Klebsiella pneumoniae stands out as an opportunistic pathogen frequently associated with healthcare-related infections. It is classified as a critical priority by the WHO regarding antimicrobial resistance due to the production of extended-spectrum β-lactamases (ESBLs) and carbapenemases, which contribute to its dissemination and clinical impact. Considering its ubiquitous distribution and potential circulation among humans, animals, and natural environments, the objective of this study was to investigate K. pneumoniae strains producing ESBL and/or carbapenemases isolated from marine ecosystems in the municipality of Niterói/RJ, Brazil.

Seawater samples were collected from three beaches in Niterói. The isolated colonies were identified through mass spectrometry (MALDI-TOF MS). After screening K. pneumoniae strains under selective pressure, the disk diffusion test was performed to evaluate susceptibility to 12 β-lactam antibiotics. The production of ESBL and carbapenemases was confirmed through the double-disk synergy test (DDST) and the modified carbapenem inactivation method (mCIM), respectively. Subsequently, the detection of the genes blaCTX-m-1, blaCTX-m-2, blaCTX-m-8, and blaKPC was performed by Polymerase Chain Reaction (PCR).

Of the 298 K. pneumoniae strains identified, 34 (11.4%) were selected through screening for susceptibility testing. Non-susceptibility to ertapenem was observed in four (11.7%) strains, and to meropenem and imipenem in three (8.8%) strains each. Ceftriaxone showed the highest resistance rate (50.0%), followed by cefazolin (47.0%), cefepime (41.2%), and cefoxitin (38.2%). Resistance to ceftazidime and cefotaxime was 35.2% and 29.4%, respectively. The DDST was positive in 55% of the tested strains, with six strains positive for the blaCTX-m-1 gene and four for blaCTX-m-8. The mCIM was positive in 13% of the evaluated strains, with detection of the blaKPC gene in two of them.

The detection of ESBL- and carbapenemase-producing K. pneumoniae in the coastal region of Niterói/RJ, with the presence of clinically relevant resistance genes, suggests that these areas may be acting as reservoirs and potential sources for the dissemination of these genetic determinants, representing an emerging public health risk.