Organic acids are natural antimicrobial compounds commonly used in the food industry. In this study, acetic, lactic, butyric, citric, and malic acid at minimum inhibitory concentrations and their combinations at optimal inhibition concentrations were used to treat E. coli, and the effects on the cell barrier and biofilm of E. coli were evaluated. Acetic acid showed the highest membrane-damaging effect, while citric acid and malic acid could specifically damage the cell wall of E. coli, leading to alkaline phosphatase leakage. The RT-qPCR results showed that organic acids upregulated the membrane-protein-related genes of E. coli, and the combination of organic acids had a wider range of effects than single organic acid treatment. Moreover, organic acids inhibited the formation of E. coli biofilm and cellular activity within the biofilm. This study showed that the combination of organic acids plays a synergistic inhibitory role mainly through multiple destructive effects on the cell barrier and exhibited synergistic anti-biofilm effects. The three-three combination of acetic, lactic acid, and a third organic acid (butyric, citric, or malic) can play a better synergistic antibacterial effect than the two-pair combination of acetic and lactic acid. These findings have implications for the usage, development, and optimization of organic acid combinations.

中文翻译：

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不同有机酸及其组合对大肠杆菌细胞屏障和生物膜的影响。

有机酸是食品工业中常用的天然抗菌化合物。本研究采用最低抑制浓度的乙酸、乳酸、丁酸、柠檬酸、苹果酸及其最佳抑制浓度的组合来处理大肠杆菌，并评价其对大肠杆菌细胞屏障和生物膜的影响。乙酸对细胞膜的破坏作用最强，而柠檬酸和苹果酸则可以特异性破坏大肠杆菌的细胞壁，导致碱性磷酸酶渗漏。RT-qPCR结果表明，有机酸上调大肠杆菌膜蛋白相关基因，且有机酸组合比单一有机酸处理具有更广泛的作用。此外，有机酸抑制大肠杆菌生物膜的形成和生物膜内的细胞活性。本研究表明，有机酸组合主要通过对细胞屏障的多重破坏作用发挥协同抑制作用，表现出协同抗生物膜作用。醋酸、乳酸和第三种有机酸(丁酸、柠檬酸或苹果酸)的三三组合比醋酸和乳酸的两对组合能起到更好的协同抗菌效果。这些发现对有机酸组合的使用、开发和优化具有重要意义。