Phenotypic profile and molecular mechanism of resistance in carbapenemase-producing Enterobacterales and Pseudomonas aeruginosa isolates from Brazilian Hospitals: implications for the introduction of Imipenem-Relebactam

Pedro Kurtz^1,2*Pedro F Del Peloso²Bruno Rocha Pribul³Arthur Albuquerque⁴Bianca B P Antunes⁵Grazielle Vianna Ramos²Fernando A Bozza^2,3*

• ¹Instituto Estadual do Cérebro Paulo Niemeyer (IECPN), Rio de Janeiro, Brazil
• ²Instituto D'Or de Pesquisa e Ensino, Rio de Janeiro, Brazil
• ³Fundacao Oswaldo Cruz, Rio de Janeiro, Brazil
• ⁴Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
• ⁵Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Brazil

Abstract Background/Objectives: Carbapenemase-producing Enterobacterales and Pseudomonas 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 Klebsiella 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. Conclusions: 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.