DETECTION AND CHARACTERIZATION OF A BACTERIOCIN PRODUCED BY LACTOCOCCUS-LACTIS SUBSP CREMORIS-R ISOLATED FROM RADISH

Bacteria isolated from radish were identified as Lactococcus lactis su bsp. cremoris R and their bacteriocin was designated lactococcin R. La ctococcin R was sensitive to some proteolytic enzymes (proteinase-K, p ronase-E, proteases, pepsin, alpha-chymotrypsin) but was resistant to trypsin, papain, catalase, lysozyme and lipase, organic solvents, or h eating at 90 degrees C for 15, 30 and 60 min, or 121 degrees C for 15 min. Lactococcin R remained active after storage at -20 and -70 degree s C for 3 months and after exposure to a pH of 2-9. The molecular weig ht of lactococcin R was about 2.5 kDa. Lactococcin R was active agains t many food-borne pathogenic and food spoilage bacteria such as Clostr idium, Staphylococcus, Lister ln, Bacillus, Micrococcus Enterococcus, Lactobacillus, Leuconostoc, Streptococcus and Pediococcus spp., but wa s not active against any Gram-negative bacteria. Lactococcin R was pro duced during log phase and reached a maximum activity (1600 AU ml(-1)) at early stationary phase. The highest lactococcin R production was o btained in MRS broth with 0.5% glucose, at 6.5-7.0 initial pH values, 30 degrees C temperature and 18-24-h incubation times. Lactococcin R a dsorbed maximally to its heat-killed producing cells at pH 6-7 (95%). Crude lactococcin R at 1280 AU ml(-1) was bactericidal, reducing colon y counts of Listeria monocytogenes by 99.98% in 3 h. Lactococcin R sho uld be useful as a biopreservative to prevent growth of food-borne pat hogenic and food spoilage bacteria in ready-to-eat, dairy, meat, poult ry and other food products. Lactococcin R differs from nisin in having a lower molecular weight, 2.5 kDa vs 3.4 kDa, and in being sensitive to pepsin and a-chymotrypsin to which nisin is resistant.