Antibacterial Effects and Mechanisms of Three Polyphenols against Shewanella putrefaciens

This study was performed to investigate the inhibitory mechanisms of 3 plant polyphenols, grape seed extract (GSE), lotus seed proanthocyanidins (LSPC) and lotus root polyphenol extract (LRPE), against Shewanella putrefaciens. Their antibacterial effects were determined in terms of minimum inhibitory concentration (MIC) and the growth curve of S. putrefaciens. By scanning electron microscopy (SEM), relative conductivity, propyridine iodide (PI) staining, alkaline phosphatase (AKP) activity, extracellular protein content, nucleic acid leakage, Na⁺ K⁺ -ATPase activity and membrane protein fluorescence analysis, the antibacterial mechanism was explored. The results showed that the MICs of GSE, LRPE and LSPC were 31.25, 62.25 and 125.00 μg/mL, respectively. After S. putrefaciens was treated with the polyphenols, the position of membrane proteins was changed, the fluorescence intensity was reduced, the morphology was altered, the surface became wrinkled and sunken, and the growth was significantly inhibited. In addition, the activity of extracellular AKP, the contents of nucleic acid and extracellular protein in the bacterial suspension, relative conductivity and PI intake were significantly increased, and Na⁺ K⁺-ATPase was inactivated to a certain extent, thereby leading to cell death.