In vitro and in vivo enhancement of colistin activity against Escherichia coli strains by macelignan

Colistin remains a last-line antibiotic against multidrug-resistant Gram-negative pathogens, but its clinical utility is limited by nephrotoxicity and emerging resistance. This study identifies macelignan, a natural lignan from nutmeg, as a potent synergist that enhances colistin activity against Escherichia coli ( E. coli ) through a novel metabolic disruption mechanism. In vitro , macelignan reduced the colistin minimum inhibitory concentration (MIC) by approximately 100-fold, with the combination (8 µg/mL macelignan + 0.008 µg/mL colistin) achieving complete bacterial eradication within 4 h. In vivo , combination therapy significantly reduced bacterial burden in a mouse thigh infection model ( P < 0.05). Mechanistic studies revealed that macelignan disrupts bacterial energy metabolism by inhibiting the citric acid cycle, leading to ATP depletion. This energy compromise impairs the bacterial capacity to repair colistin-induced membrane damage, exacerbating membrane disruption and accelerating bacterial death. These findings establish macelignan as a promising adjuvant for colistin-based therapy and elucidate a dual “internal and external pincer” mechanism that could inform future antibiotic combination strategies. IMPORTANCE The continued efficacy of colistin, a last-line antibiotic against multidrug-resistant Gram-negative pathogens, is increasingly threatened by dose-limiting nephrotoxicity and the global spread of resistance determinants. This study introduces macelignan—a naturally occurring lignan from nutmeg—as a highly effective colistin adjuvant that operates through a previously unrecognized mechanism centered on metabolic disruption. By targeting the bacterial citric acid cycle, macelignan depletes intracellular ATP, thereby crippling the energy-dependent machinery required for membrane repair following colistin-induced damage. This dual “internal and external pincer” strategy not only dramatically reduces the colistin concentration needed for bactericidal activity but also significantly lowers bacterial burden in vivo . These findings provide a mechanistic framework for developing metabolism-targeting adjuvants to revitalize last-resort antibiotics and expand the therapeutic arsenal against recalcitrant Gram-negative infections.