Pseudomonas aeruginosa susceptibility, antibiogram and clinical interpretation, and antimicrobial prescribing behaviors for dogs with otitis in the Midwestern United States.

Pseudomonas aeruginosa (P. aeruginosa) can cause otitis in dogs that is nonresponsive to empirical therapy. This study evaluated P. aeruginosa isolates (N = 216) from canine ear swabs submitted to the Kansas State Veterinary Diagnostic Laboratory from 2018-2020 to create an antibiogram and minimum inhibitory concentration distributions using Clinical Laboratory Standards Institutes breakpoints. Multidrug resistance was defined as non-susceptibility to ≥1 drug from ≥3 antimicrobial classes. Submitting veterinarians (N = 83) were invited to complete a survey about antimicrobial use and otitis management. Susceptibility was higher for aminoglycosides [gentamicin (82%, 177/216) and amikacin (81%, 175/216)] than fluoroquinolones [marbofloxacin (67%, 145/216), enrofloxacin (32%, 70/216), and orbifloxacin (18%, 39/216)]. Most responding veterinarians (54%, 15/28) prescribe topical aminoglycosides as first-line therapy for canine otitis, but 71% (15/21) prescribe fluoroquinolones if rods are seen cytologically. Ceftazidime, imipenem, and piperacillin-tazobactam showed high susceptibility and are used rarely. Multidrug resistance was present in 13% (28/216) of isolates. Based on in vitro susceptibility, topical aminoglycosides might be more effective than fluoroquinolones for P. aeruginosa otitis, but efficacy studies are required. Susceptibility testing is encouraged for cases not responding to empirical therapy but has limitations because topical preparations have high concentrations and otic breakpoints are not available.