Insights into Klebsiella pneumoniae carbapenem resistance—a two-year retrospective study from a Romanian tertiary care hospital

Introduction Antimicrobial resistance amongst Klebsiella pneumoniae isolates imposes a significant clinical and public health burden, requiring a large healthcare expense for the treatment of infections. The last decade has seen an incremental rise in antimicrobial resistance, not only toward carbapenems, but also last-resort antimicrobials, urging the need for collaboration between infectious diseases specialists and microbiology peers toward the development of novel therapeutic methods. This study aims to provide a two-year overview in carbapenem-resistant Klebsiella pneumoniae (CRKP) in an infectious diseases tertiary hospital in Romania, focusing on antimicrobial resistance patterns and carbapenemase distribution. Methods Clinical samples collected from patients admitted to the “Prof. Dr. Matei Bals” National Institute of Infectious Diseases in Bucharest, Romania, between 1st August 2023 and 31st July 2025 have undergone standard cultivation, bacterial identification and antimicrobial susceptibility testing according to standard laboratory protocol. All carbapenem-non-susceptible Klebsiella pneumoniae strains (meropenem minimum inhibitory concentration > 0.125 μg/mL) further underwent extended-spectrum beta-lactamase (ESBL) and carbapenemase production testing via phenotypical methods. Results A number of 340 non-duplicate, carbapenem-non-susceptible Klebsiella pneumoniae strains have been isolated from various clinical samples. The majority of them (> 90%) exhibited carbapenemase production: n = 164, 53.59% double NDM and OXA-48-type carbapenemase producers, followed by NDM ( n = 74, 24.18%), OXA-48-type ( n = 44, 14.38%), KPC ( n = 14, 5.56%) and NDM+KPC ( n = 7, 2.29%). In addition, 309 strains were deemed ESBL producers. In terms of antimicrobial resistance, more than > 90% of the strains exhibited resistance to fluoroquinolones, third generation cephalosporins, penicillins and monobactams, > 75% resistance to aminoglycosides and novel beta-lactam/beta-lactamase inhibitor combinations and > 70% resistance to colistin and imipenem-relebactam. Overall cefiderocol resistance was 32.05%. Upon classification, 25.00% ( n = 85) of isolates were multidrug-resistant (MDR), 56.47% ( n = 192) extensively drug-resistant (XDR) and 17.06% ( n = 58) were pandrug-resistant (PDR). Moreover, 54.17% ( n = 104) of XDR isolates were only susceptible to one antimicrobial drug. Conclusion Rates of resistance remain concerningly high amongst CRKP isolates, with double carbapenemase producers and XDR/PDR isolates dominating the landscape, implying the foreseeable need for updated means of approaching antimicrobial resistance, as last-resort antimicrobials become less effective through increasing resistance.