Control of foodborne pathogens by bacteriocin-like substances from Lactobacillus spp. in combination with high pressure processing

Lactic acid bacteria (LAB) and their bacteriocins have been used as natural food preservatives but only few reports are available concerning inactivation of gram negative bacteria by LAB bacteriocins. The objectives of this study were (1) to screen food for bacteria with activity against gram-negative pathogens, (2) to measure the sensitivity of selected foodborne pathogenic targets to the new antimicrobial agents, (3) to evaluate a synergy between the antimicrobial agent and high pressure processing (HPP) against the targeted pathogens, and (4) to study the combined effect of antimicrobial agent and HPP on components of bacterial cell.; Lactobacillus curvatus OSY-HJC6 and L. casei OSY-LB6A were isolated from fermented foods and identified. The cell-free extracts (CFE) of these isolates showed inhibition against Escherichia coli p220, E. coli O157, Salmonella enerica serovar Enteritidis, Salmonella Typhimurium, and Listeria monocytogenes. The activity of the CFE from Lb. curvatus and Lb. casei was sensitive to pronase. The antimicrobial nature of CFE from both isolates was confirmed by eliminating the inhibitory effect of acid, hydrogen peroxide, and lytic bacteriophages.; Lactobacillus curvatus showed antimicrobial activity extracellularly and intracellulary. Lactobacillus casei produces broad-spectrum complex bacteriocin-like substances. The combination treatment of CFE (32 CEAU/ml) and HPP (350 MPa for 1--20 min) synergistically inactivated E. coli O157 strains including O157:H7 and L. monocytogenes in cell suspension. The CFE (100 CEAU/g) and HPP (500 MPa and 400 MPa, 1 min) showed synergistic effect against E. coli O157 strains and L. monocytogenes in meat product. The effectiveness of CFE in combination with high pressure processing was more pronounced against L. monocytogenes. Differential scanning calorimetry thermogram suggested that ribosome and DNA in Listeria were damaged by the presence of CFE during HPP. The synergy between the CFE of Lb. casei and HPP suggests potential use of the combination treatment in food applications.