Isolation and Antibacterial Properties of Lactic Acid Bacteria Exhibiting Antagonistic Effects against Food Spoilage Bacteria

The 124 strains of lactic acid bacteria in this study were screened for antibacterial activities against food spoilage bacteria. All lactic strains were fermented for 3-5 days in 10% reconstituted skim milk supplemented with 0.5% yeast extract and 0.5% glucose. Culture filtrates from skim milk media adjusted to pH 4.5, centrifuged at 15,000-rpm and filter-sterilized for antagonistic activities by paper disc assays, using Escherichia coli, Pseudomonas fragi, Staphylococcus aureus and Bacillus subtilis as test organisms. One out of 124 lactic strains showed greater inhibitory activities against the 4 test organisms. The strain from lnner Mongolian cheese, designated as IMC-1, belonged to the Lactobacillus acidophilus group and was selected for further studies. This strain showed considerable inhibitory effects against other lactic strains such as Lactobacillus helveticus and Streptococcus thermophilus under conditions that reduced the effects of organic acids. The antibacterial activities against Pseudomonas fragi IFO 3458 were lost at more than ph 5.2 and remaining inhibition rate after treatments at 121℃ for 20 min was approximately 63.5%. The antibacterial substance was extracted from skim milk culture filtrates with ethanol and was passed through Sephadex G-25 columns. It was presumed to be a bacteriocin-like substance with a moleculr weight of 1,000～3,500.