Abstract: In order to enhance the antibacterial activity of hen egg white lysozyme against gram-negative bacteria such as Escherichia coli ATCC25922 and DH5α, the antibacterial effect of lysozyme combined with each or both of the permeabilizers glycine and ethylenediaminetetraacetate (EDTA-Na2) was analyzed, and the outer membrane permeability and cell surface morphology of E. coli were also examined. The results showed that ATCC25922 was more sensitive to lysozyme than DH5α and its outer membrane permeability was higher than that of DH5α. Due to the combinatorial application with glycine or EDTA-Na2, the antimicrobial activity of lysoyme against both E. coli strains was obviously improved, which indicated the synergistic antibacterial effect of lysoyme and each of the permeabilizers. 1-N-phenylnaphthylamine (NPN) uptake assay showed that the outer membrane permeability of E. coli strains was increased when the cells were treated with lysozyme supplemented with cell permeabilizers. TEM image of ATCC 25922 cells also revealed the synergistic effect of lysozyme supplemented with cell permeabilizers on damaging cell surface structure. Therefore, improving the outer membrane permeability of E. coli is helpful for enhancing the antibacterial effect of lysozyme on the bacterium.

Key words: hen egg white lysozyme, glycine, EDTA-Na2, Escherichia coli, outer membrane permeability