In the face of increasing antimicrobial resistance, in 2017 the World Health Organization listed priority bacteria for prevention and treatment. Among these are carbapenem-resistant Enterobacterales, with Klebsiella pneumoniae being the main representative. This study aims to describe the evolution of carbapenem resistance and the resistance phenotypes of K. pneumoniae isolated in blood cultures.

Retrospective cross-sectional study with data from blood cultures positive for K. pneumoniae from a tertiary hospital between 2014 and 2024. Susceptibility to meropenem was evaluated according to the breakpoints proposed by CLSI (until 2020) or BrCAST (from 2021) for disk diffusion analysis (or gradient strip when resistance to meropenem was detected), and carbapenemase production was evaluated by phenotypic tests. Blood cultures from the same patient with identical resistance profiles during the same hospitalization were excluded. The outcomes evaluated were the proportion of susceptibility to meropenem, the proportion of carbapenem-resistant K. pneumoniae by carbapenemase production, and the proportion of enzymatic resistance mechanisms detected.

From 2014 to 2024, 1559 blood cultures with growth of K. pneumoniae were identified in 726 different patients. The overall meropenem resistance rate was 27.3% (426). From 2014 to 2017, meropenem resistance occurred in 9.2% of isolates (37/402); in 2018 it increased to 24% (23/96); and from 2019 to 2024 it remained at 34.5% (366/1061). Almost all (95% – 403/426) of the meropenem-resistant isolates produced carbapenemases. Among these resistant isolates, the production of serine β-lactamases (SBL) remained around 95.3% (384/403). The first isolates producing metallo-β-lactamases (MBL) were identified in 2019, with an increasing prevalence in recent years, reaching 57% (30/52) of isolates in 2024. Co-producing K. pneumoniae (SBL and MBL) were identified from 2021 and have also increased in proportion in recent years, reaching 44% (23/52) in 2024.

The increasing carbapenem resistance in K. pneumoniae isolates is concerning. The rising prevalence of MBL-producing K. pneumoniae impacts the choice of new antimicrobials available in Brazil, such as ceftazidime-avibactam, which lacks activity against this phenotype.