Intestinal Colonization by Carbapenem-Resistant Gram-Negative Bacteria Harboring Carbapenemase and/or AmpC β-Lactamase Genes in Hospitalized Dogs and Cats in Brazil

Background/Objectives: Hospitalized companion animals may act as reservoirs of multidrug-resistant (MDR) Gram-negative bacteria and contribute to the dissemination of clinically important antimicrobial resistance genes. This study investigated gastrointestinal colonization by carbapenem-resistant Gram-negative bacteria harboring carbapenemase and/or AmpC β-lactamase genes in dogs and cats admitted to a Brazilian veterinary teaching hospital. Methods: Rectal swabs were collected from 106 animals at admission and discharge. Isolates were identified by biochemical methods and MALDI-TOF, screened by multiplex PCR for carbapenemase and AmpC β-lactamase genes, and characterized by antimicrobial susceptibility testing. Results: Fourteen (13.2%) animals were colonized, including animals colonized at admission, those in which colonization was detected only at discharge, and those remaining colonized throughout hospitalization, yielding 18 Gram-negative isolates from five bacterial species. blaNDM predominated (61.1%), followed by blaKPC, blaOXA-48-like, and blaSPM (16.7% each). PCR-based detection indicated the co-occurrence of carbapenemase and AmpC β-lactamase gene families in 66.7% of isolates, including uncommon combinations such as blaKPC + blaSPM and blaOXA-48-like + blaPER + blaEBC in Pseudomonas aeruginosa, without sequence-level confirmation. All isolates were MDR. Conclusions: Hospitalized companion animals may serve as reservoirs of clinically important MDR Gram-negative bacteria carrying carbapenemase and β-lactamase AmpC genes. These findings highlight the role of veterinary hospitals in the epidemiology of antimicrobial resistance and reinforce the need for molecular surveillance, antimicrobial stewardship, and infection prevention within a One Health framework.