Heat-Killed Lactobacillus brevis Enhances Phagocytic Activity and Generates Immune-Stimulatory Effects through Activating the TAK1 Pathway.

There is an increasing interest in using inactivated probiotics to modulate the host immune system and protect against pathogens. As the immunomodulatory function of heat-killed Lactobacillus brevis KCTC 12777BP (LBB) and its mechanism is unclear, we investigated the effect of LBB on immune response based on the hypothesis that LBB might exert stimulatory effects on immunity. In the current study, we demonstrate that administration of LBB can exert immune-stimulatory effects and promote clearance of foreign matters through enhancing phagocytosis. Treatment with LBB induced the production of TNF-α, IL-6, and nitric oxide in macrophages. Importantly, LBB directly increased the phagocytic activity of macrophages against bacterial particles. LBB was able to promote the production of TNF-α in bone marrow-derived macrophages and splenocytes and also increase the proliferation rate of splenocytes, suggesting that the immune-stimulating activity of LBB can be observed in primary immune cells. Investigation into the molecular mechanism responsible revealed that LBB upregulates TAK1 activity and its downstream ERK, p38, and JNK signaling pathways. To further confirm the immunomodulatory capability of LBB in vivo, we orally administered LBB to mice and assessed the effect on primary splenocytes. Splenocytes isolated from LBB-treated mice exhibited higher TNF-α expression and proliferative capacity. These results show that heat-killed L. brevis, a wildly consumed probiotic, may provide protection against pathogens through enhancing host immunity.

Suitability of Lactobacillus plantarum SPC-SNU 72-2 as a Probiotic Starter for Sourdough Fermentation.

In sourdough fermentation, lactic acid bacteria perform important roles in the production of volatile and antimicrobial compounds, and exerting health-promoting effects. In this study, we report the probiotic properties and baking characteristics of Lactobacillus plantarum SPC-SNU 72-2 isolated from kimchi. This strain is safe to use in food fermentation as it does not carry genes for biogenic amine production (i.e., hdc, tdc, and ldc) and shows no ß-hemolytic activity against red blood cells. The strain is also stable under simulated human gastrointestinal conditions, showing tolerance to gastric acid and bile salt, and adheres well to colonic epithelial cells. Additionally, this strain prevents pathogen growth and activates mouse peritoneal macrophages by inducing cytokines such as tumor necrosis factor-α, interleukin (IL)-6, and IL-12. Furthermore, the strain possesses good baking properties, providing rich aroma during dough fermentation and contributing to the enhancement of bread texture. Taken together, L. plantarum SPC-SNU 72-2 has the properties of a good starter strain based on the observation that it improves bread flavor and texture while also providing probiotic effects comparable with commercial strains.

Development of species-specific PCR primers and polyphasic characterization of Lactobacillus sanfranciscensis isolated from Korean sourdough.

Lactobacillus sanfranciscensis is a bacterium used in sourdough that provides desirable properties such as better flavor and texture to the sourdough bread. Here, the intra-species diversity of L. sanfranciscensis strains isolated from Korean sourdough was studied using genotypic (multiplex-RAPD-PCR: multiplex-Randomly Amplified Polymorphic DNA-polymerase chain reaction) and phenotypic (VITEK2 Compact system) analyses. For this, a novel species-specific set of PCR primers was developed to identify L. sanfranciscensis using the recently published genome database. The primers were able to detect L. sanfranciscensis isolated from Korean sourdough with 100% accuracy. Genotyping and phenotyping analyses at the strain level demonstrated that Korean sourdough possesses various biotypes of L. sanfranciscensis strains. These strains were clustered into 5 subtypes (genotyping) or 7 subtypes (phenotyping). In summary, this strategy to construct novel primers reduced the chance of cross amplification and was able to identify the desired strain. The various strains isolated in this study can be used to develop a sourdough starter after the analysis of their fermentation characteristics.