Lemongrass essential oil enhances antibacterial activity of cephalexin against Staphylococcus pseudintermedius isolated from dogs with superficial pyoderma

Superficial pyoderma in pets caused by Staphylococcus pseudintermedius is a common disease in veterinary medicine. Lemongrass essential oil has potent antibacterial effects, but studies of synergism of lemongrass essential oil with antibiotics are limited. This study examined the synergy of lemongrass essential oil with cephalexin against 7 S. pseudintermedius isolates obtained from dogs with superficial pyoderma by the checkerboard method and timekill test. All isolates tested were sensitive to methicillin, and the MICs of cephalexin and lemongrass essential oil ranged from 1-4 and 780-1560 mu g/ml, respectively. The checkerboard assay indicated that lemongrass essential oil had a partial synergistic effect with cephalexin; the concentration of cephalexin and lemongrass essential oil required to inhibit bacterial growth was reduced by 2-4 times. Time-kill assay revealed that the effects of cephalexin were time-dependent while the effects of lemongrass essential oil depended on both concentration and time. The main components of lemongrass essential oil identified by GC-MS were trans-citral (45.32% of total peak area) and cis-citral (35.43% of total peak area). The results of this study show that lemongrass essential oil had the potential to be used in combination with cephalexin for the control of superficial pyoderma in dogs caused by S. pseudintermedius.