Abstract: Cross streak, radial streak, agar diffusion and co-culture methods were used to assess the antimicrobial activity of various probiotics and their metabolites against four representative foodborne pathogenic bacteria. The probiotic strains with great antibacterial activity against both Gram-positive pathogens (Listeria monocytogenes and Staphylococcus aureus) and Gram-negative pathogens (Escherichia coli and Salmonella typhimurium) were screened out. They were incorporated into polymeric materials (hydroxypropyl cellulose, glycerol and konjac flour) to develop bacteriostatic films, and the probiotic viability and the antimicrobial effects of films were measured. The consistent results obtained from cross streak and radial streak tests showed that Lactobacillus and Enterococcus especially Lactobacillus paracasei CICC 20241 exhibited high antibacterial activity against four target pathogens; the agar diffusion test showed that the lactic acid bacteria culture (LC), cell-free supernatant (CFS), and bacterial cells (BC) of L. paracasei CICC 20241 all had great antibacterial effect, and the co-culture test showed that L. paracasei CICC 20241 exhibited higher growth activity and antagonistic activity when inoculated earlier than the pathogens. In addition, the bacteriostatic film prepared in this experiment was a good carrier for L. paracasei CICC 20241, which was suitable for the survival of the Lactobacillus strain and exhibited continuous antibacterial activity against the target pathogens. The Lactobacillus film may have a great application potential for the development of packaging materials for fresh foods.

Key words: probiotics, antimicrobial activity, pathogens, bioactive composite film