Compound amino acid synergizes ceftazidime-avibactam to eradicate extracellular and facultative intracellular MDR pathogens

With the rise in antibiotic-resistant infections, enhancing the efficacy of currently available antibiotics is crucial to address this crisis. In this study, we demonstrate that the clinically approved amino acid formulation 18AA (18 amino acids) synergistically enhances ceftazidime-avibactam (CZA) efficacy against extracellular and intracellular multidrug-resistant (MDR) pathogens, including carbapenem-resistant (CR) strains. The CZA+18AA combination eliminated CR Escherichia coli (CR-ECO) and MDR Edwardsiella tarda . Synergy was consistently demonstrated across all 10 tested clinical isolates, including CR-ECO, MDR-ECO, MDR E . tarda , and other CR pathogens, and validated in animal infection models. Mechanistically, 18AA promotes inosine biosynthesis, activating CusS/CusR-CusC regulatory pathways to increase antibiotic influx. This enhanced drug uptake overcomes resistance mechanisms mediated by efflux pumps and β-lactamases. Notably, these inosine-activated pathways were identified as previously unknown resistant mechanisms in antibiotic-sensitive bacterial mutants. Our findings establish nutritional adjuvants as clinically translatable tools to potentiate existing antibiotics against intractable MDR/CR infections through targeted metabolic modulation. • 18AA synergizes with ceftazidime-avibactam against multidrug-resistant pathogens • The combination eliminates clinically resistant isolates and is effective in vivo • 18AA enhances antibiotic influx through inosine and PMF • Inosine-CusS/R-CusC axis is a druggable target against resistant infections This study demonstrates that the FDA-approved drug 18AA potently resensitizes multidrug-resistant pathogens to ceftazidime-avibactam. It achieves this by activating two bacterial pathways, the inosine-CusS/R-CusC axis and the proton motive force, to promote antibiotic influx, offering a readily translatable strategy against formidable infections.