Inhibition of Cronobacter sakazakii by Apigenin and the Antibacterial Mechanism

Cronobacter sakazakii is a significant foodborne pathogen commonly associated with dairy products, causing severe infections with high mortality rates, particularly in neonates and immunocompromised adults. In this study, we demonstrated that apigenin exhibits potent antibacterial activity against C. sakazakii, with a minimum inhibitory concentration (MIC) of 160 mg/L. Propidium iodide staining indicated that apigenin at sub-MIC and MIC concentrations had negligible effects on bacterial membrane integrity; only a 4.9% increase in membrane permeability was observed at 2 MIC, suggesting that membrane damage is not the primary antibacterial mechanism. Further analysis revealed that apigenin treatment significantly reduced Adenosine triphosphate (ATP) levels within 2 h without altering growth kinetics or membrane integrity, indicating that ATP reduction resulted from metabolic disruption rather than cell death. Targeted metabolomics analysis revealed distinct separation in metabolic profiles between apigenin-treated and control groups, identifying 19 differential metabolites enriched in multiple pathways, with the citric acid (TCA) cycle being the most profoundly perturbed pathway. Biochemical assays confirmed that apigenin markedly decreased the activities of four key TCA cycle enzymes: isocitrate dehydrogenase (ICDHc, 40.09% reduction), α-ketoglutarate dehydrogenase (α-KGDH, 39.26% reduction), succinate dehydrogenase (SDH, 97.66% reduction), and malate dehydrogenase (MDH, 85.86% reduction). Molecular docking further supported the potential interaction between apigenin and these TCA cycle-related enzymes. Collectively, our findings suggest that apigenin inhibits C. sakazakii growth in association with the inhibition of key TCA cycle enzymes, which may contribute to the disruption of central carbon metabolism and ATP biosynthesis, ultimately leading to bacterial metabolic dysfunction and growth inhibition.