Characterization and immunomodulation of Bifidobacterium Pseudocatenulatum G4 and Bifidobacterium Longum BB536 in vitro

Probiotics bacteria have fundamental and important roles in the human immune system; hence they are also called ‘’good bacteria‘’. Probiotic bacteria such as Bifidobacterium pseudocatenulatum G4 and Bifidobacterium longum BB536 are natural members of the human intestinal tract that have immonodulatory activity. They stimulate dendritic cells, peyer’s patches, lymphocytes such as B- lymphocytes, NK cells and T- cells. Thus, they inhibit the growth of pathogenic bacteria. In the first part of this study, the effect of colonic pH (5.7, 6.4 and 6.9) and the different concentration of hydrogen peroxide (H2O2) (50, and 100 µg/l) on bifidobacteria growth were evaluated. Modulation of host immunity is one of the proposed benefits of the consumption of probiotics such as Bifidobacterium pseudocatenulatum G4 and Bifidobacterium longum BB536. On the other hand, activity of the bacteria can be changed using different pH and high concentration of H2O2 which will have an inhibitory effect on bacteria growth. Also, Preparation of bifidobacteria with different method such as heat treatment and sonication can enable the active substances to be accessible to relevant lymphoid cells. In another word, exposure of the immunopotentiators may have occurred as the result of leakage of intracellular components or disruption of huge complex of cell wall materials. Two strains of B. pseudocatenulatum G4 and B. longum BB536 were examined for their survival in colonic pH. The survival rate of bifidobacteria in colonic pH did not vary among isolates. B. pseudocatenulatum G4 and B. longum BB536 maintain high viability of > 108 cfu/ml during 3 hours of incubation in the different pH solution. Hence, bifidobacteria can grow in different colonic pH (5.7, 6.4 and 6.9) with no reduction in the number of living bacterial cells as compared to the control group. The survival rate of bifidobacteria at H2O2 concentrations varied during 36 hours. The growth of two strains of bifidobacteria decreased significantly (P < 0.05) at 100 µg/ml H2O2 during 36 hours. On the other hand, these results revealed that bifidobacteria growth can be reduced by different concentration of H2O2 (50 and 100 µg/l) during 36 hours. High concentration of H2O2 causes the reduction of immune responses and the mediation of host defence. One of the most important criteria of the bifidobacteria is the ability to increase the immune system in order to increase the interleukins and cytokines. Live and heat-treated bifidobacteria were used in this study to measure cytokine production such as IL-12, IL-6, IL-4, IFN-γ and IgA after isolation of mice Peyer’s patches. Mice that were orally administered with heat-treated bacteria (B. pseudocatenulatum G4 and B. longum BB536) for seven consecutive days showed an increase in immunomodulatory responses because of the production of heat shock protein during heating process. So the bacteria can induce inflammatory cytokine by activation bacterial mechanisms by pattern-recognition receptors such as toll like receptors (TLRs) Therefore, the bifidobacteria induce more inflammatory cytokines but there are no any significant differences between these two strains of bifidobacteria. The level of IFN-γ significant increased more than other cytokines therefore, it has a stronger immunomodulatory effect (p < 0.05). This study also showed that live and heat-treated bifidobacteria might induce different immune responses by increasing the level of cytokines and immunomodulatory responses through the Peyer’s patches (PPs) activation. It is hypothesised that heattreated bacteria increase the production of cytokines and immunomodulatory effect; nonetheless, comparative studies on the immunological properties that support the selection of strains of the same species for specific health benefits are needed in future.

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