Detection of Extended‐Spectrum β‐Lactamases, Metallo‐β‐Lactamases, Antimicrobial Resistance Profiles, and Biofilm‐Forming Capacity in <i>Pseudomonas aeruginosa</i> Strains Recovered From Dogs With Otitis Externa in Italy

<i>Pseudomonas aeruginosa</i> is considered the second major causative agent of otitis externa in dogs, after <i>Staphylococcus pseudintermedius</i>. This study aimed to evaluate the antimicrobial resistance profiles and to detect the extended-spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL) genes in <i>Pseudomonas aeruginosa</i> (<i>P. aeruginosa</i>). Precisely, seventeen <i>P. aeruginosa</i> strains, recovered from auricular specimens of dogs affected by otitis externa, were identified by MALDI-TOF MS. Antimicrobial susceptibility testing was carried out against eleven clinically relevant antimicrobials using the Kirby Bauer disk diffusion method on Mueller Hinton agar plates. The PCR assay was performed to detect ESBL <i>bla</i> _{<i>CTX</i>-<i>M</i>} , <i>bla</i> _<i>TEM</i> , <i>bla</i> _<i>SHV</i> , <i>bla</i> _<i>PER</i> , and MBL <i>bla</i> _<i>IMP</i> , <i>bla</i> _{<i>OXA</i>-48}, <i>bla</i> _<i>VIM</i> , <i>bla</i> _<i>NDM</i> , <i>bla</i> _<i>GES</i> genes. The results showed that <i>P. aeruginosa</i> isolates had a phenotypic resistance value of 100% to ceftazidime, imipenem, and meropenem, followed by piperacillin-tazobactam, sulfamethoxazole-trimethoprim (94%), and aztreonam (88%). An alarming result was represented by the high prevalence of multidrug-resistant strains with 100% of the total isolates. The most common ESBL-genotype combination was <i>bla</i> _<i>PER</i> + <i>bla</i> _<i>SHV</i> (29.4%). Thirteen isolates (76.5%) carried together <i>bla</i> _<i>VIM</i> + <i>bla</i> _<i>GES</i> genes, which resulted to be the most common MBL-genotype combination. All the isolates harboring ESBL and MBL genes were biofilm producers, evaluated by the crystal violet-based assay and PCR. Precisely, 76.5% were strong biofilm producers, and 23.5% resulted in being moderate producers. No relationship was observed between strong or moderate biofilm producers and numerical variability of ESBL and MBL genes. This study revealed worrying antimicrobial resistance profiles of <i>P. aeruginosa-</i>associated canine otitis externa, considering also the zoonotic potential of this pathogen.