Short communication: Bacteriocin KC24 produced by Lactococcus lactis KC24 from kimchi and its antilisterial effect in UHT milk.

The severity of Listeria monocytogenes infections emphasizes the need for prevention or elimination of the pathogen from dairy products. Lactococcus lactis KC24, isolated from kimchi, exhibited an antimicrobial effect against food pathogens, including L. monocytogenes ATCC 15313. Lactococcus lactis KC24 was cultured in a 5-L jar fermenter at 35°C, and bacteriocin activity was maximal at 4 h of incubation and persisted for 20 h. Bacteriocin KC24 was inactivated by protease XIV, indicating that it has a proteinaceous nature. Bacteriocin activity was maintained at pH 3.0 to 9.0 and at temperatures of 50 to 121°C. The mode of inhibition against L. monocytogenes ATCC 15313 was shown to involve a bactericidal effect by treatment with 100 and 200 arbitrary units (AU)/mL of bacteriocin KC24. To test the activity of bacteriocin KC24 in a food product, bacteriocin KC24 and nisin (100 and 200 AU/mL) with 4 log cfu/mL of a mixed culture of L. monocytogenes (ATCC 15313, ScottA, H7962, and H7762) were applied to UHT milk. Compared with the control, treatment with bacteriocin KC24 completely inhibited the growth of L. monocytogenes and resulted in no detectable L. monocytogenes after 14 d at 4°C, whereas nisin moderately inhibited L. monocytogenes, resulting in a final concentration after 14 d at 4°C higher than the initial inoculum. Bacteriocin KC24 may prove useful in improving the safety of dairy products.