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In this study, we investigated the antimicrobial effect of tea polyphenols (TP) against Serratia marcescens and examined the related mechanism. Morphology changes of S. marcescens were first observed by transmission electron microscopy after treatment with TP, which indicated that the primary inhibition action of TP was to damage the bacterial cell membranes. The permeability of the outer and inner membrane of S. marcescens dramatically increased after TP treatment, which caused severe disruption of cell membrane, followed by the release of small cellular molecules. Furthermore, a proteomics approach based on two-dimensional gel electrophoresis and MALDI-TOF/TOF MS analysis was used to study the difference of membrane protein expression in the control and TP treatment S. marcescens. The results showed that the expression of some metabolism enzymes and chaperones in TP-treated S. marcescens significantly increased compared to the untreated group, which might result in the metabolic disorder of this bacteria. Taken together, our results first demonstrated that TP had a significant growth inhibition effect on S. marcescens through cell membrane damage.

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To obtain the antibacterial agents with long-acting and slow-release properties, the microcapsules were prepared with tea polyphenols (TP), ϵ-poly-L-lysine hydrochloride (ϵ-PL) and TP/ϵ-PL as core materials. Meanwhile, the microcapsules were characterised, their release properties were measured, and their antimicrobial mechanisms against Shewanella putrefaciens were studied. At the initial release phase, TP and ϵ-PL are competitively released from the composite microcapsules. The release of TP and ϵ-PL is both fitted to the logistic model, indicating that the primary release mechanism is the disintegration and dissolution. The long-acting antibacterial properties of the microcapsules are better than those of the free antibacterial agent. The microcapsules can destroy the integrity of the cell membrane, and make the permeability improve. Also, the synthesis and expression of bacterial proteins are inhibited. Because of longterm antibacterial properties, the microcapsules have potential value for application in the preservation of food.