ε-Polylysine Inhibits Shewanella putrefaciens with Membrane Disruption and Cell Damage

epsilon -Polylysine (epsilon -PL) was studied for the growth inhibition of Shewanella putrefaciens (S. putrefaciens). The minimal inhibitory concentration (MIC) of epsilon -PL against S. putrefaciens was measured by the broth dilution method, while the membrane permeability and metabolism of S. putrefaciens were assessed after epsilon -PL treatment. Additionally, growth curves, the content of alkaline phosphatase (AKP), the electrical conductivity (EC), the UV absorbance and scanning electron microscope (SEM) data were used to study cellular morphology. The impact of epsilon -PL on cell metabolism was also investigated by different methods, such as enzyme activity (peroxidase [POD], catalase [CAT], succinodehydrogenase [SDH] and malic dehydrogenase [MDH]) and cell metabolic activity. The results showed that the MIC of epsilon -PL against S. putrefaciens was 1.0 mg/mL. When S. putrefaciens was treated with epsilon -PL, the growth of the bacteria was inhibited and the AKP content, electrical conductivity and UV absorbance were increased, which demonstrated that epsilon -PL could damage the cell structure. The enzyme activities of POD, CAT, SDH, and MDH in the bacterial solution with epsilon -PL were decreased compared to those in the ordinary bacterial solution. As the concentration of epsilon -PL was increased, the enzyme activity decreased further. The respiratory activity of S. putrefaciens was also inhibited by epsilon -PL. The results suggest that epsilon -PL acts on the cell membrane of S. putrefaciens, thereby increasing membrane permeability and inhibiting enzyme activity in relation to respiratory metabolism and cell metabolism. This leads to inhibition of cell growth, and eventually cell death.