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Lactic acid bacteria (LAB) are commonly used probiotics that improve human health in various aspects. We previously reported that yogurt starter strains, Lactobacillus delbrueckii subsp. bulgaricus 2038 and Streptococcus thermophilus 1131, potentially enhance the intestinal epithelial barrier function by inducing the expression of antimicrobial peptides in the small intestine. However, their effects on physical barrier functions remain unknown. In this study, we found that both strains ameliorated the decreased trans-epithelial resistance and the increased permeability of fluorescein isothiocyanate-dextran induced by tumor necrosis factor (TNF)-α and interferon (IFN)-γ in Caco-2 cells. We also demonstrated that LAB prevented a decrease in the expression and disassembly of tight junctions (TJs) induced by TNF-α and IFN-γ. To assess the repair activity of TJs, a calcium switch assay was performed. Both strains were found to promote the reassembly of TJs, and their activity was canceled by the inhibitor of AMP-activated protein kinase (AMPK). Moreover, these strains showed increased AMPK phosphorylation. These observations suggest that the strains ameliorated physical barrier dysfunction via the activation of AMPK. The activities preventing barrier destruction induced by TNF-α and IFN-γ were strain-dependent. Several strains containing L. bulgaricus 2038 and S. thermophilus 1131 significantly suppressed the barrier impairment, and L. bulgaricus 2038 showed the strongest activity among them. Our findings suggest that the intake of L. bulgaricus 2038 and S. thermophilus 1131 is a potential strategy for the prevention and repair of leaky gut. [ABSTRACT FROM AUTHOR]

Abstract \nHIGHLIGHTS Fermentation is one of the most effective methods of food preservation. Since ancient times, food has been fermented using lactic acid bacteria (LAB). Fermented milk is a very intricate fermentation ecosystem, and the microbial metabolism of fermented milk largely determines its metabolic properties. The two most frequently used dairy starter strains are Streptococcus thermophilus (S. thermophilus) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). To enhance both the culture growth rate and the flavor and quality of the fermented milk, it has long been customary to combine S. thermophilus and L. bulgaricus in milk fermentation due to their mutually beneficial and symbiotic relationship. On the one hand, the symbiotic relationship is reflected by the nutrient co-dependence of the two microbes at the metabolic level. On the other hand, more complex interaction mechanisms, such as quorum sensing between cells, are involved. This review summarizes the application of LAB in fermented dairy products and discusses the symbiotic mechanisms and interactions of milk LAB starter strains from the perspective of nutrient supply and intra- and interspecific quorum sensing. This review provides updated information and knowledge on microbial interactions in a fermented milk ecosystem.The symbiotic relationship between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is reviewed.Their nutrient co-dependence is discussed.The role of quorum sensing in their interaction is discussed for the first time.This review is of interest to colleagues interested in exploiting LAB starter cultures. [ABSTRACT FROM AUTHOR]

The rheological and physical characteristics of non-fat set yogurt produced using co-cultures of ropy EPS-producingStreptococcus thermophilusS3.3 andLactobacillus delbrueckiisubsp.bulgaricusLTM and ofStreptococcus thermophilusS3.3 andLactobacillus delbrueckiisubsp.bulgaricusH+-ATPase-defective mutant L6 under different conditions were studied. Yogurts produced with mutant L6 had a higher pH and water-holding capacity and better textural properties compared to those produced with the LTM strain. The highest storage modulus (G′) and thixotropic loops were found for yogurt made with L6 at 42°C on day 21 of cold storage. This yogurt contained a network of thick, continuous protein aggregates and large void spaces. [ABSTRACT FROM AUTHOR]

Yogurt is a fermented milk product produced by two homofermentative lactic acid bacteria,Lactobacillus delbrueckiisubsp.bulgaricusandStreptococcus thermophilus. It is consumed throughout the world as a healthy, nutritional food. In this study, the strains ofLactobacillusandStreptococcuswere isolated from raw milk samples collected from different local geographical regions of Turkey. One hundred and thirty isolates were characterized to genus level by classical morphological, physiological and biochemical tests. Twenty six of all isolates were identified asL. delbrueckiisubsp.bulgaricusand 47 isolates were identified asS. thermophilususing API 50 CHL system. RAPD-PCR was used to explain molecular characterization and genetic differentiation of a total of 73 strains. The whole cell protein profiles of these strains were tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In this study, all strains were identified by the RAPD-PCR technique to species or strain level. SDS-PAGE was also shown to be an effective method for molecular differentiation all of the strains. Phenotypic identification, RAPD-PCR and SDS-PAGE proved to be informative methods suitable to explain molecular characterization and genetic differentiation ofL. delbrueckiisubsp.bulgaricusandS. thermophilusstrains isolated from raw milk. In the present study, we described an identification system by using RAPD-PCR and SDS-PAGE techniques and used this system for genetic differentiation ofL. delbrueckiisubsp. bulgaricus andS. thermophilusstrains isolated from raw milk. It is believed that these two molecular techniques allow researchers to fill the significant gaps present in our understanding of these organisms by providing a comprehensive view potentially involved in industrially relevant phenotypes from different geographical origin. [ABSTRACT FROM AUTHOR]

In order to purify proteinase fromLactobacillus delbrueckiisubsp.bulgaricus, chromatography methods including ion-exchange and hydrophobic interaction were combined. Chromatographic conditions were structured and optimized. The final sample volume, flow rate, and length of gradient for anion exchange chromatography were 20 mL, 5 mL/min and 10 column volume length of gradient, in that order. Besides, the flow rate and length of gradient for hydrophobic interaction chromatography were 1 mL/min and 10 column volume. Proteinase was purified up to 43-fold with a specific activity of 54.4 U/mg protein, and the recovery of 46.6%. The molecular weight of the purified proteinase was about 40 kDa. [ABSTRACT FROM PUBLISHER]

Yogurt is a fermented milk product produced by two homofermentative lactic acid bacteria, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. It is consumed throughout the world as a healthy, nutritional food. In this study, the strains of Lactobacillus and Streptococcus were isolated from raw milk samples collected from different local geographical regions of Turkey. One hundred and thirty isolates were characterized to genus level by classical morphological, physiological and biochemical tests. Twenty six of all isolates were identified as L. delbrueckii subsp. bulgaricus and 47 isolates were identified as S. thermophilus using API 50 CHL system. RAPD-PCR was used to explain molecular characterization and genetic differentiation of a total of 73 strains. The whole cell protein profiles of these strains were tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In this study, all strains were identified by the RAPD-PCR technique to species or strain level. SDS-PAGE was also shown to be an effective method for molecular differentiation all of the strains. Phenotypic identification, RAPD-PCR and SDS-PAGE proved to be informative methods suitable to explain molecular characterization and genetic differentiation of L. delbrueckii subsp. bulgaricus and S. thermophilus strains isolated from raw milk. In the present study, we described an identification system by using RAPD-PCR and SDS-PAGE techniques and used this system for genetic differentiation ofL. delbrueckii subsp. bulgaricus and S. thermophilus strains isolated from raw milk. It is believed that these two molecular techniques allow researchers to fill the significant gaps present in our understanding of these organisms by providing a comprehensive view potentially involved in industrially relevant phenotypes from different geographical origin. [ABSTRACT FROM AUTHOR]

Superior artisanal isolates of thermophilic lactic acid bacteria producing high lactic acid and β-galactosidase were isolated from traditional Turkish yogurt samples from the Toros mountain region from a highly bio-diverse environment. A full factorial statistical design, with the factors of types of strains and medium formulations under static and agitation conditions, were applied to investigate the effects on β-galactosidase and lactic acid production. Streptococcus thermophilus 95/2 and Lactobacillus delbrueckii subsp. thermophilus 77 exhibited remarkable potential as promising starter culture candidates valuable to various applications in the dairy industry. The efficiency of cell disruption methods was investigated on the extraction of intracellular β-galactosidase enzyme. Lysozyme enzyme treatment was determined as the most effective method, which resulted in approximately 1.5 and 10 times higher enzyme activity than glass bead and homogenization treatment, respectively. [ABSTRACT FROM AUTHOR]