Listeria monocytogenes (L. monocytogenes) is one of gram-positive foodborne pathogens with a very high fatality rate. Unlike most foodborne pathogens, L. monocytogenes is capable of growing at low temperatures, such as in refrigerated foods. Thus, various physical and chemical prevention methods are used in the manufacturing, processing and distribution of food. However, there are limitations to the methods such as possible changes to the food quality and the consumer awareness of synthetic preservatives. Thus, the aim of this study was to evaluate the anti-listeria activity of lactic acid bacteria (LAB) isolated from kimchi and characterize the bacteriocin produced by Lactococcus lactis which is one of isolated strains from kimchi. The analysis on the anti-listeria activity of a total of 36 species (Lactobacillus, Weissella, Lactobacillus, and Lactococcus) isolated from kimchi by the agar overlay method revealed that L. lactis NJ 1-10 and NJ 1-16 had the highest anti-listeria activity. For quantitatively analysis on the anti-listeria activity, NJ 1-10 and NJ 1-16 were co-cultured with L. monocytogenes in Brain Heat Infusion (BHI) broth, respectively. As a result, L. monocytogenes was reduced by 3.0 log CFU/mL in 20 h, lowering the number of bacteria to below the detection limit. Both LAB strains showed anti-listeria activity against 24 serotypes of L. monocytogenes, although the sizes of clear zone was slightly different. No clear zone was observed when the supernatants of both LAB cultures were treated with proteinase- K, indicating that their anti-listerial activities might be due to the production of bacteriocins. Heat stability of the partially purified bacteriocins of NJ 1-10 and NJ 1-16 was relatively stable at 60oC and 80oC. Yet, their anti-listeria activities were completely lost by 60 min of treatment at 100oC and 15 min of treatment at 121oC. The analysis on the pH stability showed that their anti-listeria activities were the most stable at pH 4.01, and decreased with the increasing pH value, yet, was not completely lost. Partially purified bacteriocins showed relatively stable anti-listeria activities in acetone, ethanol, and methanol, but their activities were reduced after chloroform treatment, yet was not completely lost. Conclusively, this study revealed that the bacteriocins produced by NJ 1-10 and NJ 1-16 effectively reduced L. monocytogenes, and that they were relatively stable against heat, pH, and organic solvents, therefore implying their potential as a natural antibacterial substance for controlling L. monocytogenes in food.

Lacticin NK34 is a small nisin-like bacteriocin present in the supernatants of an isolate of Lactococcus lactis from jeotgal, a salted and fermented Korean food made with seafood such as shrimp, oysters, and fish. Recently, we demonstrated that a partially purified NK34 is highly effective against various Staphylococcus species in a murine infection model. In this study, the two major bacterial pathogens associated with bovine mastitis, Streptococcus aureus and S. agalactiae, were evaluated for their susceptibility to NK34 in vitro using a standard teat-dip assay as well as in vivo using mastitic cows infected with one of these pathogenic strains. The experimental analyses showed a significant decrease (up to 98 times) in the bacterial numbers between the NK34-treated and -untreated teats. Moreover, a dramatic reduction in somatic cell counts was observed at 3 days post-treatment with 10 ml of NK34 administered directly into the mastitic cows. Neither S. aureus nor S. agalactiae were recovered. Taken together, these results imply that lacticin NK34 is an alternative antimicrobial substitute for the treatment of bovine mastitis, caused especially by either S. aureus or S. agalactiae.

Lactococcus lactis subsp. lactis ATCC l1454의 유산균 배양액을 3.96 log units, 4.10 log units 및 4.23log units의 농도로 처리한 돼지고기 등심은 4℃ 저장 9일 동안 호기성 부패세균의 증식억제와 저장 안정성 증진 가능성을 나타내었다. 유산균 배양액 처리구는 4℃ 저장 3일 동안 대조구 보다 유의적으로 낮은 pH 가를 나타내었다 유산균 배양액으로 처리한 돼지고기 등심의 외관과 냄새에 대한 관능평가 결과는 4℃ 저장 9일 동안 신선한 대조구와 유사하거나 보다 낮게 좋은 것으로 등급되었다.

돼지고기 등심의 표면에 Lcatococcus lactis subsp lactis ATCC l1454 유산균 배양액 3.96 log units의 처리구는 4℃ 저장 1일 이후 대조구의 TBA가와 유의적 차이가 없었다 (P>0.05). 유산균 배양액 3.96 log units 처리구의 Hunter color L^*과 b^*가는 저장 동안 대조구와 유의적 차이가 없었다. 그러나 유산균 배양액 4.10과 4.23 log units 처리구의 Hunter a^*가는 4℃ 저장 1일과 6일 이후 대조구와 유의적 차이 (P<0.05)를 나타내었다. 유산균 배 양액 4.10과 4.23 log units 처리구의 육즙유출율은 4℃ 저장 4일 이후부터 처리구와 대조구 사이에 유의적 차이를 나타내었다.

This study sought to confirm the inhibitory ability of Clostridioides difficile KCTC 5009 strain using the bacteriocin-producing Lactococcus lactis CJNU 3001 strain. For this purpose, bacterial culture and partially purified bacteriocin verified the antibacterial activity against C. difficile strain. As a result, both samples showed strong antibacterial activity against the target strain. Co-culture tests were performed to more closely analyze the competition between the two strains. As a result, a similar inhibitory effect was confirmed in RCM broth and CMM (colon model medium) broth. In particular, inhibition of C. difficile KCTC 5009 strain was not observed until the exponential phase of the growth of L. lactis CJNU 3001 strain, because bacteriocins were produced during that period. It was inferred that it actively suppressed the growth of the target strain after that. Therefore, as it was proven that the bacteriocin-producing L. lactis CJNU 3001 strain can effectively control C. difficile strain in co-cultures, it was judged that it could be an alternative for CDI (Clostridioides difficile infection) treatment.