Antibacterial property of bacteriocin produced by Lactobacillus plantarum LD4 isolated from a fermented food

Bacteriocins are ribosomally synthesized antimicrobial peptides secreted by certain lactic acid bacteria, with potential application in food safety. Bacteriocin-producing Lactobacillus plantarum LD4 was identified using biochemical and molecular techniques including 16S rDNA amplification, followed by sequencing. Bacteriocin production started after 3 h, reaching a maximum during the early stationary phase. Bacteriocin present in cell-free supernatant showed stability in a pH range of 2.0 to 6.0, as well as at different temperatures (60-100 and 121 A degrees C for 15 min under 15 psi pressure). Antimicrobial activity was not affected by catalase, lipase or alpha-amylase, but was reduced in the presence of trypsin and protease, suggesting the proteinaceous nature of the compound. Activity remained stable after treatment with different organic solvents, surfactants, and detergents. The molecular weight of bacteriocin LD4 was found to be similar to 6 kDa using tricine SDS-PAGE. Antimicrobial activity was demonstrated against Gram-positive and Gram-negative bacteria including Micrococcus luteus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Vibrio sp., Enterobacter cloacae, Enterococcus faecium, and a few strains of lactic acid bacteria and haloarchaea. Bacteriocin LD4 caused K+ ion efflux in target cells, suggesting the pore-forming nature of the compound. Given the stability under various conditions and the broad antimicrobial spectrum against pathogens, the bacteriocin LD4 has the potential for application in food safety as well as therapeutics.