Dissecting the respective roles of microbiota and host genetics in the susceptibility of Card9-/- mice to colitis

BACKGROUND

The etiology of inflammatory bowel disease (IBD) is unclear but involves both genetics and environmental factors, including the gut microbiota. Indeed, exacerbated activation of the gastrointestinal immune system toward the gut microbiota occurs in genetically susceptible hosts and under the influence of the environment. For instance, a majority of IBD susceptibility loci lie within genes involved in immune responses, such as caspase recruitment domain member 9 (Card9). However, the relative impacts of genotype versus microbiota on colitis susceptibility in the context of CARD9 deficiency remain unknown.

RESULTS

Card9 gene directly contributes to recovery from dextran sodium sulfate (DSS)-induced colitis by inducing the colonic expression of the cytokine IL-22 and the antimicrobial peptides Reg3β and Reg3γ independently of the microbiota. On the other hand, Card9 is required for regulating the microbiota capacity to produce AhR ligands, which leads to the production of IL-22 in the colon, promoting recovery after colitis. In addition, cross-fostering experiments showed that 5 weeks after weaning, the microbiota transmitted from the nursing mother before weaning had a stronger impact on the tryptophan metabolism of the pups than the pups' own genotype.

CONCLUSIONS

These results show the role of CARD9 and its effector IL-22 in mediating recovery from DSS-induced colitis in both microbiota-independent and microbiota-dependent manners. Card9 genotype modulates the microbiota metabolic capacity to produce AhR ligands, but this effect can be overridden by the implantation of a WT or "healthy" microbiota before weaning. It highlights the importance of the weaning reaction occurring between the immune system and microbiota for host metabolism and immune functions throughout life. A better understanding of the impact of genetics on microbiota metabolism is key to developing efficient therapeutic strategies for patients suffering from complex inflammatory disorders. Video Abstract.

Faecalibacterium prausnitzii Skews Human DC to Prime IL10-Producing T Cells Through TLR2/6/JNK Signaling and IL-10, IL-27, CD39, and IDO-1 Induction

The human colonic mucosa contains regulatory type 1-like (Tr1-like, i.e., IL-10-secreting and Foxp3-negative) T cells specific for the gut Clostridium Faecalibacterium prausnitzii (F. prausnitzii), which are both decreased in Crohn's disease patients. These data, together with the demonstration, in mice, that colonic regulatory T cells (Treg) induced by Clostridium bacteria are key players in colon homeostasis, support a similar role for F. prausnitzii-specific Treg in the human colon. Here we assessed the mechanisms whereby F. prausnitzii induces human colonic Treg. We demonstrated that F. prausnitzii, but not related Clostridia, skewed human dendritic cells to prime IL-10-secreting T cells. Accordingly, F. prausnitzii induced dendritic cells to express a unique array of potent Tr1/Treg polarizing molecules: IL-10, IL-27, CD39, IDO-1, and PDL-1 and, following TLR4 stimulation, inhibited their up-regulation of costimulation molecules as well as their production of pro-inflammatory cytokines IL-12 (p35 and p40) and TNFα. We further showed that these potent tolerogenic effects relied on F. prausnitzii-induced TLR2/6 triggering, JNK signaling and CD39 ectonucleotidase activity, which was induced by IDO-1 and IL-27. These data, together with the presence of F. prausnitzii-specific Tr1-like Treg in the human colon, point out to dendritic cells polarization by F. prausnitzii as the first described cellular mechanism whereby the microbiota composition may affect human colon homeostasis. Identification of F. prausnitzii-induced mediators involved in Tr1-like Treg induction by dendritic cells opens therapeutic avenues for the treatment of inflammatory bowel diseases.

Card9 mediates susceptibility to intestinal pathogens through microbiota modulation and control of bacterial virulence

OBJECTIVE

In association with innate and adaptive immunity, the microbiota controls the colonisation resistance against intestinal pathogens. Caspase recruitment domain 9 (CARD9), a key innate immunity gene, is required to shape a normal gut microbiota. Card9^-/- mice are more susceptible to the enteric mouse pathogen Citrobacter rodentium that mimics human infections with enteropathogenic and enterohaemorrhagic Escherichia coli. Here, we examined how CARD9 controls C. rodentium infection susceptibility through microbiota-dependent and microbiota-independent mechanisms.

DESIGN

C. rodentium infection was assessed in conventional and germ-free (GF) wild-type (WT) and Card9^-/- mice. To explore the impact of Card9^-/-microbiota in infection susceptibility, GF WT mice were colonised with WT (WT→GF) or Card9^-/- (Card9^-/- →GF) microbiota before C. rodentium infection. Microbiota composition was determined by 16S rDNA gene sequencing. Inflammation severity was determined by histology score and lipocalin level. Microbiota-host immune system interactions were assessed by quantitative PCR analysis.

RESULTS

CARD9 controls pathogen virulence in a microbiota-independent manner by supporting a specific humoral response. Higher susceptibility to C. rodentium-induced colitis was observed in Card9^-/- →GF mice. The microbiota of Card9^-/- mice failed to outcompete the monosaccharide-consuming C. rodentium, worsening the infection severity. A polysaccharide-enriched diet counteracted the ecological advantage of C. rodentium and the defective pathogen-specific antibody response in Card9^-/- mice.

CONCLUSIONS

CARD9 modulates the susceptibility to intestinal infection by controlling the pathogen virulence in a microbiota-dependent and microbiota-independent manner. Genetic susceptibility to intestinal pathogens can be overridden by diet intervention that restores humoural immunity and a competing microbiota.

Expression of CCR6 and CXCR6 by Gut-Derived CD4+/CD8α+ T-Regulatory Cells, Which Are Decreased in Blood Samples From Patients With Inflammatory Bowel Diseases

BACKGROUND & AIMS

Faecalibacterium prausnitzii, a member of the Clostridium IV group of the Firmicutes phylum that is abundant in the intestinal microbiota, has anti-inflammatory effects. The relative level of F prausnitzii is decreased in fecal samples from patients with inflammatory bowel diseases (IBDs) compared with healthy individuals. Reduced F prausnitzii was correlated with relapse of Crohn's disease after surgery. We identified, in human colonic mucosa and blood, a population of T regulatory type 1-like T regulatory (T_REG) cells that express CD4 and CD8α (DP8α T cells) and are specific for F prausnitzii. We aimed to determine whether they are altered in patients with IBD.

METHODS

We isolated DP8α T cells from human colon lamina propria and blood samples and used flow cytometry to detect markers of cells that are of colon origin. We quantified DP8α cells that express colon-specific markers in blood samples from 106 patients with IBD, 12 patients with infectious colitis, and 35 healthy donors (controls). We identified cells that respond to F prausnitzii. Cells were stimulated with anti-CD3, and their production of interleukin 10 was measured by enzyme-linked immunosorbent assay. We compared the frequency and reactivity of cells from patients vs controls using the 2-sided Student t test or 1-way analysis of variance.

RESULTS

Circulating DP8α T cells that proliferate in response to F prausnitzii express the C-C motif chemokine receptor 6 (CCR6) and C-X-C motif chemokine receptor 6 (CXCR6). These cells also have features of T_REG cells, including production of IL-10 and inhibition of T-cell proliferation via CD39 activity. The proportion of circulating CCR6⁺/CXCR6⁺ DP8α T cells was significantly reduced (P < .0001) within the total population of CD3⁺ T cells from patients with IBD compared with patients with infectious colitis or controls. A threshold of <7.875 CCR6⁺/CXCR6⁺ DP8α T cells/10,000 CD3⁺ cells discriminated patients with IBD from those with infectious colitis with 100% specificity and 72.2% sensitivity.

CONCLUSIONS

We identified a population of gut-derived T_REG cells that are reduced in blood samples from patients with IBD compared with patients with infectious colitis or controls. These cells should be studied further to determine the mechanisms of this reduction and how it might contribute to the pathogenesis of IBD and their prognostic or diagnostic value.

Functional Characterization of Novel Faecalibacterium prausnitzii Strains Isolated from Healthy Volunteers: A Step Forward in the Use of F. prausnitzii as a Next-Generation Probiotic

Faecalibacterium prausnitzii is a major member of the Firmicutes phylum and one of the most abundant bacteria in the healthy human microbiota. F. prausnitzii depletion has been reported in several intestinal disorders, and more consistently in Crohn's disease (CD) patients. Despite its importance in human health, only few microbiological studies have been performed to isolate novel F. prausnitzii strains in order to better understand the biodiversity and physiological diversity of this beneficial commensal species. In this study, we described a protocol to isolate novel F. prausnitzii strains from feces of healthy volunteers as well as a deep molecular and metabolic characterization of these isolated strains. These F. prausnitzii strains were classified in two phylogroups and three clusters according to 16S rRNA sequences and results support that they would belong to two different genomospecies or genomovars as no genome sequencing has been performed in this work. Differences in enzymes production, antibiotic resistance and immunomodulatory properties were found to be strain-dependent. So far, all F. prausnitzii isolates share some characteristic such as (i) the lack of epithelial cells adhesion, plasmids, anti-microbial, and hemolytic activity and (ii) the presence of DNAse activity. Furthermore, Short Chain Fatty Acids (SCFA) production was assessed for the novel isolates as these products influence intestinal homeostasis. Indeed, the butyrate production has been correlated to the capacity to induce IL-10, an anti-inflammatory cytokine, in peripheral blood mononuclear cells (PBMC) but not to the ability to block IL-8 secretion in TNF-α-stimulated HT-29 cells, reinforcing the hypothesis of a complex anti-inflammatory pathway driven by F. prausnitzii. Altogether, our results suggest that some F. prausnitzii strains could represent good candidates as next-generation probiotic.

CARD9 impacts colitis by altering gut microbiota metabolism of tryptophan into aryl hydrocarbon receptor ligands

Complex interactions between the host and the gut microbiota govern intestinal homeostasis but remain poorly understood. Here we reveal a relationship between gut microbiota and caspase recruitment domain family member 9 (CARD9), a susceptibility gene for inflammatory bowel disease (IBD) that functions in the immune response against microorganisms. CARD9 promotes recovery from colitis by promoting interleukin (IL)-22 production, and Card9(-/-) mice are more susceptible to colitis. The microbiota is altered in Card9(-/-) mice, and transfer of the microbiota from Card9(-/-) to wild-type, germ-free recipients increases their susceptibility to colitis. The microbiota from Card9(-/-) mice fails to metabolize tryptophan into metabolites that act as aryl hydrocarbon receptor (AHR) ligands. Intestinal inflammation is attenuated after inoculation of mice with three Lactobacillus strains capable of metabolizing tryptophan or by treatment with an AHR agonist. Reduced production of AHR ligands is also observed in the microbiota from individuals with IBD, particularly in those with CARD9 risk alleles associated with IBD. Our findings reveal that host genes affect the composition and function of the gut microbiota, altering the production of microbial metabolites and intestinal inflammation.

Microorganisms linked to inflammatory bowel disease-associated dysbiosis differentially impact host physiology in gnotobiotic mice

Studying host-microbiota interactions are fundamental to understanding the mechanisms involved in intestinal homeostasis and inflammation. In this work, we analyzed these interactions in mice that were mono-associated with six microorganisms that are representative of inflammatory bowel disease (IBD)-associated dysbiosis: the bacteria Bacteroides thetaiotaomicron, adhesive-invasive Escherichia coli (AIEC), Ruminococcus gnavus and Roseburia intestinalis; a yeast used as a probiotic drug, Saccharomyces boulardii CNCM I-745; and another yeast, Candida albicans. Extensive ex vivo analyses including colon transcriptomics, histology, immune response, bile acid metabolism and short-chain fatty acid production were studied. We showed that B. thetaiotaomicron had the highest impact on the immune system because it was almost able to recapitulate the effects of the entire conventional microbiota and notably induced Treg pathways. Furthermore, these analyses uncovered the effects of E. coli AIEC LF82 on indoleamine 2,3-dioxygenase expression and of S. boulardii CNCM I-745 on angiogenesis. These results were confirmed in vitro in human cell lines. Finally, our results suggested that R. gnavus has major effects on metabolism, and notably on tryptophan metabolism. This work therefore reveals that microorganisms with a potential role in intestinal homeostasis and inflammation have specific impacts on the host, and it suggests several tracks to follow to understand intestinal homeostasis and IBD pathogenesis better, providing new insights to identify novel therapeutic targets.

CD4CD8αα lymphocytes, a novel human regulatory T cell subset induced by colonic bacteria and deficient in patients with inflammatory bowel disease

Gut bacterium Faecalibacterium prausnitzii activates a newly identified set of human IL-10-producing Treg cells (CD4CD8αα lymphocytes), revealing a mechanism by which commensal microbes contribute to host immunity.

How the microbiota affects health and disease is a crucial question. In mice, gut Clostridium bacteria are potent inducers of colonic interleukin (IL)-10-producing Foxp3 regulatory T cells (Treg), which play key roles in the prevention of colitis and in systemic immunity. In humans, although gut microbiota dysbiosis is associated with immune disorders, the underlying mechanism remains unknown. In contrast with mice, the contribution of Foxp3 Treg in colitis prevention has been questioned, suggesting that other compensatory regulatory cells or mechanisms may exist. Here we addressed the regulatory role of the CD4CD8 T cells whose presence had been reported in the intestinal mucosa and blood. Using colonic lamina propria lymphocytes (LPL) and peripheral blood lymphocytes (PBL) from healthy individuals, and those with colon cancer and irritable bowel disease (IBD), we demonstrated that CD4CD8αα (DP8α) T lymphocytes expressed most of the regulatory markers and functions of Foxp3 Treg and secreted IL-10. Strikingly, DP8α LPL and PBL exhibited a highly skewed repertoire toward the recognition of Faecalibacterium prausnitzii, a major Clostridium species of the human gut microbiota, which is decreased in patients with IBD. Furthermore, the frequencies of DP8α PBL and colonic LPL were lower in patients with IBD than in healthy donors and in the healthy mucosa of patients with colon cancer, respectively. Moreover, PBL and LPL from most patients with active IBD failed to respond to F. prausnitzii in contrast to PBL and LPL from patients in remission and/or healthy donors. These data (i) uncover a Clostridium-specific IL-10-secreting Treg subset present in the human colonic LP and blood, (ii) identify F. prausnitzii as a major inducer of these Treg, (iii) argue that these cells contribute to the control or prevention of colitis, opening new diagnostic and therapeutic strategies for IBD, and (iv) provide new tools to address the systemic impact of both these Treg and the intestinal microbiota on the human immune homeostasis.

It has become evident that bacteria in our gut affect health and disease, but less is known about how they do this. Recent studies in mice showed that gut Clostridium bacteria and their metabolites can activate regulatory T cells (Treg) that in turn mediate tolerance to signals that would ordinarily cause inflammation. In this study we identify a subset of human T lymphocytes, designated CD4CD8αα T cells that are present in the surface lining of the colon and in the blood. We demonstrate Treg activity and show these cells to be activated by microbiota; we identify F. prausnitzii, a core Clostridium strain of the human gut microbiota, as a major inducer of these Treg cells. Interestingly, there are fewer F. prausnitzii in individuals suffering from inflammatory bowel disease (IBD), and accordingly the CD4CD8αα T cells are decreased in the blood and gut of patients with IBD. We argue that CD4CD8αα colonic Treg probably help control or prevent IBD. These data open the road to new diagnostic and therapeutic strategies for the management of IBD and provide new tools to address the impact of the intestinal microbiota on the human immune system.

Ecology and metabolism of the beneficial intestinal commensal bacterium Faecalibacterium prausnitzii

Faecalibacterium prausnitzii is a major commensal bacterium, and its prevalence is often decreased in conditions of intestinal dysbiosis. The phylogenic identity of this bacterium was described only recently. It is still poorly characterized, and its specific growth requirements in the human gastrointestinal tract are not known. In this review, we consider F. prausnitzii metabolism, its ecophysiology in both humans and animals, and the effects of drugs and nutrition on its population. We list important questions about this beneficial and ubiquitous commensal bacterium that it would be valuable to answer.

Bacteroides thetaiotaomicron and Faecalibacterium prausnitzii influence the production of mucus glycans and the development of goblet cells in the colonic epithelium of a gnotobiotic model rodent

Background

The intestinal mucus layer plays a key role in the maintenance of host-microbiota homeostasis. To document the crosstalk between the host and microbiota, we used gnotobiotic models to study the influence of two major commensal bacteria, Bacteroides thetaiotaomicron and Faecalibacterium prausnitzii, on this intestinal mucus layer. B. thetaiotaomicron is known to use polysaccharides from mucus, but its effect on goblet cells has not been addressed so far. F. prausnitzii is of particular physiological importance because it can be considered as a sensor and a marker of human health. We determined whether B. thetaiotaomicron affected goblet cell differentiation, mucin synthesis and glycosylation in the colonic epithelium. We then investigated how F. prausnitzii influenced the colonic epithelial responses to B. thetaiotaomicron.

Results

B. thetaiotaomicron, an acetate producer, increased goblet cell differentiation, expression of mucus-related genes and the ratio of sialylated to sulfated mucins in mono-associated rats. B. thetaiotaomicron, therefore, stimulates the secretory lineage, favoring mucus production. When B. thetaiotaomicron was associated with F. prausnitzii, an acetate consumer and a butyrate producer, the effects on goblet cells and mucin glycosylation were diminished. F. prausnitzii, by attenuating the effects of B. thetaiotaomicron on mucus, may help the epithelium to maintain appropriate proportions of different cell types of the secretory lineage. Using a mucus-producing cell line, we showed that acetate up-regulated KLF4, a transcription factor involved in goblet cell differentiation.

Conclusions

B. thetaiotaomicron and F. prausnitzii, which are metabolically complementary, modulate, in vivo, the intestinal mucus barrier by modifying goblet cells and mucin glycosylation. Our study reveals the importance of the balance between two main commensal bacteria in maintaining colonic epithelial homeostasis via their respective effects on mucus.

Connecting dysbiosis, bile-acid dysmetabolism and gut inflammation in inflammatory bowel diseases

OBJECTIVE

Gut microbiota metabolises bile acids (BA). As dysbiosis has been reported in inflammatory bowel diseases (IBD), we aim to investigate the impact of IBD-associated dysbiosis on BA metabolism and its influence on the epithelial cell inflammation response.

DESIGN

Faecal and serum BA rates, expressed as a proportion of total BA, were assessed by high-performance liquid chromatography tandem mass spectrometry in colonic IBD patients (42) and healthy subjects (29). The faecal microbiota composition was assessed by quantitative real-time PCR. Using BA profiles and microbiota composition, cluster formation between groups was generated by ranking models. The faecal BA profiles in germ-free and conventional mice were compared. Direct enzymatic activities of BA biotransformation were measured in faeces. The impact of BA on the inflammatory response was investigated in vitro using Caco-2 cells stimulated by IL-1β.

RESULTS

IBD-associated dysbiosis was characterised by a decrease in the ratio between Faecalibacterium prausntizii and Escherichia coli. Faecal-conjugated BA rates were significantly higher in active IBD, whereas, secondary BA rates were significantly lower. Interestingly, active IBD patients exhibited higher levels of faecal 3-OH-sulphated BA. The deconjugation, transformation and desulphation activities of the microbiota were impaired in IBD patients. In vitro, secondary BA exerted anti-inflammatory effects, but sulphation of secondary BAs abolished their anti-inflammatory properties.

CONCLUSIONS

Impaired microbiota enzymatic activity observed in IBD-associated dysbiosis leads to modifications in the luminal BA pool composition. Altered BA transformation in the gut lumen can erase the anti-inflammatory effects of some BA species on gut epithelial cells and could participate in the chronic inflammation loop of IBD.

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.

Microbiota matures colonic epithelium through a coordinated induction of cell cycle-related proteins in gnotobiotic rat

Previous studies have suggested that intestinal microbiota modulates colonic epithelium renewal. The objective of our work was to study the effects of microbiota on colonic epithelium structure and cell cycle-related proteins by using gnotobiotic rats. Colonic crypts and amount of cell cycle-related proteins were compared between germ-free (GF), conventional (CV), and conventionalized rats by histochemistry and Western blot. Ki67 and proliferating cell nuclear antigen (PCNA) were used as surrogates for proliferative cells; p21(cip1) and p27(kip1) were markers of cell cycle arrest; anti- and proapoptotic proteins, Bcl2 and Bax, respectively, were also studied. We observed 40% increase of the crypt proliferative area 2 days after inoculation of GF rats with a complex microbiota. This recruitment of proliferative cells may account for the 30% increase of crypt depth observed between CV and GF rats. The hyperproliferative boost induced by microbiota was compensated by a fourfold increase of p21(cip1) and p27(kip1) involved in cell cycle arrest and a 30% drop of antiapoptotic Bcl2 protein while Bax was unchanged. Inductions of p21(cip1), p27(kip1), and PCNA protein were not paralleled by an increase of the corresponding mRNA. We also showed that p21(cip1) induction by microbiota was partially restored by Bacteroides thetaiotaomicron, Ruminococcus gnavus, and Clostridium paraputrificum. Colonization of the colon by a complex microbiota increases the crypt depth of colon epithelium. This event takes place in conjunction with a multistep process: a hyperproliferative boost accompanied by compensatory events as induction of p21(cip1) and p27(kip1) and decrease of Bcl2.

Comparative assessment of human and farm animal faecal microbiota using real-time quantitative PCR

Pollution of the environment by human and animal faecal pollution affects the safety of shellfish, drinking water and recreational beaches. To pinpoint the origin of contaminations, it is essential to define the differences between human microbiota and that of farm animals. A strategy based on real-time quantitative PCR (qPCR) assays was therefore developed and applied to compare the composition of intestinal microbiota of these two groups. Primers were designed to quantify the 16S rRNA gene from dominant and subdominant bacterial groups. TaqMan probes were defined for the qPCR technique used for dominant microbiota. Human faecal microbiota was compared with that of farm animals using faecal samples collected from rabbits, goats, horses, pigs, sheep and cows. Three dominant bacterial groups (Bacteroides/Prevotella, Clostridium coccoides and Bifidobacterium) of the human microbiota showed differential population levels in animal species. The Clostridium leptum group showed the lowest differences among human and farm animal species. Human subdominant bacterial groups were highly variable in animal species. Partial least squares regression indicated that the human microbiota could be distinguished from all farm animals studied. This culture-independent comparative assessment of the faecal microbiota between humans and farm animals will prove useful in identifying biomarkers of human and animal faecal contaminations that can be applied to microbial source tracking methods.

Clostridium difficile and Clostridium perfringens species detected in infant faecal microbiota using 16S rRNA targeted probes

Clostridium perfringens and Clostridium difficile are pathogenic clostridia potentially associated with gastrointestinal infections and allergy in infants. To enable the molecular detection and quantification of these species in the infant gut, two 16S rRNA oligonucleotide probes were developed: Cdif198 for C. difficile and Cperf191 for C. perfringens. We defined the probes in silico using the RDP sequence database. The probes were then validated using FISH combined with flow cytometry and a collection of target and non-target strains, and faecal samples inoculated with dilutions of C. difficile and C. perfringens strains. These new probes were used to assess the composition of the intestinal microbiota of 33 infants of 1.5 to 18.5 months of age, associated with a panel of 8 probes targeting the predominant faecal bacterial groups of humans. The probes designed allowed detection and quantification of the relative proportions of C. difficile (0.5+/-1.0%) and C. perfringens (2.1+/-2.3%) in the microbiota of infants.

Intestinal microflora and digestive toxicity of irinotecan in mice

PURPOSE

Delayed diarrhea is the most important side effect of irinotecan. The aim of this study was to investigate the role of intestinal microflora on the induction of systemic and intestinal toxicity and diarrhea, studying germ-free and holoxenic mice i.p. injected with irinotecan.

EXPERIMENTAL DESIGN

To evaluate the lethal dose, starting with 100 mg/kg/4 d, we treated the holoxenic mice with 100, 80, and 60 mg/kg/4 d and germ-free mice with 60, 80, 100, and 150 mg/kg/4 d. We recorded the percentage of dead animals, diarrhea, and the epithelial damage to the jejunum, ileum, cecum, and colon at optical and scanning electron microscopy.

RESULTS

Germ-free mice were more resistant to irinotecan than the holoxenic group. The lethal dose was between 60 and 80 mg of irinotecan for holoxenic mice and > or =150 mg for the germ-free. The intestinal damage score was higher in holoxenic than germ-free mice at 100 mg and equally diffuse in the small and large bowel. The damage in germ-free mice was less severe (8 of 40 samples) prevailing in the ileum. The differences were significant for all sites (jejunum, P < 0.001; ileum, P = 0.012; cecum, P = 0.001; colon, P < 0.001). No damage was found in germ-free mice at 60 mg. Diarrhea was present in all 100 and 80 mg holoxenic mice and in 19 of 20 cases at 60 mg whereas it was absent in 60 mg or sporadic in 80 and 100 mg germ-free mice.

CONCLUSIONS

The intestinal microflora plays a key role in the intestinal toxicity of irinotecan.

Ruminococcin A, a new lantibiotic produced by a Ruminococcus gnavus strain isolated from human feces

When cultivated in the presence of trypsin, the Ruminococcus gnavus E1 strain, isolated from a human fecal sample, was able to produce an antibacterial substance that accumulated in the supernatant. This substance, called ruminococcin A, was purified to homogeneity by reverse-phase chromatography. It was shown to be a 2,675-Da bacteriocin harboring a lanthionine structure. The utilization of Edman degradation and tandem mass spectrometry techniques, followed by DNA sequencing of part of the structural gene, allowed the identification of 21 amino acid residues. Similarity to other bacteriocins present in sequence libraries strongly suggested that ruminococcin A belonged to class IIA of the lantibiotics. The purified ruminococcin A was active against various pathogenic clostridia and bacteria phylogenetically related to R. gnavus. This is the first report on the characterization of a bacteriocin produced by a strictly anaerobic bacterium from human fecal microbiota.

Relationship between intestinal colonization of Bifidobacterium bifidum in infants and the presence of exogenous and endogenous growth-promoting factors in their stools

The relationship between the intestinal colonization of a test strain of Bifidobacterium bifidum requiring human milk growth-promoting factors in vitro and the presence of growth-promoting factors either in the stools of human neonates or in their diet was investigated. Thirty-one infants were inoculated with a single dose of this strain within the first 8 d of life. Spores of a strictly thermophilic Bacillus admixed with the B. bifidum inoculum were used as transit marker, and the fecal population levels of both strain B. bifidum and the transit marker were recorded within 6 d after inoculation. Strain B. bifidum was found in the predominant flora of six neonates. It was eliminated more quickly than the transit marker from the stools of 17 neonates. Its population remained at a low level in the remaining eight neonates. Amounts of B. bifidum growth-promoting factor in the infant stools were not significantly different whether they harbored strain B. bifidum at a high population level or not. Although these amounts were significantly higher in infants fed human milk containing B. bifidum growth-promoting factor than in infants fed formula milk without B. bifidum growth-promoting factor, strain B. bifidum became established in one of the 18 infants fed human milk and in five of the 13 formula-fed infants. No relationship could be found between the population levels of strain B. bifidum and those of facultatively anaerobic streptococci and enterobacteria already present on d 0 and 1. These results clearly show that no relationship exists between the intestinal colonization of B. bifidum and the amounts of exogenous or endogenous growth-promoting factors found in stools.

Efficiency of various bacterial suspensions derived from cecal floras of conventional chickens in reducing the population level of Salmonella typhimurium in gnotobiotic mice and chicken intestines

The antagonistic effect exerted towards Salmonella typhimurium by the flora issued from conventional chickens was studied in gnotobiotic animals. In germfree chickens and mice inoculated with S. typhimurium, the highest bacterial counts were observed in ceca, and were not significantly different in either host. The protection afforded by the inoculation of cecal flora issued from a conventional chicken was more effective when this flora was inoculated first into germfree chickens than when it was given only after inoculation with S. typhimurium. Administration of a cecal flora from a 15-day-old chick to gnotobiotic mice and chicken resulted in the inhibition of a further intestinal colonization by S. typhimurium in both hosts. Sixteen strains were isolated among the predominant populations of the fecal flora from chicken flora recipient mice. Association of 14 strains of strictly anaerobic bacteria with 2 strains of Escherichia coli and Streptococcus faecium only decreased the number of S. typhimurium in the ileum of gnotobiotic mice, but not in their cecum. Anaerobe cultures were obtained from 10(-6) and 10(-8) dilutions prepared from the fecal flora of gnotobiotic recipient mice. Antagonistic bacteria were present only in cultures from the 10(-6) dilution. Cecal concentrations of volatile fatty acids were shown not to be the sole factor implicated in the antagonistic effect against S. typhimurium.

[Seroanthropological studies of albino and melanoderm Bamiléké populations (Cameroon). ABO and Rhesus erythrocyte groups, hemoglobin S and taste sensitivity to phenylthiocarbamide]

Human oculocutaneous albinism is a recessive autosomic hereditary disease with a prevalence of 1/8,500 in bamileke tribe (Cameroon). ABO and Rhesus red blood cell group repartition, presence of hemoglobin S, taste sensitivity for phenylthiocarbamid in a group of 100 albino bamileke subjects were compared with these of 100 black bamileke subjects. There is no significant difference for these genetic markers mentionned above between albino and black bamileke subjects.

[Pathogenicity of various toxinogenic types of Clostridium perfringens administered by mouth to axenic and holoxenic mice]

Axenic mice died with signs of enterotoxaemia after oral ingestion of Clostridium perfringens type C or D. Under the same conditions, C. perfringens type B was less pathogenic, and types A and E showed no pathogenicity. The microflora of conventional mice prevented the establishment of C. perfringens types B, C and D in the digestive tract and protected them against the pathogenicity of these strains. Toxins produced in the caecum of monoxenic mice harbouring C. perfringens type C were not neutralized by the anti-C. perfringens type C antiserum. This suggests that the toxins produced in vivo by this strain were different from those produced in vitro.

[Antagonistic effect against "Clostridium perfringens" exerted in the digestive tract of gnotobiotic mice by "Clostridium" strains isolated from the microflora of conventional mice (author's transl)]

Bacterial strains isolated from the digestive tract of conventional mice produced a barrier effect against a strain of Clostridium perfringens type A (strain CP) in the gastrointestinal tract of gnotobiotic mice. This barrier effect was observed when mice, monoassociated with Escherichia coli K12, were inoculated with a mixed culture of fusiform-shaped clostridia. The collection of fusiforms (collection D) was obtained from a single colony chosen from among the 26 types studied. Collection D and E. coli K12 together exerted a barrier effect against all strains of C. perfringens type A tested. No effect was observed against a C. perfringens type C strain. The expression of the barrier effect depended on the order in which the strains were used to inoculate the mice. Thus strain CP was eliminated from the digestive tract when the mice had previously been associated with collection D and E. coli K12. If the mice were inoculated with strain CP first, however, the barrier effect was only partial. We have also been able to use two strains of clostridia (C1, C3) instead of E. coli K12 to produce a drastic barrier effect against strain CP. The order in which the strains were used to inoculate the mice did not, in this case, influence the production of a barrier effect. Three strains (Da, Db, Dc) isolated from collection D, produced only a partial barrier effect against strain CP in mice previously associated with E. coli K12. These results illustrate the difficulties encountered in determining the minimal number of bacterial strains involved in the production of a barrier effect.