Essential Oils in the Control of Infections by Staphylococcus xylosus in Horses

• In vitro activity of nine essential oils against Staphylococcus xylosus was evaluated.
• The sauce thyme and oregano inhibited with an MIC ≤0.25% (v/v) all tested isolates (n = 27).
• The minimal bactericidal concentration for sauce thyme was 0.31% and 0.52% for oregano.
• These oils could be used in the control of S. xylosus infections.

The antimicrobial activity of nine essential oils (cinnamon, palmarosa, Indonesian and Madagascar cloves, niaouli, peppermint, oregano, rosemary, and sauce thyme) against Staphylococcus xylosus isolates obtained from the nasal mucosa of healthy and diseased horses has been valued. A total of 27 isolates with different resistance profile (susceptible, resistant to one antimicrobial class, resistant to ≥2 antimicrobial classes) were analyzed. An initial screening study was carried out to determine the antimicrobial activity of essential oils against 10 S. xylosus isolates, following the disk-diffusion method. Five essential oils with major inhibitory zone were selected, and the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) against the 27 isolates were performed by a broth microdilution method. All the essential oils, except rosemary (inhibitory zone diameter of 6 mm for 100% of isolates), showed antimicrobial activity against S. xylosus. The MIC and MBC values were obtained for cinnamon, clove, peppermint, oregano, and sauce thyme. Our results show that sauce thyme (0.07 ± 0.05% and 0.31 ± 0.39%, respectively) and oregano (0.12 ± 0.04% and 0.52 ± 0.42%, respectively) presented the lowest MIC and MBC average values. No significant differences were observed between the inhibitory activity and the resistance profile of the isolates. The sauce thyme and oregano could be used in the control of S. xylosus infection in horses. More studies are necessary to establish their clinical potential use, as well as their dose and application options.