In vitro efficacy of the essential oil from Leptospermum scoparium (manuka) on antimicrobial susceptibility and biofilm formation in Staphylococcus pseudintermedius isolates from dogs

Background Staphylococcus pseudintermedius is a common pathogen of skin and ear infections in dogs. The widespread and rapid emergence of meticillin‐resistant S. pseudintermedius (MRSP) has created therapeutic challenges in veterinary medicine and the need for alternative treatments. Hypothesis/Objectives We aimed to evaluate the in vitro antimicrobial activity of the essential oil manuka (Leptospermum scoparium) against S. pseudintermedius. Methods This study was performed using S. pseudintermedius strains isolated from dogs with skin and ear infections collected throughout Korea between 2009 and 2011. The in vitro antimicrobial activity of manuka oil against 39 MRSP and 11 meticillin‐susceptible S. pseudintermedius (MSSP) strains was analysed by measuring minimal inhibitory concentrations (MICs) using the agar dilution method and biofilm inhibition activity as assessed by the colorimetric microtitre plate assay. Results Our results indicated that manuka oil had excellent activity against all bacterial isolates. The MICs for MRSP and MSSP to manuka oil were in the range of 2−9 to 2−6 and 2−9 to 2−7% (v/v), respectively. Manuka oil was a potent inhibitor of S. pseudintermedius biofilm formation, and the majority of bacteria decreased by >50%. No significant differences were observed in the MICs or biofilm formation between the MRSP and MSSP strains. Conclusions and clinical importance These results suggest that manuka oil has the potential to be a useful therapeutic option for treating superficial infections caused by MRSP and MSSP; further clinical investigations are required. Résumé Contexte Staphylococcus pseudintermedius est un pathogène fréquent des infections cutanées et auriculaires chez le chien. L'émergence rapide et la dissémination de S. pseudintermedius résistant à la méticilline (MRSP) constituent des défis thérapeutiques en médecine vétérinaire et le besoin de nouveaux traitements. Hypothèses/Objectifs Nous voulons évaluer l'activité antimicrobienne in vitro de l'huile essentielle de manuka (Leptospermum scoparium) contre S. pseudintermedius. Méthodes Cette étude a été réalisée avec des souches de S. pseudintermedius prélevées sur des chiens atteints d'infections cutanées et auriculaires en Corée entre 2009 et 2011. L'activité antimicrobienne in vitro de l'huile de manuka contre 39 souches de MRSP et 11 souches de S. pseudintermedius sensibles à la méticilline (MSSP) a été analysée par la mesure des concentrations minimales inhibitrices (CMI)