Metabolic potentiation of antibiotic killing by L-arginine in drug-resistant <i>Edwardsiella tarda</i>

The role of metabolic state reprogramming in modulating antibiotic susceptibility has attracted growing interest as a promising strategy to combat antimicrobial resistance. Our study revealed that L-arginine potentiates chloramphenicol's bactericidal activity by at least two orders of magnitude against multidrug-resistant <i>Edwardsiella tarda</i> via the coordinated modulation of three interconnected metabolic pathways: the tricarboxylic acid cycle disruption, redox homeostasis alteration, and phenylalanine metabolic suppression. Mechanistically, L-arginine-mediated tricarboxylic acid cycle inhibition diminished NADH production and compromised proton motive force, thereby depleting cellular energy supply and impairing drug efflux capacity. Concurrently, L-arginine disturbed the bacterial redox balance, which normally provides antibiotic resistance, by both lowering total antioxidant capacity and raising reactive oxygen species production. Furthermore, L-arginine suppressed phenylalanine metabolism, whereas trans-cinnamate restored antioxidant defenses and proton motive force, diminishing antibiotic resistance. These findings expanded the understanding of metabolic modulation's role in combating antibiotic resistance and offered theoretical support for the development of new antimicrobial strategies.IMPORTANCEThe global crisis of antimicrobial resistance demands innovative strategies to revitalize existing antibiotics. Our work addresses this urgent need by demonstrating that L-arginine acts as a powerful potentiator of chloramphenicol, enhancing its bactericidal efficacy by over 100-fold against multidrug-resistant <i>Edwardsiella tarda</i>. More significantly, we elucidate a novel, dual-pathway mechanism: arginine concurrently disrupts the TCA cycle and phenylalanine metabolism, which collectively alter the cellular redox state and compromise the proton motive force. This study is the first to uncover this sophisticated metabolic interplay, providing not only a promising adjuvant strategy but also a new conceptual framework for combating resistant bacterial infections by targeting core metabolism. Our findings, therefore, hold substantial potential for both basic science and translational antimicrobial development.