Application of bacteriocins produced by lactic acid bacteria in preserving dairy products and development of a selective medium for Leuconostoc isolation

creening lactic acid bacteria for bacteriocin production against Listeria monocytogenes was carried out with 324 strains isolated from different sources. Four of the five producer strains were identified as Lactococcus lactis subsp. lactis and the fifth was a Lactobacillus species. Antimicrobial substance produced by three of the Lc. lactis strains was nisin. The fourth (lactococcin LBIIA) was unique and differed from nisin by sensitivity to trypsin and ;Nisin was lethal to nine strains of three species of Listeria, including pathogenic L. monocytogenes. Effect of nisin on L. monocytogenes in cottage cheese and yogurt was investigated. Nisin inhibited this pathogen in both products. Fermentation of milk by Streptococcus thermophilus and Lactobacillus bulgaricus to produce yogurt was inhibited by nisin at concentrations higher than 50 IU/ml; less than 50 IU/ml could be used to inhibit growth of L. monocytogenes in yogurt and cottage cheese.;Use of nisin at 40 IU/ml to extend the shelf-life of Feta cheese manufactured with starter containing S. thermophilus and L. bulgaricus also was studied. In comparison to control cheese made without nisin, the nisin-containing cheese actually spoiled more rapidly, apparently by limiting the growth of L. bulgaricus and allowing contaminating Gram-negative psychrotrophs to grow with less competition.;Attempts to study bacteriocin production by dairy Leuconostoc (Leu) strains isolated from natural vegetation was hindered by the unavailability of a suitable selective isolation medium. Such an effective medium, was formulated containing 1% glucose, 1% bacto peptone, 0.5% yeast extract, 0.5% beef extract, 0.25% gelatin, 0.5% calcium lactate, 0.05% sorbic acid, 75...