• Microbiology and Biotechnology Letters
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• v.19 no.6
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• pp.619-623
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• 1991

To investigate nisin production and resistance of Lactococcus lactis ssp. tactis ML (L. lactis $ML_8$, effects of medium, pH of culture broth, and cell growth on the nisin activity, and effect of nisin with or without $Ca^[2+}$ ion on the growth of L. lactzs were analyzed. In the bio-assay of nisin by the agar diffusion method, inhibition-zone diameter of Micrococcus Javus was propotional to the logarithm of nisin concentration ranged 0.5~20 unitlml (12.5~500 ng/mf). Nisin activity of the pasteurized culture filtrates of L. lactis MLs was high at pH 2!3 but was inactivated completely at pH over 6.0. Nisin production of the L. lactis $ML_8$ cultured on LTB broth increased at late logarithmic phase and reached 10.5 unitlml after 16 hr. The cell growth of L. lactis LM 0230, a plasmid free and nisin sensitive strain, was inhibited on agar medium containing 7 unitlrnl of nisin, while L. lactis $ML_8$ showed high survival ability at 20 unitld of nisin. When 40 mM $Ca^[2+}$ ion was added to Elliker broth with 8 unitlml of nisin, the growth pattern of L. lactis $ML_8$ was similiar to that on control medium which did not contain nisin and $Ca^[2+}$ ion, and this suggested that $Ca^[2+}$ increased the nisin resistance of the L. lactis.

• Microbiology and Biotechnology Letters
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• v.40 no.4
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• pp.310-318
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• 2012

We conducted a screening and checked the cultivation methods of lactic acid bacteria, which have anti-atopic dermatitis functions, by determining the lactic acid bacteria's immune enhancement by FACS, and antimicrobial activity against Staphylococcus aureus. The increase of Tcell CD4+/CD25+/foxp3+ was bigger in Lactobacillus plantarum than Lactococcus lactis subsp. lactis (Lc. lactis) and the antimicrobacterial activity against S. aureus was the opposite. The antimicrobial activity of Lb. plantarum culture with medium containing Lc. lactis culture broth was not enhanced, but the antimicrobial activity of Lc. lactis cultured in a medium containing Lb. plantarum culture broth was enhanced. As the optimal method caltivation of Lc. lactis in a medium containing 10% of heat-killed Lb. plantarum culture broth was chosen. By this method, the antibacterial activity of the pure Lc. lactis culture increased sharply at the end of the log phase, while a restraint effect on the growth of S. aureus increased 1.29 times.

• Journal of Microbiology and Biotechnology
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• v.3 no.4
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• pp.217-223
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• 1993

To investigate the nature and location of the nisin-resistance determinant of Lactococcus lactis subsp. lactis 7962 (L. lactis 7962), a total plasmid DNA prepared from L. lactis 7962, a nisin producer, was used to transform L. lactis subsp. lactis LM0230, a plasmid-free and nisin-sensitive strain, by protoplast mediated transformation procedures. All of the nisin-resistant transformants acquired the ability to utilize sucrose at the same time, confirming the close linkage between these two determinants in L. lactis 7962. The plasmid DNA profiles of a few selected nisin-resistant transformants were examined by agarose gel electrophoresis. No common plasmid was found among the transformants and some small plasmids previously not present in L. lactis 7962 were detected. These transformants were named as L. lactis KL1, KL2, KL3, KL4, or KL5, respectively based on their plasmid profiles. Growth curves of all transformants were similar to that of L. lactis LM0230, but different from that of L. lactis 7962. L. lactis KL5 showed the highest level of resistance to nisin, growing up to 1, 200 IU nisin/ml after 40 hr incubation. Some nisin-sensitive derivatives of KL1 or KL2 were obtained by plasmid curing experiments. The plasmid DNA profiles of the nisin-sensitive KL1 derivatives were apparently the same as that of the KL1. All of the nisin-sensitive KL2 derivatives were plasmid-free, but a nisin-resistant strain with no apparent plasmid was also obtained. These results indicate that the nisin-resistance of the $Nis^r$ transformants is presumably mediated by the chromosomally located gene(s) rather than plasmid-encoded gene(s).

• Journal of Microbiology and Biotechnology
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• v.26 no.11
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• pp.1829-1835
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• 2016

Dental caries is caused by cariogenic biofilm, an oral biofilm including Streptococcus mutans. Recently, the prevention of dental caries using various probiotics has been attempted. Lactococcus lactis HY 449 is a probiotic bacterium. The aim of this study was to investigate the effect of L. lactis HY 449 on cariogenic biofilm and to analyze its inhibitory mechanisms. Cariogenic biofilm was formed in the presence or absence of L. lactis HY 449 and L. lactis ATCC 19435, and analyzed with a confocal laser microscope. The formation of cariogenic biofilm was reduced in cultures spiked with both L. lactis strains, and L. lactis HY 449 exhibited more inhibitory effects than L. lactis ATCC 19435. In order to analyze and to compare the inhibitory mechanisms, the antibacterial activity of the spent culture medium from both L. lactis strains against S. mutans was investigated, and the expression of glucosyltransferases (gtfs) of S. mutans was then analyzed by real-time RT-PCR. In addition, the sucrose fermentation ability of both L. lactis strains was examined. Both L. lactis strains showed antibacterial activity and inhibited the expression of gtfs, a nd t he d ifference b etween both strains did not show. In the case of sucrose-fermenting ability, L. lactis HY 449 fermented sucrose but L. lactis ATCC 19435 did not. L. lactis HY 449 inhibited the uptake of sucrose and the gtfs expression of S. mutans, whereby the development of cariogenic biofilm may be inhibited. In conclusion, L. lactis HY 449 may be a useful probiotic for the prevention of dental caries.

• Microbiology and Biotechnology Letters
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• v.26 no.6
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• pp.562-565
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• 1998

Nisin-producing and nisin resistant L. lactis subsp. lactis ATCC7962 harbored six plasmids. To find a plasmid containing a nisin resistant gene, these plasmids were transformed into L lactis LM0230 of plasmid-free and nisin sensitive strain. After screening on nisin selection media containing nisin (150 $\mu\textrm{g}$/$m\ell$), several nisin resistant transformants were obtained and the level of nisin resistance was very similar to that of wild type L lactis subsp. lactis ATCC7962. A 26.5 kb plasmid, named as pCS100, which confers resistance to nisin, was identified in transformants. The pCS100 was digested with EcoRI and Southern blot hybridization was done with nisI probe to localize the nisin resistant gene. A 4 kb EcoRI fragment showed a strong positive signal, and it was cloned into pBluescript for the potential selection marker.

• Journal of Pharmaceutical Investigation
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• v.35 no.2
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• pp.75-80
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• 2005

A promising application of Lactococcus lactis is its use as live vehicles for production and delivery of heterologous proteins of vaccines and therapeutic substances. Because L. lactis has GRAS ('generally regarded as safe') status, we tested whether L. lactis could function as the carrier of the Ll protein of human papillomavirus (HPV) type 16. The RNA level expression of Ll gene was detected in L. Lactis. The Ll protein was expressed in L. lactis with Ll gene. The growth of strains L. lactis with an empty plasmid (pAMJ328) and L. lactis with Ll-encoding plasmid (pAMJ328-Ll) was slightly decreased in comparison with the growth of strains L. lactis (wild type). However, all the three strains of L. lactis maintained the ability to ferment sugars primarily into lactic acid, indicating that Ll protein did not affect the biochemical property of L. lactis. These results suggest that L. lactis, capable of carrying Ll protein, might be further developed as a biocompatible oral protein delivery system.

• Preventive Nutrition and Food Science
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• v.5 no.3
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• pp.153-159
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• 2000

A 4.4 kb DNA fragment encompassing lacA (galactoside acetyltransferase) and lacZ($\beta$-galactosidase) genes from Lactococus lactis ssp. lactis ATCC 7962 (L. lactis 7962) was introduced ito a Lac strain, Lactococcus lactis ssp. lactis MG1363 (L. lactis MG1363) by using a lactococcal expression vector, pMG36e and expression level of lacZ was examined. Growth rates and $\beta$-galactosidase ($\beta$-gal) activities of MG1363 cells carrying recombinant plasmid, pMLZ3, on M17 broth containing different carbon sources (1%, w/v) were examined. Contrary to the expectations, MG1363 [pMLZ3] grown on lactose showed the lowest enzyme activity (17 units) and cells grown on galactose had the highest $\beta$-gal activity (41 units). Cells grown on glucose had intermediate activity (33 units). These activities are about one tenth of the values observed in L. lactis 7962 where lacZ is present as a single-copy gene in the chromosome. When the cellular concentrations of lacZ transcript were examined using slot blot hybridization, it was found that MG1363[pMLZ3] produced sufficient amounts of transcript. These results indicate that either proteolytic degradation of $\beta$-gal or other regulatory mechanism prevent the translation or accumulation of $\beta$-gal in L. lactis MG1363 cells. In regard to regulation, the presence of the ccpA gene in L. lactis MG1363 was confirmed by Southern blot.

• Microbiology and Biotechnology Letters
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• v.33 no.4
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• pp.241-247
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• 2005

A new lactococcal shuttle/expression vector for lactococci, pWgal13T, was constructed using a $\beta$-galactosi-dase gene (lacZ) from Lacfococcus lactis ssp. lactis ATCC 7962 as a screening marker. The pWgal 13T was introduced into Escherichia coli DH5a and L. lactis MG1363, and was easily detected by the formation of blue colonies on a medium containing X-gal without any false transformants. Also, the quantitatively lacZ activity of pWgal13T was measured in L. lactis ssp. cremoris MG1363, and was found to be four times higher than that of L. lactis ssp. lactis ATCC7962 grown on a medium containing glucose, which shows that the lacZ gene of pWgal13T can be used for the efficient screening of L. lactis on general media. The pWgal13T was equipped with a lactococcal replicon of pWV01 from L. lactis Wg2, the new promoter P13C from L. lactis ssp. cremoris LM0230, multiple cloning sites, and a terminator for the expression of a relevant gene. The vee-tor pWgal13T was used for the expression of the EGFP gene in E. coli and L. lactis. These results show that the lactococcal expression/shuttle vector constructed in the present study can be used for the production of foreign proteins in E. coli and L. lactis.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.4
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• pp.549-557
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• 2000

Dental caries is a bacterial disease of the dental hard tisssus, characterized by a localized, progressive, molecular disintegration of tooth structure. The action of Leuconostoc lactis 51 about plaque formation and replication by Streptococcus mutans was studied as follows. 1. Lower amount of plaque was produced at the mixed culture of S. mutans and L. lactis 51 than S. mutans alone on the wires in the beaker. 2. Fewer cells of S. mutans were replicated at the mixed culture of S. mutans and L. lactis 51 than S. mutans alone. 3. In M17Y broth, viable cells of S. mutans and L. lactis 51 increased for 12 hours, and decreased for 24 hours. In M17YS broth, viable cells of S. mutans showed time-dependent decrease at mixed culture of S. mutans and L. lactis 51. 4. The culture supernatant of L. lactis 51 didn't inhibit the replication of S. mutans and the formation of artificial plaque. 5. Sucrose and frutose were extracted from the culture supernatant of L. lactis 51 in M17YS broth. These results suggest that L. lactis 51 isolated from the oral cavity inhibits the replication of S. mutans and the formation of artificial plaque.

• The Journal of the Korean Society for Microbiology
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• v.35 no.1
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• pp.77-85
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• 2000

Streptococcus mutans is the most important causative bacteria of dental caries among the oral bacteria. Lactococcus lactis 1370 was isolated from the oral cavity of child. The effect of Lactococcus lactis 1370 on the formation of artificial plaque by Streptococcus mutans was studied. 1. The insoluble substances and bacteria were much more attached on the wall of disposable cuvette in the culture of Streptococcus mutans than in the combined culture of Streptococcus mutans and Lactococcus lactis 1370. 2. The mean weight of produced artificial plaque on the wires in the beaker was 131.7 mg in the culture of Streptococcus mutans only, whereas being reduced to 6.4 mg in the combined culture of Streptococcus mutans and Lactococcus lactis 1370 (p<0.05). The viable cell didn't show the significant difference between them after culturing. 3. When Streptococcus mutans was cultured in the media containing culture supernatant of Lactococcus lactis 1370 cultured in M17 broth containing 0.5% yeast extract and 5% sucrose, the mean weight of produced artificial plaque was 8.0 mg on the wires, whereas being 125.4 mg in the media without culture supernatant of Lactococcus lactis 1370 (p<0.05). The viable cell didn't show the significant difference between them after culturing. 4. When Streptococcus mutans was cultured in the media containing soluble polymer produced by Lactococcus lactis 1370, the mean weight of produced artificial plaque was significantly reduced compared with being cultured in the media without soluble polymer (p<0.05). The viable cell didn't show the significant difference between them after culturing. 5. The soluble polymer produced by Lactococcus lactis 1370 was glucan. 6. The glucan produced by Lactococcus lactis 1370 was water-soluble glucan containing ${\alpha}$-1,6-glucose linkage as the main linkage. These results suggest that the artificial plaque formed by Streptococcus mutans is inhibited by water-soluble glucan produced by Lactococcus lactis 1370.