Background The increasing prevalence of antimicrobial resistance among bacteria in dogs with otitis externa has led to a need for novel therapeutic agents. Hypothesis/Objective To examine the antibacterial effects of manuka oil combined with ethylenediaminetetraacetic acid–tromethamine (Tris‐EDTA) against Gram‐negative bacteria isolates from dogs with otitis externa. Methods and materials A total of 53 clinical isolates including Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae ssp. pneumoniae and Proteus mirabilis. Antimicrobial susceptibility was determined using disk diffusion; the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of manuka essential oil, with or without Tris‐EDTA, were investigated. Results A total of 44 isolates were resistant to at least one antibiotic and 19 strains were multidrug‐resistant, with resistance to at least one agent in three or more antimicrobial classes. The MICs and MBCs of manuka oil alone were ≥1% (v/v) and ≥2% (v/v), respectively. There was no antimicrobial effect of Tris‐EDTA (1.125:0.3 mg/mL) without manuka oil. However, the combination of manuka oil with Tris‐EDTA significantly decreased the MICs (ranging from 0.06% to 0.5%, v/v; P < 0.001) and MBCs (ranging from 0.06% to 1%, v/v; P < 0.001). There also was no significant difference between multidrug‐resistant and nonresistant bacterial isolates in terms of the antimicrobial activity of manuka oil with Tris‐EDTA. Conclusions and clinical importance The study findings suggest that manuka oil, especially when combined with Tris‐EDTA, may be a promising alternative therapeutic option for Gram‐negative otic pathogens. Clinical studies are needed to assess potential for in vivo ototoxic effects and efficacy.

Background: Cold atmospheric microwave plasma (CAMP) is a promising therapeutic option for treating skin infections and wounds. Changes in biophysical skin parameters and the tolerability in dogs after applying CAMP is unknown.Objective: This study aimed to evaluate the in vivo effects of CAMP on skin biophysical parameters [hydration, transepidermal water loss (TEWL) and surface temperature] and tolerability in dogs.Animals: Twenty client-owned dogs with normal skin. Materials and methods:Cold atmospheric microwave plasma treatment was performed for 30 s and 1, 2 and 4 min, respectively, at different sites of normal canine skin in the inguinal area. Hydration, TEWL and surface temperature were measured five, three and three times, respectively, before and after CAMP application. After treatment, pain and adverse effects were evaluated using a modified Melbourne Pain Scale and the modified short form Glasgow Composite Measure Pain Scale (modified CMPS-SF). Results:Transepidermal water loss values significantly decreased with 4 min of treatment, and hydration decreased significantly with 2 min of treatment.Temperature increased significantly with increasing treatment time. For other parameters, no significant changes were observed. No significant pain response or adverse effects were observed in most dogs, aside from mild erythema in the treatment area after 4 min. Conclusion and clinical significance:Cold atmospheric microwave plasma treatment was well-tolerated and did not significantly change canine skin biophysical parameters. CAMP achieves basic recommendations for safe use and is a potential therapeutic option for various skin diseases in dogs.