Short-chain fatty acids and polyamines in the pathogenesis of necrotizing enterocolitis: Kinetics aspects in gnotobiotic quails

Despite years of investigation, pathogenesis of necrotizing enterocolitis (NEC) remains elusive. Bacterial metabolites were implicated by several authors but their roles remain controversial. The aim of our study was to investigate the role of SCFAs and polyamines through a kinetic study of histological and macroscopical digestive lesions in monobiotic quails. Germ-free quails, inoculated with a Clostridium butyricum strain involved in a NEC case, were fed or not with a diet including lactose (7%). Quails were sacrificed at various times between D7 and D24 after bacterial inoculation. NEC-like lesions, i.e. thickening, pneumatosis, and hemorrhages, occurred only in lactose-fed quails and increased with time. The main histological characteristics were infiltrates of mononuclear cells, then heterophilic cells, then gas cyst and necrosis. The first event observed, before histological and macroscopical lesions, is a high production of butyric acid, which precedes an increase of iNOS gene expression. No difference in polyamines contents depending on the diet was observed. These results show the major role of butyric acid produced by commensal bacteria in the onset of the digestive lesions.     

Diversity of gut Bifidobacterium species is not altered between allergic and non-allergic French infants

Some clinical studies have suggested a relationship between allergic diseases and gut microbiota. We aimed to study bifidobacterial colonization at species and strain levels in ten allergic French infants included at their first clinical consultation and 20 controls matching for age at sampling, mode of delivery, per partum antibiotics, type of feeding and antibiotics in the first weeks of life. The faecal microbiota was analyzed by culture methods and TTGE. Bifidobacterial species and strains were identified using multiplex PCR and Box-PCR fingerprinting. No differences were observed between groups in the number of colonized infants or in the levels of colonization by the main aerobic and anaerobic genera. All infants were colonized with high levels of Bifidobacterium except for one in each group. One to 5 Bifidobacterium species and 1 to 7 strains were observed per subject independently of allergic status and age at sampling. Our study showed the infants to be colonized by several species and strains, including several strains from the same species. This diversity in Bifidobacterium colonization was not related with the allergic status and showed that the link between Bifidobacterium colonization and allergic diseases is complex and cannot be restricted to the role attributed to Bifidobacterium species.     

Gnotobiotic Mouse Immune Response Induced by Bifidobacterium sp. Strains Isolated from Infants

Bifidobacterium, which is a dominant genus in infants’ fecal flora and can be used as a probiotic, has shown beneficial effects in various pathologies, including allergic diseases, but its role in immunity has so far been little known. Numerous studies have shown the crucial role of the initial intestinal colonization in the development of the intestinal immune system, and bifidobacteria could play a major role in this process. For a better understanding of the effect of Bifidobacterium on the immune system, we aimed at determining the impact of Bifidobacterium on the T-helper 1 (T_H1)/T_H2 balance by using gnotobiotic mice. Germfree mice were inoculated with Bifidobacterium longum NCC2705, whose genome is sequenced, and with nine Bifidobacterium strains isolated from infants’ fecal flora. Five days after inoculation, mice were killed. Transforming growth factor β1 (TGF-β1), interleukin-4 (IL-4), IL-10, and gamma interferon (IFN-γ) gene expressions in the ileum and IFN-γ, tumor necrosis factor alpha (TNF-α), IL-10, IL-4, and IL-5 secretions by splenocytes cultivated for 48 h with concanavalin A were quantified. Two Bifidobacterium species had no effect (B. adolescentis) or little effect (B. breve) on the immune system. Bifidobacterium bifidum, Bifidobacterium dentium, and one B. longum strain induced T_H1 and T_H2 cytokines at the systemic and intestinal levels. One B. longum strain induced a T_H2 orientation with high levels of IL-4 and IL-10, both secreted by splenocytes, and of TGF-β gene expression in the ileum. The other two strains induced T_H1 orientations with high levels of IFN-γ and TNF-α splenocyte secretions. Bifidobacterium's capacity to stimulate immunity is species specific, but its influence on the orientation of the immune system is strain specific.     

New selective medium for selection of bifidobacteria from human feces

This work reports an alternative selective medium for reliable and efficient isolation of human fecal bifidobacteria. It uses a base commercially available, does not need pH adjustment and can be autoclaved with its additives. It provides a useful alternative for fecal bifidobacteria isolation.     

Infant gut microbiota is protective against cow's milk allergy in mice despite immature ileal T-cell response

Faecal microbiota of healthy infant displays a large abundance of Bifidobacterium spp. and Bacteroides spp. Although some studies have reported an association between these two genera and allergy, these findings remain a subject of debate. Using a gnotobiotic mouse model of cow's milk allergy, we investigated the impact of an infant gut microbiota – mainly composed of Bifidobacterium and Bacteroides spp. – on immune activation and allergic manifestations. The transplanted microbiota failed to restore an ileal T-cell response similar to the one observed in conventional mice. This may be due to the low bacterial translocation into Peyer's patches in gnotobiotic mice. The allergic response was then monitored in germ-free, gnotobiotic, and conventional mice after repeated oral sensitization with whey proteins and cholera toxin. Colonized mice displayed a lower drop of rectal temperature upon oral challenge with b-lactoglobulin, lower plasma mMCP-1, and lower anti-BLG IgG1 than germ-free mice. The foxp3 gene was highly expressed in the ileum of both colonized mice that were protected against allergy. This study is the first demonstration that a transplanted healthy infant microbiota mainly composed of Bifidobacterium and Bacteroides had a protective impact on sensitization and food allergy in mice despite altered T-cell response in the ileum.     

Protective effect of post-ischemic treatment with trans-resveratrol on cytokine production and neutrophil recruitment by rat liver

Oxidative and inflammatory processes are elicited during hepatic post-ischemic reperfusion and generate liver damage. This study investigated the early anti-inflammatory effect of trans-resveratrol (T-res) and its consequences on the late self-aggravating inflammatory process in liver ischemia-reperfusion (I/R). Partial hepatic ischemia was initiated in rats for 1 h and T-res (0.02 and 0.2 mg/kg) was administered intravenously 5 min before starting reperfusion for 3 h. Plasma levels of aminotransferases and cytokines (tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6) and hepatic neutrophil recruitment were assessed. Hepatic expression of stress protein (heat-shock protein (HSP-70), heme oxygenase-1(HO-1)) and cytokine (TNF-α, IL-1β, keratinocyte chemoattractant (KC)) mRNA was investigated. I/R caused an increase in aminotransferase levels and increased polymorphonuclear cell infiltration. Post-ischemic treatment with T-res (0.02 and 0.2 mg/kg) resulted in a significant decrease in aminotransferase, IL-1β and IL-6 plasma levels by about 40%, 60% and 40%, respectively, compared to the vehicle I/R group. Post-ischemic treatment with T-res (0.02 mg/kg) also significantly decreased hepatic neutrophil recruitment. TNF-α, IL-1β, KC and HO-1 hepatic mRNA expression was reduced by T-res without any change in HSP-70 mRNA. This T-res mediated decrease in early release of cytokines and neutrophil recruitment led to a reduction in the late inflammatory process. T-resveratrol might be useful in the prevention of inflammation secondary to hepatic surgery or liver transplantation.     

Germ-free status and altered caecal subdominant microbiota are associated with a high susceptibility to cow's milk allergy in mice

Studies suggesting that the development of atopy is linked to gut microbiota composition are inconclusive on whether dysbiosis precedes or arises from allergic symptoms. Using a mouse model of cow's milk allergy, we aimed at investigating the link between the intestinal microbiota, allergic sensitization, and the severity of symptoms. Germ-free and conventional mice were orally sensitized with whey proteins and cholera toxin, and then orally challenged with β-lactoglobulin (BLG). Allergic responses were monitored with clinical symptoms, plasma markers of sensitization, and the T-helper Th1/Th2/regulatory-T-cell balance. Microbiota compositions were analysed using denaturing gradient gel electrophoresis and culture methods. Germ-free mice were found to be more responsive than conventional mice to sensitization, displaying a greater reduction of rectal temperature upon challenge, higher levels of blood mouse mast cell protease-1 (mMCP-1) and BLG-specific immunoglobulin G1 (IgG1), and a systemic Th2-skewed response. This may be explained by a high susceptibility to release mMCP-1 even in the presence of low levels of IgE. Sensitization did not alter the microbiota composition. However, the absence of or low Staphylococcus colonization in the caecum was associated with high allergic manifestations. This work demonstrates that intestinal colonization protects against oral sensitization and allergic response. This is the first study to show a relationship between alterations within the subdominant microbiota and severity of food allergy.     

Clostridium difficile Cell Attachment Is Modified by Environmental Factors

Adherence of Clostridium difficile to Vero cells under anaerobic conditions was increased by a high sodium concentration, calcium-rich medium, an acidic pH, and iron starvation. The level of adhesion of nontoxigenic strains was comparable to that of toxigenic strains. Depending on the bacterial culture conditions, Vero cells could bind to one, two, or three bacterial surface proteins with molecular masses of 70, 50, and 40 kDa.