Lactic acid bacteria (LAB) can improve host health and has strong potential for use as a health functional food. Specific strains of LAB have been reported to exert immunostimulatory effects. The primary goal of this study was to evaluate the immunostimulatory activities of novel LAB strains isolated from humans and foods and to investigate the probiotic properties of these strains. Cell-free supernatants (CFS) obtained from selected LAB strains significantly increased phagocytosis and level of nitric oxide (NO) and pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 in RAW264.7 macrophage cells. The protein expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2, which are immunomodulators, was also upregulated by CFS treatment. CFS markedly induced the phosphorylation of nuclear factor-κB (NF-κB) and MAPKs (ERK, JNK, and p38). In addition, the safety of the LAB strains used in this study was demonstrated by hemolysis and antibiotic resistance tests. Their stability was confirmed under simulated gastrointestinal conditions. Taken together, these results indicate that the LAB strains selected in this study could be useful as probiotic candidates with immune-stimulating activity.

Probiotics restore gut microbial balance, thereby providing health-promoting effects to the host. They have long been suggested for managing intestinal disorders caused by pathogens and for improving gut health. This study evaluated the probiotic properties and anti-pathogenic effects of specific probiotic strains against the intestinal pathogens Staphylococcus aureus and Escherichia coli. The tested strains—Lactiplantibacillus plantarum LC27, Limosilactobacillus reuteri NK33, Lacticaseibacillus rhamnosus NK210, Bifidobacterium longum NK46, and Bifidobacterium bifidum NK175—were able to survive harsh conditions simulating gastric and intestinal fluids. These strains exhibited good auto-aggregation abilities (41.8–92.3%) and ideal hydrophobicity (30.9–85.6% and 38.3–96.1% for xylene and chloroform, respectively), along with the ability to co-aggregate with S. aureus (40.6–68.2%) and E. coli (38.6–75.2%), indicating significant adhesion levels to Caco-2 cells. Furthermore, these strains’ cell-free supernatants (CFSs) demonstrated antimicrobial and antibiofilm activity against S. aureus and E. coli. Additionally, these strains inhibited gas production by E. coli through fermentative activity. These findings suggest that the strains tested in this study have potential as novel probiotics to enhance gut health.

The modulation of the immune system is a major mechanism through which probiotics exert beneficial effects on health. Probiotics, including lactic acid bacteria (LAB), have been reported to enhance innate immunity. The purpose of this study was to screen for LAB strains with excellent immunostimulatory activity isolated from kimchi. We selected five promising strains (Limosilactobacillus fermentum MG5489, Lactococcus lactis MG5542, Lacticaseibacillus paracasei MG5559, Latilactobacillus sakei MG5468, and Latilactobacillus curvatus MG5609) that exhibited immune-stimulating effects by inducing the production of nitric oxide (NO) and pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β in RAW264.7 cells. The selected strains significantly increased phagocytic activity of RAW264.7 cells and nuclear factor-κB (NF-κB) activation. Furthermore, the safety of the selected strains was determined using hemolysis and antibiotic susceptibility tests. The stabilities and adhesion abilities of these strains in the gastrointestinal tract (GIT) were also determined. Taken together, these findings suggest that the strains selected in this study have the potential to be novel probiotics to enhance immunity.

Probiotics should possess specific properties to exert beneficial effects, and their safety must be ensured for human consumption. The purpose of this study was to evaluate the probiotic properties and safety of Limosilactobacillus mucosae NK41 and Bifidobacterium longum NK46 isolated from human feces in vitro. Both strains exhibited high resistance to simulated gastrointestinal fluid. Furthermore, probiotic-related cell surface characteristics including auto-aggregation and cell surface hydrophobicity were assessed by measuring the absorbance at a wavelength of 600 nm, which demonstrated good auto-aggregation ability and affinity for xylene, indicating their effective adhesion to Caco-2 cells. In addition, hemolytic, gelatinase, and β-glucuronidase activities were found to be negative in both strains. The susceptibility to nine commonly used antibiotics was assessed using the broth macrodilution method, which demonstrated that both strains were susceptible to all tested antibiotics. Furthermore, L. mucosae NK41 and B. longum NK46 produced significantly higher levels of L-lactate (71.8 ± 0.7% and 97.8 ± 0.4%) than D-lactate (28.2 ± 0.7% and 2.2 ± 0.4%, respectively). Using PCR amplification to investigate genes associated with virulence factors, we found that neither strain harbored any virulence genes. These findings suggest that L. mucosae NK41 and B. longum NK46 have the potential to be used as probiotics and are considered safe for human consumption.