In Vitro Antimicrobial Activity of Thymus vulgaris, Origanum vulgare, Satureja montana and Their Mixture against Clinical Isolates Responsible for Canine Otitis Externa

SIMPLE SUMMARY: Otitis externa of dogs is the inflammation of the external ear canal and may be acute or chronic, persistent or recurrent. Several bacterial species are involved in otitis externa and often Malassezia yeasts are simultaneously present. Otitis externa is often a severe problem in veterinary medicine because of the resistance of the involved pathogens to conventional drugs. Essential oils (EOs) could be promising products with which to treat these inflammations. EOs from Origanum vulgare, Satureja montana, and Thymus vulgaris seem to be active to the main bacterial species and M. pachydermatis cultured from the ears of dogs with otitis; moreover, a mixture of these three components seems to improve the antibacterial property. ABSTRACT: Otitis externa is a frequent inflammation among dogs, mainly caused by bacteria and yeasts that are often resistant to conventional drugs. The aim of the present study was to evaluate the in vitro antibacterial and antifungal activities of commercial essential oils (EOs) from Origanum vulgare, Satureja montana, and Thymus vulgaris, as well as a mixture of these three components, against 47 clinical bacterial strains (Staphylococcus sp., Streptococcus sp., Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Serratia marcescens) and 5 Malassezia pachydermatis strains, previously cultured from the ears of dogs affected by otitis externa. The tested Gram-positive bacteria were sensible to the analysed EOs with MICs ranging from 1.25% (v/v) to <0.0195% (v/v); Gram-negative isolates, mainly P. aeruginosa, were less sensitive with MICs from >10% (v/v) to 0.039% (v/v). M. pachydermatis isolates were sensitive to all EOs with MICs from 4.25% (v/v) to 2% (v/v). However, the mixture was active against all bacterial (except one P. aeruginosa strain) and fungal tested isolates. The three EOs and their mixture seem to be an interesting alternative for treating canine otitis externa when conventional antimicrobials are not active.