Detection and characterization of a bacteriocin produced by Lactococcus lactis subsp. cremoris R isolated from radish.

ABSTRACT

Bacteria isolated from radish were identified as Lactococcus lactis subsp. cremoris R and their bacteriocin was designated lactococcin R. Lactococcin R was sensitive to some proteolytic enzymes (proteinase-K, pronase-E, proteases, pepsin, alpha-chymotrypsin) but was resistant to trypsin, papain, catalase, lysozyme and lipase, organic solvents, or heating 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 degrees C for 3 months and after exposure to a pH of 2-9. The molecular weight of lactococcin R was about 2.5 kDa. Lactococcin R was active against many food-borne pathogenic and food spoilage bacteria such as Clostridium, Staphylococcus, Listeria, Bacillus, Micrococcus, Enterococcus, Lactobacillus, Leuconostoc, Streptococcus and Pediococcus spp., but was not active against any Gram-negative bacteria. Lactococcin R was produced during log phase and reached a maximum activity (1600 AU ml-1) at early stationary phase. The highest lactococcin R production was obtained 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 adsorbed maximally to its heat-killed producing cells at pH 6-7 (95%). Crude lactococcin R at 1280 AU ml-1 was bactericidal, reducing colony counts of Listeria monocytogenes by 99.98% in 3 h. Lactococcin R should be useful as a biopreservative to prevent growth of food-borne pathogenic and food spoilage bacteria in ready-to-eat, dairy, meat, poultry 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 alpha-chymotrypsin to which nisin is resistant.