Inhibitory effects of Leuconostoc mesenteroides 1RM3 isolated from narezushi, a fermented fish with rice, on Listeria monocytogenes infection to Caco-2 cells and A/J mice

Caecal fermentation, putrefaction and microbiotas in rats fed milk casein, soy protein or fish meal

To clarify the effect of soy protein (SP) and fish meal (FM), compared to milk casein (MC), on the intestinal environment, we examined caecal environment of rats fed the test diets. Four-week-old rats were fed AIN-76-based diet containing 20 %, w/w MC, SP or FM for 16 days. Caecal organic acids were analysed by HPLC. Caecal putrefactive compounds (indole, phenol, H2S and ammonia) were analysed by colorimetric assays. Caecal microflora was determined by 16S rRNA gene-DGGE and pyrosequencing with bar-coded primers targeting the bacterial 16S rRNA gene. n-Butyric and lactic acid levels were high in rats fed SP and FM, respectively. Butyrate-producing bacteria, such as Oscillibacter, and lactate-producing bacteria, such as Lactobacillus, were detected in each diet group. Also, the putrefactive compound contents were high in rats fed SP and FM. In this study, both DGGE and pyrosequencing analyses were able to evaluate the dynamics of the intestinal microbiota. The results indicate that dietary proteins can alter the intestinal environment, affecting fermentation by the intestinal microbiota and the generation of putrefactive compounds.

FLX pyrosequencing analysis of the effects of the brown-algal fermentable polysaccharides alginate and laminaran on rat cecal microbiotas

Edible brown algae are used as major food material in Far East Asian countries, particularly in South Korea and Japan. They contain fermentable dietary fibers, alginic acid (uronic acid polymer) and laminaran (β-1,3-glucan), that are fermented into organic acids by intestinal bacteria. To clarify the effect of edible algae on the intestinal environment, the cecal microbiotas of rats fed diets containing no dietary fiber (control) or 2% (wt/wt) sodium alginate or laminaran for 2 weeks were analyzed using FLX amplicon pyrosequencing with bar-coded primers targeting the bacterial 16S rRNA gene. The most abundant phylum in all groups was Firmicutes. Specifically, Allobaculum was dominant in all diet groups. In addition, Bacteroides capillosus (37.1%) was abundant in the alginate group, while Clostridium ramosum (3.14%) and Parabacteroides distasonis (1.36%) were only detected in the laminaran group. Furthermore, rats fed alginate showed simplified microbiota phylotypes compared with others. With respect to cecal chemical compounds, laminaran increased cecal organic acid levels, particularly propionic acid. Alginate increased total cecal organic acids. Cecal putrefactive compounds, such as indole, H(2)S, and phenol, were decreased by both alginate and laminaran. These results indicate that edible brown algae can alter the intestinal environment, with fermentation by intestinal microbiota.

Regulation of bacterial pathogenesis by intestinal short-chain Fatty acids

The human gut microbiota is inextricably linked to health and disease. One important function of the commensal organisms living in the intestine is to provide colonization resistance against invading enteric pathogens. Because of the complex nature of the interaction between the microbiota and its host, multiple mechanisms likely contribute to resistance. In this review, we dissect the biological role of short-chain fatty acids (SCFA), which are fermentation end products of the intestinal microbiota, in host-pathogen interactions. SCFA exert an extensive influence on host physiology through nutritional, regulatory, and immunomodulatory functions and can also affect bacterial fitness as a form of acid stress. Moreover, SCFA act as a signal for virulence gene regulation in common enteric pathogens. Taken together, these studies highlight the importance of the chemical environment where the biology of the host, the microbiota, and the pathogen intersects, which provides a basis for designing effective infection prevention and control.

Probiotic mechanisms of action

Probiotics are live microorganisms that provide health benefits to the host when ingested in adequate amounts. The strains most frequently used as probiotics include lactic acid bacteria and bifidobacteria. Probiotics have demonstrated significant potential as therapeutic options for a variety of diseases, but the mechanisms responsible for these effects have not been fully elucidated yet. Several important mechanisms underlying the antagonistic effects of probiotics on various microorganisms include the following: modification of the gut microbiota, competitive adherence to the mucosa and epithelium, strengthening of the gut epithelial barrier and modulation of the immune system to convey an advantage to the host. Accumulating evidence demonstrates that probiotics communicate with the host by pattern recognition receptors, such as toll-like receptors and nucleotide-binding oligomerization domain-containing protein-like receptors, which modulate key signaling pathways, such as nuclear factor-ĸB and mitogen-activated protein kinase, to enhance or suppress activation and influence downstream pathways. This recognition is crucial for eliciting measured antimicrobial responses with minimal inflammatory tissue damage. A clear understanding of these mechanisms will allow for appropriate probiotic strain selection for specific applications and may uncover novel probiotic functions. The goal of this systematic review was to explore probiotic modes of action focusing on how gut microbes influence the host.

Effects of holdfast of Laminaria japonica on listeria invasion on enterocyte-like Caco-2 cells and NO production of macrophage RAW 264.7 cells

Listeria monocytogenes (Lm) causes food poisoning in humans mainly through consumption of ready-to-eat foods. Immunocompromised persons are at the highest risk for infection. We investigated effects of crude soluble polysaccharides (SPS) and ethanolic extract (EE) fractions of frond (kombu) and holdfast (ganiashi) parts of Laminaria japonica on Lm invasion into human enterocyte-like Caco-2 cells and immune and/or inflammatory reactions of murine macrophage RAW 264.7 cells. Recovery and viscosity were high in kombu SPS. Total phenolic content and antioxidant activities (2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity and Fe-reducing power) were higher in ganiashi EE. EE of ganiashi, rather than kombu, suppressed the Lm invasion into the differentiated Caco-2 cells, though the inhibitory effect of SPS was not significant. Ganiashi SPS increased the nitric oxide (NO) production of intact RAW 264.7 cells. On the other hand, the NO production from Escherichia coli O111 lipopolysaccharide-activated cells was suppressed by kombu SPS and ganiashi EE. These results suggest that L. japonica, particularly ganiashi, might suppress the invasion and infection of Lm and also the inflammation.