Background and Aim: The production of beta-lactamase enzymes, such as extended-spectrum beta-lactamase (ESBL), adenosine-monophosphate-cyclic (AmpC), and Klebsiella pneumoniae carbapenemase (KPC), is one of the most important mechanisms of bacterial resistance to antimicrobials. Gram-negative bacteria show significant resistance due to various intrinsic and acquired factors. These intrinsic factors include low permeability of the outer membrane, various efflux systems, and the production of beta-lactamases, while acquired factors include chromosomal mutation and acquisition of resistance genes by horizontal transfer. Mobile elements such as plasmids, integrative conjugative elements, mobilizable islands, or transposable elements are involved in horizontal transfer. At present, the Gram-negative pathogens of most concern are Acinetobacter baumannii, Pseudomonas aeruginosa, and those belonging to the Enterobacteriaceae family (e.g., Escherichia coli, K. pneumoniae, and Proteus mirabilis). This study aimed to evaluate the profile of antimicrobial resistance and the production of the enzymes ESBL, AmpC, and KPC, in 21 gram-negative bacteria isolated from domestic animals treated at the University Veterinary Hospital (HVU) of the Federal University of Western Bahia (UFOB).

Materials and Methods: The biological samples (21) were inoculated to brain heart infusion broth, blood agar, and MacConkey agar and incubated for 24-72 h at 37°C. Gram staining and identification through biochemical tests and matrix-associated laser desorption/ionization time-of-flight mass spectrometry were conducted. To evaluate the antimicrobial resistance profile, the disk diffusion method was used, and 25 antibiotics were employed. For the detection of ESBL, the disk approximation method was applied using chromogenic agar. The presence of KPC was observed using chromogenic agar and the Hodge test. For AmpC evaluation, the disk approximation method was used.

Results: The most isolated agent was E. coli (66.66%, 14/21), followed by K. pneumoniae and P. mirabilis (both 14.29%, 3/21), and then Pasteurella spp. (4.76%, 1/21). The bacterial isolates showed high levels of resistance against clindamycin, penicillin, imipenem, polymyxin, cefoxitin, gentamycin, cefotaxime, ceftazidime, cephalothin, ceftriaxone, ciprofloxacin, trimethoprim/sulfamethoxazole, chloramphenicol, and tetracycline. The best effectiveness rates were observed for cefepime, streptomycin, amoxicillin-clavulanate, aztreonam, nalidixic acid, tobramycin, levofloxacin, amikacin, and meropenem. All biological isolates showed multiple resistance to at least three of the antibiotics tested (3/25), and some showed resistance to 24 of the antibiotics tested (24/25). Among the 21 pathogens analyzed, 8 were ESBL producers (38.09%); of these, 6 were identified as E. coli (28.57%), and 2 were identified as K. pneumoniae (9.52%). Two strains of K. pneumoniae produced both ESBL and KPC. None of the isolates were producers of AmpC.

Conclusion: The results found in the present work raise concern about the level of antimicrobial resistance among pathogens isolated from domestic animals in Brazil. The results highlight the need for the development and implementation of anti-resistance strategies to avoid the dissemination of multiresistant pathogens, including the prudent use of antimicrobials and the implementation of bacterial culture, antimicrobial sensitivity, and phenotypic tests for the detection of beta-lactamase enzymes in bacteria isolated from animals.

Keywords: antimicrobial resistance, extended-spectrum beta-lactamase, Klebsiella pneumoniae carbapenemase, phenotypic tests.