Aging is commonly associated with chronic oxidative stress and mild inflammation that can cause a variety of degenerative diseases. Lactic acid bacteria (LAB) provide several health benefits to the host including antioxidant activity and immune system regulation. However, there is a lack of information regarding the antioxidant mechanisms of probiotics in vivo. Therefore, the aim of this study was to elucidate the possible mechanisms for the preventive effect of LAB on aging. First, 25 LAB strains were screened for finding potential probiotics with high antioxidant capacity using in vitro methods. Second, D-galactose was administered by subcutaneous injection once daily for 8 weeks to establish an aging mouse model to investigate the protective effects and underlying mechanisms of the potential probiotic strain Lactobacillus helveticus KLDS1.8701, identified from the screening. The results in vitro showed that L. helveticus KLDS1.8701 had a better property with remarkable free radical scavenging activity. In vivo, L. helveticus KLDS1.8701 supplementation significantly ameliorated aging-related changes such as decreased organic index, liver injury and increased endotoxin. L. helveticus KLDS1.8701 supplementation reduced hepatic oxidative stress by modulating the Nrf-2 pathway. Notably, L. helveticus KLDS1.8701 supplementation restored the gut microbiota composition to that of the control group, resulting in increased butyrate production and decreased endotoxin production. These findings indicated that L. helveticus KLDS1.8701 supplementation manipulated gut microbiota and its metabolites could attenuate hepatic oxidative stress via the gut–liver axis.

Correlations between oxidative stress and degenerative diseases have been gaining increasing attention. A number of studies affirm that exopolysaccharide (EPS) produced by lactic acid bacteria (LAB) can alleviate oxidative stress and further prevent the related diseases. In our previous study, Lactobacillus helveticus KLDS1.8701 has been shown to possess high antioxidant capacity in vitro. The aim of this study was to evaluate the ameliorative effects of EPS produced by L. helveticus KLDS1.8701 on oxidative stress. Firstly, EPS was isolated from the culture of L. helveticus KLDS1.8701 and purified using DEAE-Sepharose Fast Flow chromatography. Secondly, the antioxidant capacities of EPS fractions were evaluated using in vitro methods. Thirdly, an in vivo study was performed to investigate the possible protective effects of EPS on D-galactose (D-gal)-induced liver damage and gut microbiota disorder. In vitro antioxidant activity results suggested that EPS-1 exhibited strong scavenging properties on 2,2-diphenyl-1-picrylhydrazyl radical, superoxide radical, hydroxyl radical, and chelating activity on ferrous ion. In vivo, EPS-1 supplementation significantly attenuated oxidative status such as decreased organic index, liver injury and liver oxidative stress. EPS-1 supplementation shifted the gut microbiota composition to that of the control group. In addition, the analysis of Spearman's rank correlation suggested that the protective effects of EPS correlated with manipulating the gut microbiota composition in D-gal-induced mice. These results implied that EPS-1 supplementation could mitigate hepatic oxidative stress via manipulating the gut microbiota composition and be used as a potential candidate to attenuate oxidative damage.

Inflammatory bowel disease (IBD) is a chronic immune-related disease, which can occur through the dysfunction of the immune system caused by the imbalance of gut microbiota. Previous studies have reported the beneficial effects of Bifidobacterium on colitis, while the related mechanisms behind these effects have not been fully elucidated. The aim of our study is to investigate the alleviation effect of Bifidobacterium animalis subsp. lactis XLTG11 (B. lactis) on dextran sulfate sodium (DSS)-induced colitis and its potential mechanism. The results showed that B. lactis XLTG11 significantly decreased weight loss, disease activity index score, colon shortening, myeloperoxide activity, spleen weight, and colon tissue damage. Additionally, B. lactis XLTG11 significantly decreased the levels of pro-inflammatory cytokines and increased the level of anti-inflammatory cytokine. Meanwhile, high doses of B. lactis XLTG11 significantly up-regulated the expression of tight junction proteins and inhibited activation of Toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MYD88)/nuclear factor-κB (NF-κB) signaling pathway. Furthermore, B. lactis XLTG11 increased the gut microbiota diversity and modulated gut microbiota composition caused by DSS. Moreover, Spearman’s correlation analysis also found that several specific gut microbiota were significantly correlated with colitis-related indicators. These results demonstrated that B. lactis XLTG11 can alleviate DSS-induced colitis by inhibiting the activation of the TLR4/MYD88/NF-κB signaling pathway, regulating inflammatory cytokines, improving intestinal barrier function, and modulating the gut microbiota.

Lactic acid bacteria play increasingly important roles in the food industry. Streptococcus thermophilus KLDS 3.1003 strain was isolated from traditional yogurt in Inner Mongolia, China. It has shown high antimicrobial activity against selected foodborne and vaginal pathogens. In this study, we investigated and analyzed its complete genome sequence. The S. thermophilus KLDS 3.1003 genome comprise of a 1,899,956 bp chromosome with a G+C content of 38.92%, 1,995 genes, and 6 rRNAs. With the exception of S. thermophilus M17TZA496, S. thermophilus KLDS 3.1003 has more tRNAs (amino acid coding genes) compared to some S. thermophilus strains available on the National Centre for Biotechnology Information database. MG-RAST annotation showed that this strain has 317 subsystems with most genes associated with amino acid and carbohydrate metabolism. This strain also has a unique EPS gene cluster containing 23 genes, and may be a mixed dairy starter culture. This information provides more insight into the molecular basis of its potentials for further applications in the dairy and allied industries.