Lactobacillus casei LDJ is an excellent strain that can inhibit the growth of Proteusbacillus vulgaris.To investigate the antibacterial effect of the cell-free supernatant of Lactobacillus casei LDJ,the antibacterial ability of cell-free supernatant with different fermentation time on Proteusbacillus vulgaris was tested by the Oxford cup method.When the fermentation time was 0-4 h,the cell-free supernatant had no antibacterial ability.The antibacterial ability increased gradually after fermentation of 8 h and tended to be stable when fermentation time was 24-48 h.Specifically,when the fermentation time was 36 h,the diameter of the antibacterial zone was the largest(20.48 mm).The research on physicochemical properties of the antibacterial substances in the cell-free supernatant of Lactobacillus casei LDJ shows that the antibacterial substance has various inhibitory effects on Escherichia coli,Staphylococcus aureus,and Listeria monocytogenes.The cell-free supernatant still has good antibacterial activity after treatment at 40-100℃for 30 min.The antibacterial substance has a good antibacterial effect in the range of pH value 3-6 but shows no antibacterial effect under neutral and alkaline conditions.Different enzyme treatments have different effects on the antibacterial effect of cell-free supernatant.Therefore,it is speculated that the effective antibacterial components of Lactobacillus casei LDJ may be peptides and organic acids.
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