The antimicrobial effects and synergistic antibacterial mechanism of the combination of ε-Polylysine and nisin against Bacillus subtilis

•Combined treatment of ε-PL and nisin resulted in antimicrobial synergism.•Combined treatment significantly damaged the morphology of bacterial cells.•ε-PL and nisin synergistically enhanced the permeability of the cell membrane.•The fluorescence spectrum revealed an interaction between ε-PL and DNA.•Nisin promoted the cellular uptake of ε-PL, facilitating the ε-PL-DNA interaction.

The aim of the present study was to evaluate the combined effects of ε-Polylysine (ε-PL) and nisin and investigate the synergistic action of these compounds against Bacillus subtilis (B. subtilis).The combination of ε-PL and nisin showed synergistic anti-microbial activity against Escherichia coli (E. coli), B. subtilis and Staphylococcus aureus (S. aureus). SEM and TEM microscopy revealed that combined treatment with ε-PL and nisin synergistically damaged the morphology of tested bacterial cells. Propidium iodide (PI) infiltration experiments indicated that combined treatment with ε-PL and nisin synergistically enhanced the permeability of the bacterial cell membrane, likely reflecting the inhibition of both Na+K+- and Ca++ Mg++-ATPase activities through these compounds. The fluorescence spectrum showed an interaction between ε-PL and DNA, but not between nisin and DNA. The mode of ε-PL in binding with DNA was similar to that of ethidium bromide (EB). These results indicated that the uptake of ε-PL into cells was promoted through nisin, and subsequently, ε-PL interacted with the intracellular DNA achieving a synergistic effect.