Antibacterial and Antifungal Activity of Essential Oils against Pathogens Responsible for Otitis Externa in Dogs and Cats

Background: Essential oils (EOs) are recommended by some veterinarians to treat otitis externa in pets, but data about their efficacy in scientific literature are very scant. Methods: Nine commercial EOs, from roman chamomile (Anthemis nobilis L.), star anise (Illicium verum), lavender (Lavandula hybrida), litsea (Litsea cubeba (Lour.) Pers.), basil (Ocimum basilicum L.), oregano (Origanum vulgare L. subsp. hirticum), rosemary (Rosmarinus officinalis L.), clary sage (Salvia sclarea L.), and thyme (Thymus vulgaris L.) were tested against bacterial and fungal pathogens previously isolated from dogs and cats with otitis externa. In particular, the analyses were carried out against Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus pseudointermedius, Aspergillus niger, Aspergillus fumigatus, Aspergillus terreus, Candida albicans, Candida tropicalis, Trichosporon sp., and Rhodotorula sp. Results: O. vulgare and S. sclarea showed superior antibacterial activity, even if not against all the strains. Trichosporon sp., C. albicans, and A. terreus were insensitive to most Eos, while other yeasts and molds showed different degrees of sensitivity. In particular, most fungi were inhibited by O. vulgare and R. officinalis. Conclusions: The obtained results suggest that some EOs could be included in treatment as an alternative therapeutic option in bacterial otitis complicated by fungi, in association with conventional drugs.