Antimicrobial effect of Chamacyparis obtusa and Thuja orientalis essential oils on Staphylococcus pseudintermedius isolated from canine skin and ears

Abstract

Staphylococcus pseudintermedius is the most commonly isolated opportunistic pathogen from skin and ear in dogs. The prevalence of methicillin-resistant or multi-drug resistant S. pseudintermedius is increasing. This has resulted in limited selection of antibiotics, which has become an important therapeutic challenge for veterinarians. The aim of this study is to evaluate the in vitro antimicrobial effect of Chamaecyparis obtusa and Thuja orientalis essential oils against bacteria and biofilm produced by S. pseudintermedius. Antimicrobial effect of two essential oils was assessed using 30 isolates of S. psuedintermedius form dogs with pyoderma and otitis externa. To evaluate the antimicrobial effect on bacteria, minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were measured and the results were compared to those of cephalexin. The MICs and MBCs of cephalexin were determined in the range of 2~256 ㎍/ml and 64~>256 ㎍/ml, respectively. The MICs of both essential oils were confirmed in the range of 2-4~2-5 % (v/v) and the MBCs were confirmed in the range of 2-1~2-4 % (v/v) and 2-2 ~2-4 % (v/v) for C. obtusa and T. orientalis, respectively. Although 70% of isolates are resistant to cephalexin, the MICs and MBCs of both essential oils were determined in constant range on all isolates including cephlexin resistant isolates. To evaluate the antimicrobial effect on established biofilm, biofilm inhibitory concentrations (BICs) and biofilm eradication concentrations (BECs) were determined. BICs of both essential oils were identified in the range of twofold~sixfold of MICs, %, v/v). BECs of C. obtusa and T. orientalis were identified in the range of fourfold~ninefold of MICs (%, v/v) and twofold~ninefold of MIC (%, v/v), respectively. Also, significant dose-dependent decrement of biofilm formation by both essential oils was determined by colorimetric microtiter assay for most isolates when comparing with the positive controls. This study demonstrates a significant in vitro antimicrobial effect of both essential oils on bacteria as well as biofilm produced by S. pseudintermedius. These results suggest the potential value of essential oils of C. obtusa and T. orientalis as alternative treatment options for skin and ear infections by S. pseudintermedius.