Genomic Characterization of Carbapenem-Resistant Acinetobacter baumannii (OXA-23) and Klebsiella pneumoniae (KPC-2) Causing Hospital-Acquired Infections in Dogs

<b>Background/Objectives:</b> Antimicrobial resistance is a major global health threat. Among the most problematic pathogens are carbapenem-resistant <i>Acinetobacter baumannii</i> and <i>Klebsiella pneumoniae</i>, which are significant causes of mortality in humans, particularly in the context of nosocomial infections. In companion animals, these bacteria have been reported mainly as colonizers of healthy animals or, less frequently, in community-acquired infections. However, no confirmed cases of healthcare-associated infections caused by these species have been documented in this population. This study reports the first confirmed fatal cases of infection with carbapenem-resistant <i>A. baumannii</i> and KPC-producing <i>K. pneumoniae</i> in dogs. <b>Methods</b>: Three hospitalized dogs developed infections associated with distinct anatomical devices, including a venous catheter, an endotracheal tube, and a Penrose drain. Bacterial isolation followed by antimicrobial susceptibility testing identified carbapenem-resistant <i>A. baumannii</i> and <i>K. pneumoniae</i>. The isolates were subsequently subjected to additional antimicrobial resistance tests and whole-genome sequencing (WGS). <b>Results</b>: WGS confirmed the presence of the OXA-23 carbapenemase gene in both <i>A. baumannii</i> isolates and the KPC-2 carbapenemase gene was detected in the <i>K. pneumoniae</i> strain. All three strains exhibited resistance to multiple antimicrobial classes, including β-lactams (amoxicillin-clavulanic acid, ampicillin, cephalotin, piperacillin-tazobactam, cefoxitin, ceftiofur, cefotaxime, ertapenem, imipenem and meropenem), aminoglycosides (gentamicin, neomycin), tetracyclines (doxycycline, tetracycline and oxytetracycline), fluoroquinolones (ciprofloxacin, enrofloxacin), and folate pathway antagonists (trimethoprim-sulfamethoxazole). Multilocus sequence typing identified two high-risk clones: <i>K. pneumoniae</i> ST340 (CC258) and <i>A. baumannii</i> ST15 (CC15). Single nucleotide polymorphism analysis confirmed a high degree of genetic similarity between these isolates and strains previously associated with human infections in Brazil. <b>Conclusions</b>: These findings provide the first evidence of fatal, healthcare-associated infections caused by these multidrug-resistant pathogens in dogs and underscore the need to strengthen surveillance and infection control practices in veterinary hospitals. Furthermore, the results raise concerns about the potential of companion animals to act as reservoirs for multidrug-resistant organisms of public health relevance.