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

UNLABELLED: 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.