Analysis of the complete genome sequence of Lactobacillus delbrueckii ssp. bulgaricus with post-acidification capacity and its influence on yogurt in storage.

In recent years, yogurt has been one of the most popular fermented dairy products and is sold worldwide. In this study, pH and titrated acid changes of 4 strains of Lactobacillus delbrueckii ssp. bulgaricus fermented milk during storage were detected. The difference between L. bulgaricus KLDS1.1011 and KLDS1.0207 was significant, with the latter exhibiting reduced acidity levels. Therefore, we determined the complete genome sequence of the 2 strains. Then the expression of specific genes and common genes related to glucose metabolism and proteolysis of L. bulgaricus KLDS1.1011 and KLDS1.0207 were detected by quantitative real-time reverse-transcription PCR. Analysis indicated that the key enzymes in glycometabolism and proteolysis of L. bulgaricus KLDS1.1011 were significantly different than those of L. bulgaricus KLDS1.0207. The contents of lactose and glucose decreased during storage of L. bulgaricus fermented milk, as determined by HPLC, and the contents of lactic acid and galactose increased, with L. bulgaricus KLDS1.1011 increasing less. With skim milk as a raw material, L. bulgaricus KLDS1.1011, KLDS1.0207, and Streptococcus thermophilus S1 were used as fermentation strains to yield yogurt at 42°C, and sensory evaluation was compared with yogurt fermented by commercial starter cultures. Yogurt from L. bulgaricus KLDS1.1011 was the highest-rated. Therefore, the study may provide guidelines for the development of yogurt starters.

Bifidobacterium longum K5 Prevents Enterohaemorrhagic Escherichia coli O157:H7 Infection in Mice through the Modulation of the Gut Microbiota.

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is a commonly encountered foodborne pathogen that can cause hemorrhagic enteritis and lead to hemolytic uremic syndrome (HUS) in severe cases. Bifidobacterium is a beneficial bacterium that naturally exists in the human gut and plays a vital role in maintaining a healthy balance in the gut microbiota. This study investigated the protective effects of B. longum K5 in a mouse model of EHEC O157:H7 infection. The results indicated that pretreatment with B. longum K5 mitigated the clinical symptoms of EHEC O157:H7 infection and attenuated the increase in myeloperoxidase (MPO) activity in the colon of the mice. In comparison to the model group, elevated serum D-lactic acid concentrations and diamine oxidase (DAO) levels were prevented in the K5-EHEC group of mice. The reduced mRNA expression of tight junction proteins (ZO-1, Occludin, and Claudin-1) and mucin MUC2, as well as the elevated expression of virulence factors Stx1A and Stx2A, was alleviated in the colon of both the K5-PBS and K5-EHEC groups. Additionally, the increase in the inflammatory cytokine levels of TNF-α and IL-1ß was inhibited and the production of IL-4 and IL-10 was promoted in the K5-EHEC group compared with the model group. B. longum K5 significantly prevented the reduction in the abundance and diversity of mouse gut microorganisms induced by EHEC O157:H7 infection, including blocking the decrease in the relative abundance of Roseburia, Lactobacillus, and Oscillibacter. Meanwhile, the intervention with B. longum K5 promoted the production of acetic acid and butyric acid in the gut. This study provides insights into the use of B. longum K5 for developing probiotic formulations to prevent intestinal diseases caused by pathogenic bacterial infections.

Bifidobacterium bifidum E3 Combined with Bifidobacterium longum subsp. infantis E4 Improves LPS-Induced Intestinal Injury by Inhibiting the TLR4/NF-κB and MAPK Signaling Pathways In Vivo.

Changes in the functions of the intestinal barrier occur in parallel with the development of sepsis. The protection by Bifidobacterium strains (BB, BL, BB12, and BLBB) was evaluated in mice injected with lipopolysaccharide (LPS). The results revealed an increase in the ratio of ileal villus length to crypt depth in the BLBB group compared with that in the LPS group, as were the number of IgA+ plasma, CD4+/CD8+ T, and dendritic cells. The levels of diamine oxidase (DAO) and d-lactic acid in the serum were lessened in the BLBB group after LPS injection compared with that in the LPS group. In addition, the BLBB group exhibited an increased expression level of tight junction proteins (zonula occludens-1, occludin, and claudin-1), mucin (MUC2) mRNA, reduced NFκB/MAPK signaling pathways, and decreased expression levels of inflammatory cytokines (IL-1ß, IL-6, and TNF-α). The BLBB group enriched the relative abundance of Muribaculaceae, Lachnospiraceae_NK4A136_group, Clostridia_Ucg-014, and Alistipes, resulting in an increase in strains producing short-chain fatty acids. Furthermore, the BLBB group leads to higher levels of deoxycholic acid and biosynthesized linoleate. This study suggested that the BLBB group could enhance the capacity of the intestinal barrier and intestinal mucosal immunity, reduce intestinal inflammation, and improve the composition of gut microbiota. Bifidobacterium bifidum E3 combined with Bifidobacterium longum subsp. infantis E4 may thus serve as a probiotic against the intestinal injury caused by LPS.

Human milk and infant formula modulate the intestinal microbiota and immune systems of human microbiota-associated mice.

Many infants on an exclusive breastfeeding regimen are often fed inadequate amounts, and this creates an imbalance between the overall effects of breast milk and commercial infant formulas. We comparatively analyzed the impact of human milk and two infant formulas in modulating the intestinal microbiota and the immune systems of mice colonized by healthy infant feces. The results showed that compared to infant formula, human milk decreased the levels of alanine transaminase, alkaline phosphatase, and total protein. Also, it improved the immune system through the level of cytokines (CD4+ lymphocytes, Th1, Th2, Th17, and Treg cells) and immunity indicators (IL-2, IL-4, IL-9, and sIgA). Human milk decreased intestinal mucosal permeability compared to infant formula. Bacterial 16S rRNA gene sequence analysis revealed that human milk increased the abundance of Akkermansia and Bacteroides, while infant formula increased the abundance of Lactobacillus and Escherichia_Shigella. Collectively, our results showed that human milk is more suitable for infants than the two commercial infant formulas based on intestinal microbiota and immune system analyses. These findings thus support a theoretical basis for the development of infant formulas.