MIC Distributions and CLSI-Categorized Resistance in Pseudomonas aeruginosa from Companion Animals in Poland: Evidence of Strong Meropenem–Ceftazidime Co-Non-Susceptibility

Pseudomonas aeruginosa is a clinically important opportunistic pathogen in dogs and cats, frequently associated with chronic infections and increasing antimicrobial resistance. In 2024, 111 P. aeruginosa isolates from 77 dogs and 34 cats were analyzed. Isolates originated from the external ear canal of animals with chronic otitis externa (66/111, 59.5%) and the nasal cavity of animals with chronic rhinitis (29/111, 26.1%), wounds (7/111, 6.3%), the conjunctival sac (5/111, 4.5%), and the skin (4/111, 3.6%). MICs for ciprofloxacin, meropenem, ceftazidime, aztreonam, piperacillin, piperacillin/tazobactam, and colistin were determined using a commercial microdilution panel and interpreted with CLSI M100 breakpoints for P. aeruginosa. Susceptibility was highest to piperacillin and piperacillin/tazobactam (both 90.1% susceptible and 7.2% resistant). Resistance was more frequent to ciprofloxacin (26.1%), meropenem (17.1%), and ceftazidime (16.2%). Colistin resistance (MIC ≥ 4 µg/mL) was detected in 6.3% of isolates. MDR (Magiorakos definition; non-susceptibility to ≥1 agent in ≥3 antimicrobial categories) was identified in 17/111 (15.3%) isolates. Meropenem non-susceptibility was strongly associated with ceftazidime non-susceptibility (25/111, 22.5%; OR 11.21; 95% CI 4.29–29.30; phi 0.51; p = 2.4 × 10−7). These findings provide baseline phenotypic surveillance data for P. aeruginosa from companion animals in Poland and highlight clinically relevant co-non-susceptibility patterns involving meropenem and ceftazidime.