Kurtz, PedroDel Peloso, Pedro F.Pribul, Bruno RochaAlbuquerque, Arthur M.Antunes, Bianca B.P.Ramos, Grazielle ViannaBozza, Fernando A.2026-01-142026-01-142025-111664-302XPURE: 147373702PURE UUID: 634b0826-8a24-4e9a-a145-7befcd3487efScopus: 105023680635http://hdl.handle.net/10362/199003Publisher Copyright: Copyright © 2025 Kurtz, Del Peloso, Pribul, Albuquerque, Antunes, Ramos and Bozza.Background/Objectives: Carbapenemase-producing Enterobacterales and P. aeruginosa are critical threats to global public health, especially in high-burden regions such as Brazil. Imipenem-relebactam (IMR), a combination of a carbapenem with a β-lactamase inhibitor, is a promising treatment option against resistant Gram-negative bacteria. This study aimed to characterize phenotypic resistance and molecular mechanisms in clinical isolates from Brazilian hospitals and assess IMR activity. Methods: A prospective multicenter study was conducted across 12 hospitals in Rio de Janeiro. A total of 150 Enterobacterales and 100 P. aeruginosa isolates resistant to carbapenems were collected. Isolates were identified by MALDI-TOF and screened for carbapenemase genes (KPC, NDM, VIM, IMP, OXA-48) using PCR. Susceptibility to IMR was determined by broth microdilution following EUCAST guidelines. Next-generation sequencing (NGS) was performed on a subset of multidrug-resistant isolates. Results: IMR resistance was identified in 34.5% of K. pneumoniae and 74% of P. aeruginosa isolates. Among Enterobacterales, 21.1% of KPC-producers and 88.9% of OXA-48-producers were resistant to IMR. The bla_KPC gene was predominant, but NDM was increasingly detected. In P. aeruginosa, resistance was largely unrelated to carbapenemase production, implicating porin loss and efflux pumps. NGS revealed extensive co-resistance and multiple virulence genes in K. pneumoniae isolates. Conclusion: This study highlights the emergence of significant resistance to imipenem-relebactam in Brazil, driven by both enzymatic and non-enzymatic mechanisms. Ongoing molecular surveillance and tailored treatment strategies are essential to address the evolving threat of multidrug-resistant Gram-negative infections in endemic regions.280952engantimicrobial therapycarbapenemasegram-negativeimipenem-relebactammulti-drug resistantMicrobiologyMicrobiology (medical)SDG 3 - Good Health and Well-beingjournal article10.3389/fmicb.2025.1689777https://www.scopus.com/pages/publications/105023680635