Antimicrobial Susceptibility and Fluoroquinolone Resistance Patterns of Pseudomonas aeruginosa Isolated from Canine Otitis Externa in Romania

<b>Background/Objectives:</b> Canine otitis externa (OE) is frequently complicated by <i>Pseudomonas aeruginosa</i> (<i>P. aeruginosa</i>) infections, which are often associated with treatment failure due to intrinsic and acquired antimicrobial resistance. This study aimed to assess the prevalence and antimicrobial susceptibility of <i>P. aeruginosa</i> isolates from dogs with OE in Timiș County, Romania, with a focus on aminoglycosides and fluoroquinolones, to provide region-specific, clinically relevant data and address potential public health implications. <b>Methods:</b> Exudate samples were collected from 435 dogs diagnosed with OE across multiple veterinary clinics between 2022 and 2025. <i>P. aeruginosa</i> isolates were identified using standard culture methods, and antimicrobial susceptibility was determined using the VITEK^® 2 Compact system according to CLSI VET01, Fifth Edition (2018) guidelines. Tested antibiotics included amikacin, gentamicin, enrofloxacin, marbofloxacin, and pradofloxacin. Resistance profiles were analyzed at both the individual antibiotic and class levels. <b>Results:</b><i>P. aeruginosa</i> was isolated in 14.0% (61/435) of dogs. All isolates were susceptible to amikacin and gentamicin, whereas resistance to enrofloxacin and marbofloxacin was 27.9%, and pradofloxacin resistance reached 63.9%. A total of 24.6% of isolates were susceptible to all tested antibiotics. The most frequent multidrug-resistant combination among fluoroquinolones was ENR (R) + MAR (R) + PRA (R), observed in 23.0% of isolates. <b>Conclusions:</b> This study provides recent, region-specific data on <i>P. aeruginosa</i> prevalence and antimicrobial susceptibility in canine OE, offering clinically relevant insights into aminoglycoside and fluoroquinolone resistance. The findings highlight the potential public health significance of resistant <i>P. aeruginosa</i> strains at the human-animal interface and underscore the importance of antimicrobial stewardship in veterinary practice.