Antimicrobial activity of eleven essential oils against otitis-associated Staphylococci and Streptococci isolated from canine ears

Canine otitis externa is a common problem seen in small animal practice. It is caused by different factors and bacterial infections with Staphylococci or Streptococci can perpetuate this condition. Essential oils as natural plant products were successfully used for local treatment of canine otitis. Aim of this study was to analyse the antimicrobial in vitro activity of eleven in vivo compliant essential oils against Staphylococcus pseudintermedius (n=10) and Streptococcus canis (n=10). A microdilution of essential oils to determine the minimum inhibitory and bactericidal concentration (MIC and MBC) was performed. Staphylococcus pseudintermedius and Streptococcus canis were strongly inhibited by citronella (MIC: both 0.25%; MBC: 0.50% and 0.46%), thyme chemotype thymol (MIC both 0.50%; MBC: 1.00% and 0.50%), and oregano oil (MIC: 1.00% and 0.50%, MBC: 1.67% and 0.67%). Basil, tea tree, lavender and rosemary oil showed a moderate inhibitory effect against Staphylococcus pseudintermedius (MIC: 1.25% -2.50%; MBC: 2.50 -≥5.00) and a good inhibitory effect against Streptococcus canis (MIC: 0.50% – 1.25%; MBC: 1.00% – 1.67%). Bergamot, clary sage, lemon, and grapefruit oil showed no inhibitory effect in the analysed concentrations (≤5.00%). Generally, Streptococcus canis was more susceptible than Staphylococcus pseudintermedius. In conclusion, citronella, thyme, and oregano oil are first choice essential oils for local treatment of canine otitis externa. Ideally for therapy, an essential oil should be chosen depending on the result of the bacteriological examination and its in vitro activity, since individual bacteria show different susceptibility patterns ([Fig. 1]).

Fig. 1 Antimicrobial activity of essential oils against otitis-associated Staphylococcus pseudintermedius and Streptococcus canis

 

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Conflict of Interest

The authors declare no conflict of interest.

Publication History

Article published online:
16 November 2023