A Macromolecule npEt20 Exerts Broad-Spectrum Synergistic Effects With Meropenem Against Multidrug-Resistant Gram-Negative Pathogens

Background: The widespread emergence of multidrug-resistant (MDR) Gram-negative bacteria severely compromises the clinical efficacy of carbapenem antibiotics, leading to refractory nosocomial infections. Novel antibacterial agents that can reverse carbapenem resistance are urgently needed. Herein, this study aimed to evaluate the antibacterial activity of copolymer npEt20 and its synergistic effect with meropenem against clinical carbapenem-resistant isolates, and verify its potential as a meropenem adjuvant.Methods: The antibacterial activity and underlying mechanism of npEt20 against clinically isolated carbapenem-resistant strains, including Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa, were systematically characterized. Synergistic bactericidal effects of the npEt20-meropenem combination were assessed both in vitro and in vivo.Results: The npEt20 copolymer exhibited intrinsic broad-spectrum bactericidal activity against all three tested carbapenem-resistant isolates. Biofilm inhibition assays revealed that npEt20 significantly reduces mature biofilm biomass across all three pathogens in a concentration-dependent manner. Mechanistic studies demonstrated that npEt20 disrupted bacterial outer membrane integrity by increasing membrane permeability and inducing intracellular nucleic acid leakage. Repeated treatment with npEt20 could not induce detectable resistance phenotypes. Moreover, both in vitro and in vivo experiments demonstrated that npEt20 exhibited broad-spectrum synergistic performance and effectively reversed meropenem resistance in all three tested carbapenem-resistant pathogens.Conclusion: This work demonstrates that npEt20 acts as a broad-spectrum adjuvant capable of restoring meropenem activity against carbapenem-resistant A. baumannii, K. pneumoniae and P. aeruginosa in vitro and in a mouse infection model, which provides a promising preclinical strategy that requires further clinical validation for treating refractory carbapenem-resistant Gram-negative infections.