Jean-Jacques Gratadoux

Faecalibacterium prausnitzii is an anti-inflammatory commensal bacterium identified by gut microbiota analysis of Crohn disease patients

A decrease in the abundance and biodiversity of intestinal bacteria within the dominant phylum Firmicutes has been observed repeatedly in Crohn disease (CD) patients. In this study, we determined the composition of the mucosa-associated microbiota of CD patients at the time of surgical resection and 6 months later using FISH analysis. We found that a reduction of a major member of Firmicutes, Faecalibacterium prausnitzii, is associated with a higher risk of postoperative recurrence of ileal CD. A lower proportion of F. prausnitzii on resected ileal Crohn mucosa also was associated with endoscopic recurrence at 6 months. To evaluate the immunomodulatory properties of F. prausnitzii we analyzed the anti-inflammatory effects of F. prausnitzii in both in vitro (cellular models) and in vivo [2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced] colitis in mice. In Caco-2 cells transfected with a reporter gene for NF-κB activity, F. prausnitzii had no effect on IL-1β-induced NF-κB activity, whereas the supernatant abolished it. In vitro peripheral blood mononuclear cell stimulation by F. prausnitzii led to significantly lower IL-12 and IFN-γ production levels and higher secretion of IL-10. Oral administration of either live F. prausnitzii or its supernatant markedly reduced the severity of TNBS colitis and tended to correct the dysbiosis associated with TNBS colitis, as demonstrated by real-time quantitative PCR (qPCR) analysis. F. prausnitzii exhibits anti-inflammatory effects on cellular and TNBS colitis models, partly due to secreted metabolites able to block NF-κB activation and IL-8 production. These results suggest that counterbalancing dysbiosis using F. prausnitzii as a probiotic is a promising strategy in CD treatment.

A Novel Mucosal Vaccine Based on Live Lactococci Expressing E7 Antigen and IL-12 Induces Systemic and Mucosal Immune Responses and Protects Mice against Human Papillomavirus Type 16-Induced Tumors

Current strategies to prevent or treat human papillomavirus type 16 (HPV-16) infection are promising, but remain costly. More economical but efficient vaccines are thus needed. In this study, we evaluated the protective effects of mucosally coadministered live Lactococcus lactis strains expressing cell wall-anchored E7 Ag and a secreted form of IL-12 to treat HPV-16-induced tumors in a murine model. When challenged with lethal levels of tumor cell line TC-1 expressing E7, immunized mice showed full prevention of TC-1-induced tumors, even after a second challenge, suggesting that this prophylactic immunization can provide long-lasting immunity. Therapeutic immunization with L. lactis recombinant strains, i.e., 7 days after TC-1 injection, induced regression of palpable tumors in treated mice. The antitumor effects of vaccination occurred through a CTL response, which is CD4+ and CD8+ dependent. Furthermore, immunized mice developed an E7-specific mucosal immune response. These preclinical results suggest the feasibility of the low-cost mucosal vaccination and/or immunotherapy strategies against HPV-related cervical cancer in humans.

The Commensal Bacterium Faecalibacterium prausnitzii Is Protective in DNBS-induced Chronic Moderate and Severe Colitis Models

Background:The abundance of Faecalibacterium prausnitzii, an abundant and representative bacterium of Firmicutes phylum, has consistently been observed to be lower in patients with Crohns disease than in healthy individuals. We have shown that both F. prausnitzii and its culture supernatant (SN) have anti-inflammatory and protective effects in a TNBS-induced acute colitis mouse model. Here, we tested the effects of both F. prausnitzii and its SN in moderate and severe DNBS-induced chronic colitis mouse models. Methods:Colitis was induced by intrarectal administration of DNBS. After either 4 or 10 days of recovery (severe and moderate protocols, respectively), groups of mice were intragastrically administered either with F. prausnitzii A2-165 or with its culture SN for 7 or 10 days. Three days before being sacrificed, colitis was reactivated by administration of a lower dose of DNBS. The severity of colitis at the time of being sacrificed was assessed by weight loss and macroscopic and microscopic scores. Myeloperoxidase (MPO) activity, cytokine levels, lymphocyte populations, and changes in microbiota were studied. Results:Intragastric administration of either F. prausnitzii or its SN led to a significant decrease in colitis severity in both severe and moderate chronic colitis models. The lower severity of colitis was associated with down-regulation of MPO, pro-inflammatory cytokines, and T-cell levels. Conclusions:We show, for the first time, protective effects of both F. prausnitzii and its SN during both the period of recovery from chronic colitis and colitis reactivation. These results provide further evidence that F. prausnitzii is an anti-inflammatory bacterium with therapeutic potential for patients with inflammatory bowel disease.

Production of a Heterologous Nonheme Catalase by Lactobacillus casei: an Efficient Tool for Removal of H2O2 and Protection of Lactobacillus bulgaricus from Oxidative Stress in Milk

ABSTRACT Lactic acid bacteria (LAB) are generally sensitive to H2O2, a compound that they can paradoxically produce themselves, as is the case for Lactobacillus bulgaricus. Lactobacillus plantarum ATCC 14431 is one of the very few LAB strains able to degrade H2O2 through the action of a nonheme, manganese-dependent catalase (hereafter called MnKat). The MnKat gene was expressed in three catalase-deficient LAB species: L. bulgaricus ATCC 11842, Lactobacillus casei BL23, and Lactococcus lactis MG1363. While the protein could be detected in all heterologous hosts, enzyme activity was observed only in L. casei. This is probably due to the differences in the Mn contents of the cells, which are reportedly similar in L. plantarum and L. casei but at least 10- and 100-fold lower in Lactococcus lactis and L. bulgaricus, respectively. The expression of the MnKat gene in L. casei conferred enhanced oxidative stress resistance, as measured by an increase in the survival rate after exposure to H2O2, and improved long-term survival in aerated cultures. In mixtures of L. casei producing MnKat and L. bulgaricus, L. casei can eliminate H2O2 from the culture medium, thereby protecting both L. casei and L. bulgaricus from its deleterious effects.

Intragastric administration of a superoxide dismutase-producing recombinant Lactobacillus casei BL23 strain attenuates DSS colitis in mice

Human immune cells release large amounts of reactive oxygen species (ROS) such as superoxide radical and hydrogen peroxide via respiratory burst. In inflammatory bowel diseases, a sustained and abnormal activation of the immune response results in oxidative stress of the digestive tract and in a loss of intestinal homeostasis. We previously reported that heterologous production of the Lactobacillus plantarum manganese catalase (MnKat) enhances the survival of Lb. casei BL23 when exposed to oxidative stress. Anti-inflammatory effects were observed after Lb. casei BL23 oral administrations in moderate murine dextran sodium sulfate (DSS)-induced colitis, without added effects of the MnKat production. Here, we evaluated the protective effects obtained by an improved antioxidative strategy. The Lactococcus lactis sodA gene was expressed in Lb. casei BL23 which acquired an efficient manganese superoxide dismutase (MnSOD) activity. The effects of Lb. casei MnSOD alone or in combination with Lb. casei MnKat were compared first in eukaryotic cell PMA-induced oxidative stress model and then in severe murine DSS-induced colitis. Based on ROS production assays as well as colonic histological scores, a significant reduction of both oxidative stress and inflammation was observed with Lb. casei MnSOD either alone or in combination with Lb. casei MnKat. No added effect of the presence of Lb. casei MnKat was observed. These results suggest that Lb. casei BL23 MnSOD could have anti-inflammatory effects on gut inflammation.

Toll-like receptor 2 is critical for induction of Reg3β expression and intestinal clearance of Yersinia pseudotuberculosis

Objective: Yersinia pseudotuberculosis causes ileitis and mesenteric lymphadenitis by mainly invading the Peyer’s patches that are positioned in the terminal ileum. Whereas toll-like-receptor 2 (TLR2) controls mucosal inflammation by detecting certain microbiota-derived signals, its exact role in protecting Peyer’s patches against bacterial invasion has not been defined. Design: Wild-type, Tlr2-, Nod2- and MyD88-deficient animals were challenged by Y pseudotuberculosis via the oral or systemic route. The role of microbiota in conditioning Peyer’s patches against Yersinia through TLR2 was assessed by delivering, ad libitum, exogenous TLR2 agonists in drinking water to germ-free and streptomycin-treated animals. Bacterial eradication from Peyer’s patches was measured by using a colony-forming unit assay. Expression of cryptdins and the c-type lectin Reg3β was quantified by quantitative reverse transcriptase polymerase chain reaction analysis. Results: Our data demonstrated that Tlr2-deficient mice failed to limit Yersinia dissemination from the Peyer’s patches and succumbed to sepsis independently of nucleotide-binding and oligomerisation domain 2 (NOD2). Recognition of both microbiota-derived and myeloid differentiation factor 88 (MyD88)-mediated elicitors was found to be critically involved in gut protection against Yersinia-induced lethality, while TLR2 was dispensable to systemic Yersinia infection. Gene expression analyses revealed that optimal epithelial transcript level of the anti-infective Reg3β requires TLR2 activation. Consistently, Yersinia infection triggered TLR2-dependent Reg3β expression in Peyer’s patches. Importantly, oral treatment with exogenous TLR2 agonists in germ-free animals was able to further enhance Yersinia-induced expression of Reg3β and to restore intestinal resistance to Yersinia. Lastly, genetic ablation of Reg3β resulted in impaired clearance of the bacterial load in Peyer’s patches. Conclusions: TLR2/REG3β is thus an essential component in conditioning epithelial defence signalling pathways against bacterial invasion.

Isolation and identification of cheese-smear bacteria inhibitory to Listeria spp.

A newly developed hydrophobic grid membrane method was used to rapidly screen 105 traditional French cheeses for surface smear microorganisms inhibitory to Listeria monocytogenes strain V7. Approximately 125,000 colonies comprising a wide variety of bacteria were examined of which less than 0.1% produced visible zones of inhibition. Isolates possessing antilisterial activity consisted of various strains of Enterococcus faecalis, Staphylococcus xylosus, Staphylococcus warneri and coryneform bacteria, including one orange coryneform resembling Brevibacterium linens. All strains of E. faecalis and the orange coryneform that inhibited L. monocytogenes V7 exhibited strong inhibition against a panel of 21 Listeria strains comprised of L. monocytogenes (14 strains), L. innocua (two strains), L. ivanovii (two strains), L. seeligeri (two strains) and L. welshimeri (one strain). The remaining cheese isolates showed moderate to weak inhibition towards the same set of Listeria strains. Inhibitory substances produced by all strains except the orange coryneform were sensitive to one or more of five proteolytic enzymes tested and were therefore classified as bacteriocin-like inhibitory agents.

Identification of One Novel Candidate Probiotic Lactobacillus plantarum Strain Active against Influenza Virus Infection in Mice by a Large-Scale Screening

ABSTRACT In this study, we developed a large-scale screening of bacterial strains in order to identify novel candidate probiotics with immunomodulatory properties. For this, 158 strains, including a majority of lactic acid bacteria (LAB), were screened by two different cellular models: tumor necrosis factor alpha (TNF-α)-activated HT-29 cells and peripheral blood mononuclear cells (PBMCs). Different strains responsive to both models (pro- and anti-inflammatory strains) were selected, and their protective effects were tested in vivo in a murine model of influenza virus infection. Daily intragastric administrations during 10 days before and 10 days after viral challenge (100 PFU of influenza virus H1N1 strain A Puerto Rico/8/1934 [A/PR8/34]/mouse) of Lactobacillus plantarum CNRZ1997, one potentially proinflammatory probiotic strain, led to a significant improvement in mouse health by reducing weight loss, alleviating clinical symptoms, and inhibiting significantly virus proliferation in lungs. In conclusion, in this study, we have combined two cellular models to allow the screening of a large number of LAB for their immunomodulatory properties. Moreover, we identified a novel candidate probiotic strain, L. plantarum CNRZ1997, active against influenza virus infection in mice.

Faecal D/L lactate ratio is a metabolic signature of microbiota imbalance in patients with short bowel syndrome.

Our objective was to understand the functional link between the composition of faecal microbiota and the clinical characteristics of adults with short bowel syndrome (SBS). Sixteen patients suffering from type II SBS were included in the study. They displayed a total oral intake of 2661±1005 Kcal/day with superior sugar absorption (83±12%) than protein (42±13%) or fat (39±26%). These patients displayed a marked dysbiosis in faecal microbiota, with a predominance of Lactobacillus/Leuconostoc group, while Clostridium and Bacteroides were under-represented. Each patient exhibited a diverse lactic acid bacteria composition (L. delbrueckii subsp. bulgaricus, L. crispatus, L. gasseri, L. johnsonii, L. reuteri, L. mucosae), displaying specific D and L-lactate production profiles in vitro. Of 16 patients, 9/16 (56%) accumulated lactates in their faecal samples, from 2 to 110 mM of D-lactate and from 2 to 80 mM of L-lactate. The presence of lactates in faeces (56% patients) was used to define the Lactate-accumulator group (LA), while absence of faecal lactates (44% patients) defines the Non lactate-accumulator group (NLA). The LA group had a lower plasma HCO3− concentration (17.1±2.8 mM) than the NLA group (22.8±4.6 mM), indicating that LA and NLA groups are clinically relevant sub–types. Two patients, belonging to the LA group and who particularly accumulated faecal D-lactate, were at risk of D-encephalopathic reactions. Furthermore, all patients of the NLA group and those accumulating preferentially L isoform in the LA group had never developed D-acidosis. The D/L faecal lactate ratio seems to be the most relevant index for a higher D- encephalopathy risk, rather than D- and L-lactate faecal concentrations per se. Testing criteria that take into account HCO3− value, total faecal lactate and the faecal D/L lactate ratio may become useful tools for identifying SBS patients at risk for D-encephalopathy.

Influence of lipoteichoic acid D-alanylation on protein secretion in Lactococcus lactis as revealed by random mutagenesis.

ABSTRACT Lactococcus lactis, a food-grade nonpathogenic lactic acid bacterium, is a good candidate for the production of heterologous proteins of therapeutic interest. We examined host factors that affect secretion of heterologous proteins in L. lactis. Random insertional mutagenesis was performed with L. lactis strain MG1363 carrying a staphylococcal nuclease (Nuc) reporter cassette in its chromosome. This cassette encodes a fusion protein between the signal peptide of the Usp45 lactococcal protein and the mature moiety of a truncated form of Nuc (NucT). The Nuc secretion efficiency (secreted NucT versus total NucT) from this construct is low in L. lactis (∼40%). Twenty mutants affected in NucT production and/or in secretion capacity were selected and identified. In these mutants, several independent insertions mapped in the dltA gene (involved in d-alanine transfer in lipoteichoic acids) and resulted in a NucT secretion defect. Characterization of the dltA mutant phenotype with respect to NucT secretion revealed that it is involved in a late secretion stage by causing mature NucT entrapment at the cell surface.