSP were in the range of 1-2 and 0.25-4μg/mL, respectively. Using a combination of miconazole and polymyxinB, there was no evidence for enhanced in vitro activity of the combination (i.e. synergy) of both products. Nevertheless, MIC90 values of the combination of these antimicrobial agents and of a commercial product containing both agents were at least 1000 times lower than the concentration present in the commercial product. Conclusions and clinical importance- These results indicate that the topical use of a combination of miconazole and polymyxinB in a 43.5:1 ratio may have potential for the treatment of MRSA-mediated and MRSP-associated otitis externa in dogs. © 2012 The Authors. Veterinary Dermatology. © 2012 ESVD and ACVD.