Luminal Colonization Research Articles

Human neutrophil IL1β directs intestinal epithelial cell extrusion during Salmonella infection.

Infection of the human gut by Salmonella enterica Typhimurium (STM) results in a localized inflammatory disease that is not mimicked in murine infections. To determine mechanisms by which neutrophils, as early responders to bacterial challenge, direct inflammatory programming of human intestinal epithelium, we established a multi-component human intestinal organoid (HIO) model of STM infection. HIOs were micro-injected with STM and seeded with primary human polymorphonuclear leukocytes (PMN-HIOs). PMNs did not significantly alter luminal colonization of Salmonella, but their presence reduced intraepithelial bacterial burden. Adding PMNs to infected HIOs resulted in substantial accumulation of shed TUNEL+ epithelial cells that was driven by PMN Caspase-1 activity. Inhibition of Caspases-1, -3 or -4 abrogated epithelial cell death and extrusion in the infected PMN-HIOs but only Caspase-1 inhibition significantly increased bacterial burden in the PMN-HIO epithelium. Thus, PMNs promote cell death in human intestinal epithelial cells through multiple caspases as a protective response to infection. IL-1β was necessary and sufficient to induce cell shedding in the infected HIOs. These data support a critical innate immune function for human neutrophils in amplifying cell death and extrusion of human epithelial cells from the Salmonella-infected intestinal monolayer.

Vaccines Using Clostridium perfringens Sporulation Proteins Reduce Necrotic Enteritis in Chickens.

Clostridium perfringens is the prevalent enteric pathogen in humans and animals including chickens, and it remains largely elusive on the mechanism of C. perfringens-induced enteritis because of limited animal models available. In this study, we investigated the role of C. perfringens sporulation proteins as vaccine candidates in chickens to reduce necrotic enteritis (NE). C. perfringens soluble proteins of vegetative cells (CP-super1 and CP-super2) and spores (CP-spor-super1 and CP-spor-super2) were prepared, and cell and chicken experiments were conducted. We found that deoxycholic acid reduced C. perfringens invasion and sporulation using the Eimeria maxima and C. perfringens co-infection necrotic enteritis (NE) model. C. perfringens enterotoxin (CPE) was detected in the CP-spor-super1&2. CP-spor-super1 or 2 induced cell death in mouse epithelial CMT-93 and macrophage Raw 264.7 cells. CP-spor-super1 or 2 also induced inflammatory gene expression and necrosis in the Raw cells. Birds immunized with CP-spor-super1 or 2 were resistant to C. perfringens-induced severe clinical NE on histopathology and body weight gain loss. CP-spor-super1 vaccine reduced NE-induced proinflammatory Ifnγ gene expression as well as C. perfringens luminal colonization and tissue invasion in the small intestine. Together, this study showed that CP-spor-super vaccines reduced NE histopathology and productivity loss.

Characterization of the Luminal and Mucosa-Associated Microbiome along the Gastrointestinal Tract: Results from Surgically Treated Preterm Infants and a Murine Model.

Environmental factors, including nutritional habits or birth mode, are known key determinants for intestinal microbial composition. Investigations of the intestinal microbiome in different species in a multiplicity of studies during recent decades have revealed differential microbial patterns and quantities along the gastrointestinal (GI) tract. Characterization of the microbial pattern in various aspects is a prerequisite for nutritional interventions. In this 16S rRNA amplicon-based approach, we present a characterization of the mucosa-associated microbiome in comparison with the luminal community of four infants at the time of the closure of ileostomies and perform a systematic characterization of the corresponding luminal and mucosal microbiome from jejunal, ileal and colonic regions, as well as collected feces in mice. The most dominant taxa in infant-derived samples altered due to individual differences, and in the mucosa, Enterococcus, Clostridium sensu stricto 1, Veillonella, Streptococcus and Staphylococcus were the most abundant. Two less abundant taxa differed significantly between the mucosa and lumen. In murine samples, relative abundances differed significantly, mainly between the intestinal regions. Significant differences between mouse mucosa- and lumen-derived samples could be found in the observed species with a trend to lower estimated diversity in mucosa-derived samples, as well as in the relative abundance of individual taxa. In this study, we examined the difference between the mucosal and luminal bacterial colonization of the gastrointestinal tract in a small sample cohort of preterm infants. Individual differences were characterized and statistical significance was reached in two taxa (Cupriavidus, Ralstonia). The corresponding study on the different murine intestinal regions along the GI tract showed differences all over the intestinal region.

The Immature Gut Barrier and Its Importance in Establishing Immunity in Newborn Mammals.

The gut is an efficient barrier which protects against the passage of pathogenic microorganisms and potential harmful macromolecules into the body, in addition to its primary function of nutrient digestion and absorption. Contrary to the restricted macromolecular passage in adulthood, enhanced transfer takes place across the intestines during early life, due to the high endocytic capacity of the immature intestinal epithelial cells during the fetal and/or neonatal periods. The timing and extent of this enhanced endocytic capacity is dependent on animal species, with a prominent non-selective intestinal macromolecular transfer in newborn ungulates, e.g., pigs, during the first few days of life, and a selective transfer of mainly immunoglobulin G (IgG), mediated by the FcRn receptor, in suckling rodents, e.g., rats and mice. In primates, maternal IgG is transferred during fetal life via the placenta, and intestinal macromolecular transfer is largely restricted in human neonates. The period of intestinal macromolecular transmission provides passive immune protection through the transfer of IgG antibodies from an immune competent mother; and may even have extra-immune beneficial effects on organ maturation in the offspring. Moreover, intestinal transfer during the fetal/neonatal periods results in increased exposure to microbial and food antigens which are then presented to the underlying immune system, which is both naïve and immature. This likely stimulates the maturation of the immune system and shifts the response toward tolerance induction instead of activation or inflammation, as usually seen in adulthood. Ingestion of mother's milk and the dietary transition to complex food at weaning, as well as the transient changes in the gut microbiota during the neonatal period, are also involved in the resulting immune response. Any disturbances in timing and/or balance of these parallel processes, i.e., intestinal epithelial maturation, luminal microbial colonization and mucosal immune maturation due to, e.g., preterm birth, infection, antibiotic use or nutrient changes during the neonatal period, might affect the establishment of the immune system in the infant. This review will focus on how differing developmental processes in the intestinal epithelium affect the macromolecular passage in different species and the possible impact of such passage on the establishment of immunity during the critical perinatal period in young mammals.

Uncoupling of invasive bacterial mucosal immunogenicity from pathogenicity

There is the notion that infection with a virulent intestinal pathogen induces generally stronger mucosal adaptive immunity than the exposure to an avirulent strain. Whether the associated mucosal inflammation is important or redundant for effective induction of immunity is, however, still unclear. Here we use a model of auxotrophic Salmonella infection in germ-free mice to show that live bacterial virulence factor-driven immunogenicity can be uncoupled from inflammatory pathogenicity. Although live auxotrophic Salmonella no longer causes inflammation, its mucosal virulence factors remain the main drivers of protective mucosal immunity; virulence factor-deficient, like killed, bacteria show reduced efficacy. Assessing the involvement of innate pathogen sensing mechanisms, we show MYD88/TRIF, Caspase-1/Caspase-11 inflammasome, and NOD1/NOD2 nodosome signaling to be individually redundant. In colonized animals we show that microbiota metabolite cross-feeding may recover intestinal luminal colonization but not pathogenicity. Consequent immunoglobulin A immunity and microbial niche competition synergistically protect against Salmonella wild-type infection.

A secondary bile acid from microbiota metabolism attenuates ileitis and bile acid reduction in subclinical necrotic enteritis in chickens

BackgroundClostridium perfringens-induced chicken necrotic enteritis (NE) is responsible for substantial economic losses worldwide annually. Recently, as a result of antibiotic growth promoter prohibition, the prevalence of NE in chickens has reemerged. This study was aimed to reduce NE through titrating dietary deoxycholic acid (DCA) as an effective antimicrobial alternative.Materials and methodsDay-old broiler chicks were assigned to six groups and fed diets supplemented with 0 (basal diet), 0.8, 1.0 and 1.5 g/kg (on top of basal diet) DCA. The birds were challenged with Eimeria maxima (20,000 oocysts/bird) at d 18 and C. perfringens (109 CFU/bird per day) at d 23, 24, and 25 to induce NE. The birds were sacrificed at d 26 when ileal tissue and digesta were collected for analyzing histopathology, mRNA accumulation and C. perfringens colonization by real-time PCR, targeted metabolomics of bile acids, fluorescence in situ hybridization (FISH), or terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.ResultsAt the cellular level, birds infected with E. maxima and C. perfringens developed subclinical NE and showed shortening villi, crypt hyperplasia and immune cell infiltration in ileum. Dietary DCA alleviated the NE-induced ileal inflammation in a dose-dependent manner compared to NE control birds. Consistent with the increased histopathological scores, subclinical NE birds suffered body weight gain reduction compared to the uninfected birds, an effect attenuated with increased doses of dietary DCA. At the molecular level, the highest dose of DCA at 1.5 g/kg reduced C. perfringens luminal colonization compared to NE birds using PCR and FISH. Furthermore, the dietary DCA reduced subclinical NE-induced intestinal inflammatory gene expression and cell apoptosis using PCR and TUNEL assays. Upon further examining ileal bile acid pool through targeted metabolomics, subclinical NE reduced the total bile acid level in ileal digesta compared to uninfected birds. Notably, dietary DCA increased total bile acid and DCA levels in a dose-dependent manner compared to NE birds.ConclusionThese results indicate that DCA attenuates NE-induced intestinal inflammation and bile acid reduction and could be an effective antimicrobial alternative against the intestinal disease.

Microbial metabolite deoxycholic acid controls Clostridium perfringens-induced chicken necrotic enteritis through attenuating inflammatory cyclooxygenase signaling

Necrotic enteritis (NE) caused by Clostridium perfringens infection has reemerged as a prevalent poultry disease worldwide due to reduced usage of prophylactic antibiotics under consumer preferences and regulatory pressures. The lack of alternative antimicrobial strategies to control this disease is mainly due to limited insight into the relationship between NE pathogenesis, microbiome, and host responses. Here we showed that the microbial metabolic byproduct of secondary bile acid deoxycholic acid (DCA), at as low as 50 µM, inhibited 82.8% of C. perfringens growth in Tryptic Soy Broth (P < 0.05). Sequential Eimeria maxima and C. perfringens challenges significantly induced NE, severe intestinal inflammation, and body weight (BW) loss in broiler chickens. These negative effects were diminished (P < 0.05) by 1.5 g/kg DCA diet. At the cellular level, DCA alleviated NE-associated ileal epithelial death and significantly reduced lamina propria cell apoptosis. Interestingly, DCA reduced C. perfringens invasion into ileum (P < 0.05) without altering the bacterial ileal luminal colonization. Molecular analysis showed that DCA significantly reduced inflammatory mediators of Infγ, Litaf, Il1β, and Mmp9 mRNA accumulation in ileal tissue. Mechanism studies revealed that C. perfringens induced (P < 0.05) elevated expression of inflammatory mediators of Infγ, Litaf, and Ptgs2 (Cyclooxygenases-2 (COX-2) gene) in chicken splenocytes. Inhibiting the COX signaling by aspirin significantly attenuated INFγ-induced inflammatory response in the splenocytes. Consistent with the in vitro assay, chickens fed 0.12 g/kg aspirin diet protected the birds against NE-induced BW loss, ileal inflammation, and intestinal cell apoptosis. In conclusion, microbial metabolic product DCA prevents NE-induced BW loss and ileal inflammation through attenuating inflammatory response. These novel findings of microbiome protecting birds against NE provide new options on developing next generation antimicrobial alternatives against NE.

Persistent IL-1b Signaling Aggravates Murine Enteropathogen, Citrobacter rodentium Infection in Mice

Abstract The inflammasome cytokine IL-1b is an important mediator of the inflammatory responses against invading pathogens. However, it is not clear whether sustained IL-1b signaling following the loss of its endogenous inhibitor, secretory IL-1 receptor antagonist (sIL-1Ra), could improve mucosal immunity against the enteropathogen, Citrobacter rodentium (CR). In light of increased prescription of rec-sIL-1Ra (aka Anakinra) to treat inflammatory bowel disease, we undertook this study. At basal levels, sIL-1Ra-deficient (sIL-1RaKO) mice displayed leukocytosis and elevated inflammatory marker, i.e. serum and fecal lipocalin 2. Furthermore, bone marrow-derived macrophages and neutrophils from sIL-1RaKO mice generated higher levels of iNOS and nitrite, and ROS and NETs, respectively. These results collectively suggest sIL-1RaKO mice have low-grade chronic inflammation. Based on these results, we hypothesized that sIL-1RaKO mice with persistent IL1-b signaling could efficiently clear CR infection than their WT littermates. Oral challenge of CR (1×109 CFU/mouse) resulted in luminal colonization, which peaked at day 7 post-infection, in both groups; however, sIL-1RaKO mice displayed a higher CR burden and an exacerbated infection. The aggravated course of infection was further visualized by inoculating sIL-1RaKO mice with bioluminescent CR. Histologic analysis revealed that transmissible colonic hyperplasia was more pronounced in sIL-1RaKO mice. Interestingly, basal ileal Paneth’s cell-specific antimicrobial proteins (Ang4 and Reg3g) were significantly reduced in sIL-1RaKO mice. Collectively, our results demonstrate that a balanced mucosal IL-1b signaling is required to counter and clear enteropathogen infection.

P153 LOSS OF NEUTROPHIL EXTRACELLULAR TRAPS VIA PEPTIDYL ARGININE DEIMINASE-4 DEFICIENCY AGGRAVATES CITROBACTER RODENTIUM- INDUCED GUT INFLAMMATION

Citrobacter rodentium (CR) is an attaching-effacing enteropathogen which infects mice and causes intestinal inflammation. The CR infection model is appropriate for investigating host-pathogen interactions in the gut and understanding the pathogenesis of human inflammatory bowel diseases. Peptidyl arginine deiminase-4 (PAD4) is an enzyme required for the generation of neutrophil extracellular traps (NETs), which can provide antimicrobial effects during the host innate immune response; however, the role of PAD4 against gastrointestinal (GI) infection is largely unknown. In this study, we challenged PAD4-deficient (Pad4-/-) mice and wild type (WT) littermates against CR, and investigated bacteria clearance and gut pathology. Luminal colonization of CR in Pad4-/- mice peaked between 11-14 days post-infection (p.i.), whereas WT mice suppressed the infection by 14 days. Loss of PAD4 substantially increased CR dissemination to the spleen and mesenteric lymph nodes, which prolonged and aggravated CR-associated inflammation as indicated by splenomegaly, colomegaly and elevated systemic and colonic pro-inflammatory markers (lipocalin 2 and serum amyloid A). Likewise, the colonic antimicrobial cytokines, IL-22 and IL-17A, were more upregulated in Pad4-/- than WT mice in response to infection. Histological analysis revealed that transmissible colonic hyperplasia and goblet cell depletion were more pronounced in Pad4-/- than WT mice. Using a bioluminescent strain of CR (ICC180), we observed that the transit of CR through the gastrointestinal tract occurs more rapidly in Pad4-/- mice. Treating WT mice with deoxyribonuclease I (DNase I; disrupts NETs generation), recapitulated the exacerbated CR infection and gut pathology as in PAD4 deficient mice. Administration of the PAD4 inhibitor, Cl-amidine, also aggravated CR infection, but to a lesser extent than those observed in either Pad4-/- or DNase I-treated mice. Taken together, our findings highlight the importance of PAD4 in the mucosal clearance of CR and in resolving the gut-associated inflammation and colitis. In light of the ongoing efforts to target PAD4 or NETs to treat other inflammatory disorders, our findings caution that their inhibition may not be favorable against GI infection.

PAD4-dependent NETs generation are indispensable for intestinal clearance of Citrobacter rodentium.

Peptidyl arginine deiminase-4 (PAD4) is indispensable for generation of neutrophil extracellular traps (NETs), which can provide antimicrobial effects during host innate immune response; however, the role of PAD4 against gastrointestinal infection is largely unknown. Herein, we challenged PAD4-deficient (Pad4−/−) mice and wild-type (WT) littermates with Citrobacter rodentium (CR), and investigated bacteria clearance and gut pathology. Luminal colonization of CR in Pad4−/− mice peaked between 11–14 days post-infection, whereas WT mice suppressed the infection by 14 days. We demonstrated that Pad4−/− mice were unable to form NETs, whereas WT mice showed increased NETs formation in the colon during infection. Pad4−/− mice showed aggravated CR-associated inflammation as indicated by elevated systemic and colonic pro-inflammatory markers. Histological analysis revealed that transmissible colonic hyperplasia, goblet cell depletion, and apoptotic cell death were more pronounced in the colon of CR-infected Pad4−/− mice. Treating WT mice with deoxyribonuclease I, which can disrupt NETs generation, recapitulated the exacerbated CR infection and gut pathology associated with the loss of PAD4. Administration of the PAD4 inhibitor, Cl-amidine also aggravated CR infection, but to a lesser extent. Taken together, our findings highlight the importance of PAD4 in the mucosal clearance of CR and in resolving gut-associated inflammation.

P153 LOSS OF NEUTROPHIL EXTRACELLULAR TRAPS VIA PEPTIDYL ARGININE DEIMINASE-4 DEFICIENCY AGGRAVATES CITROBACTER RODENTIUM- INDUCED GUT INFLAMMATION

Citrobacter rodentium (CR) is an attaching-effacing enteropathogen which infects mice and causes intestinal inflammation. The CR infection model is appropriate for investigating host-pathogen interactions in the gut and understanding the pathogenesis of human inflammatory bowel diseases. Peptidyl arginine deiminase-4 (PAD4) is an enzyme required for the generation of neutrophil extracellular traps (NETs), which can provide antimicrobial effects during the host innate immune response; however, the role of PAD4 against gastrointestinal (GI) infection is largely unknown. In this study, we challenged PAD4-deficient (Pad4-/-) mice and wild type (WT) littermates against CR, and investigated bacteria clearance and gut pathology. Luminal colonization of CR in Pad4-/- mice peaked between 11-14 days post-infection (p.i.), whereas WT mice suppressed the infection by 14 days. Loss of PAD4 substantially increased CR dissemination to the spleen and mesenteric lymph nodes, which prolonged and aggravated CR-associated inflammation as indicated by splenomegaly, colomegaly and elevated systemic and colonic pro-inflammatory markers (lipocalin 2 and serum amyloid A). Likewise, the colonic antimicrobial cytokines, IL-22 and IL-17A, were more upregulated in Pad4-/- than WT mice in response to infection. Histological analysis revealed that transmissible colonic hyperplasia and goblet cell depletion were more pronounced in Pad4-/- than WT mice. Using a bioluminescent strain of CR (ICC180), we observed that the transit of CR through the gastrointestinal tract occurs more rapidly in Pad4-/- mice. Treating WT mice with deoxyribonuclease I (DNase I; disrupts NETs generation), recapitulated the exacerbated CR infection and gut pathology as in PAD4 deficient mice. Administration of the PAD4 inhibitor, Cl-amidine, also aggravated CR infection, but to a lesser extent than those observed in either Pad4-/- or DNase I-treated mice. Taken together, our findings highlight the importance of PAD4 in the mucosal clearance of CR and in resolving the gut-associated inflammation and colitis. In light of the ongoing efforts to target PAD4 or NETs to treat other inflammatory disorders, our findings caution that their inhibition may not be favorable against GI infection.

Neutrophil extracellular traps deficiency aggravates Citrobacter rodentium infection and the associated intestinal inflammation

Abstract Peptidyl arginine deiminase-4 (PAD4) is required for the formation of neutrophil extracellular traps (NETs), which is part of the host antimicrobial innate immune response. However, the role of NETs in the pathogenesis and clearance of Citrobacter rodentium (a well-characterized mouse enteropathogen) infection remains unclear. In this study, we challenged the PAD4-deficient (Pad4KO; NETs-deficient) and WT littermates with C. rodentium. Luminal colonization of C. rodentium in Pad4KO mice peaked between 11-14 days post-infection (pi), whereas WT mice cleared the infection with no detectable level of the pathogen in fecal shedding after 7-10 days. Bacterial dissemination to spleen and mesenteric lymph node was significantly higher in Pad4KO mice at day 8 and 28 pi compared to WT. Additionally; Pad4KO mice displayed splenomegaly, colomegaly and elevated colonic and systemic pro-inflammatory markers (lipocalin 2 and serum amyloid A). Histological analysis demonstrated that transmissible colonic hyperplasia and goblet cell depletion were more pronounced in Pad4KO mice. Pad4KO mice also exhibited epithelial barrier dysfunction as indicated by their heightened serum immunoreactivity to bacterial proteins. Flow cytometric analysis revealed a substantial reduction in IL-10-producing macrophages and Th17 cells in the lamina propria and spleens of Pad4KO mice compared to WT mice. However, colonic expression of IL-17A and IL-22 were highly elevated in Pad4KO mice on day 8 pi, but were attenuated on day 28 both in Pad4KO and WT mice. Taken together, our findings highlight that NETs are indispensable in promoting clearance of C. rodentium and resolving the associated intestinal inflammation.

Covering the Cover

Covering the Cover

Intestinal Epithelial Ecto-5'-Nucleotidase (CD73) Regulates Intestinal Colonization and Infection by Nontyphoidal Salmonella.

Ecto-5'-nucleotidase (CD73) is expressed abundantly on the apical surface of intestinal epithelial cells (IECs) and functions as the terminal enzyme in the generation of extracellular adenosine. Previous work demonstrated that adenosine signaling in IECs results in a number of tissue-protective effects during inflammation; however, a rationale for its apical expression has been lacking. We hypothesized that the highly polarized expression of CD73 is indicative of an important role for extracellular adenosine as a mediator of host-microbe interactions. We show that adenosine harbors bacteriostatic activity against Salmonella enterica serovar Typhimurium that is not shared by the related purine metabolite 5'-AMP, inosine, or hypoxanthine. Analysis of Salmonella colonization in IEC-specific CD73 knockout mice (CD73f/fVillinCre ) revealed a nearly 10-fold increase in colonization compared to that in controls. Despite the increased luminal colonization by Salmonella, CD73f/fVillinCre mice were protected against Salmonella colitis and showed reduced Salmonella burdens in viscera, suggesting that adenosine promotes dissemination. The knockdown of CD73 expression in cultured IECs resulted in dramatic defects in intraepithelial localization and replication as well as defective transepithelial translocation by Salmonella In conclusion, we define a novel antimicrobial activity of adenosine in the gastrointestinal tract and unveil an important role for adenosine as a regulator of host-microbe interactions. These findings have broad implications for the development of new therapeutic agents for infectious disease.

SCFA transport in rat duodenum.

Bacterial or ingested food-derived short-chain fatty acids (SCFAs) are present in the duodenal lumen. Acetate, the most abundant SCFA in the foregut lumen, is absorbed immediately after ingestion, although the mechanism by which this absorption occurs is not fully understood. We investigated the distribution and function of candidate SCFA transporters in rat duodenum. The Na(+)-coupled monocarboxylate transporter-1 (SMCT1) was localized to the brush border, whereas the pH-dependent monocarboxylate transporter (MCT) 1 and MCT4 were localized to the duodenocyte basolateral membrane. In Ussing chambered duodenal mucosa, luminal acetate dose-dependently increased short-circuit current (Isc) in the presence of serosal bumetanide and indomethacin by a luminal Na(+)-dependent, ouabain-sensitive mechanism. The Isc response was inhibited dose-dependently by the SMCT1 nonsubstrate inhibitor ibuprofen, consistent with net electrogenic absorption of acetate via SMCT1. Other SCFAs and lactate also increased Isc. Furthermore, duodenal loop perfusion of acetate increased portal venous acetate concentration, inhibited by coperfusion of ibuprofen or a MCT inhibitor. Luminal acetate perfusion increased duodenal HCO3 (-) secretion via capsaicin-sensitive afferent nerve activation and cyclooxygenase activity, consistent with absorption-mediated HCO3 (-) secretion. These results suggest that absorption of luminal SCFA via SMCT1 and MCTs increases duodenal HCO3 (-) secretion. In addition to SCFA sensing via free fatty acid receptors, the presence of rapid duodenal SCFA absorption may be important for the suppression of luminal bacterial colonization and implicated in the generation of functional dyspepsia due to bacterial overgrowth.

Gut Microbiota and Its Possible Relationship With Obesity

Obesity results from alterations in the body's regulation of energy intake, expenditure, and storage. Recent evidence, primarily from investigations in animal models, suggests that the gut microbiota affects nutrient acquisition and energy regulation. Its composition has also been shown to differ in lean vs obese animals and humans. In this article, we review the published evidence supporting the potential role of the gut microbiota in the development of obesity and explore the role that modifying the gut microbiota may play in its future treatment. Evidence suggests that the metabolic activities of the gut microbiota facilitate the extraction of calories from ingested dietary substances and help to store these calories in host adipose tissue for later use. Furthermore, the gut bacterial flora of obese mice and humans include fewer Bacteroidetes and correspondingly more Firmicutes than that of their lean counterparts, suggesting that differences in caloric extraction of ingested food substances may be due to the composition of the gut microbiota. Bacterial lipopolysaccharide derived from the intestinal microbiota may act as a triggering factor linking inflammation to high-fat diet-induced metabolic syndrome. Interactions among microorganisms in the gut appear to have an important role in host energy homeostasis, with hydrogen-oxidizing methanogens enhancing the metabolism of fermentative bacteria. Existing evidence warrants further investigation of the microbial ecology of the human gut and points to modification of the gut microbiota as one means to treat people who are over-weight or obese.

Colonization of the Cecal Mucosa by Helicobacter hepaticus Impacts the Diversity of the Indigenous Microbiota

Establishment of mucosal and/or luminal colonization is the first step in the pathogenesis of many gastrointestinal bacterial pathogens. The pathogen must be able to establish itself in the face of competition from the complex microbial community that is already in place. We used culture-independent methods to monitor the colonization of the cecal mucosa of Helicobacter-free mice following experimental infection with the pathogen Helicobacter hepaticus. Two days after infection, H. hepaticus comprised a minor component of the mucosa-associated microbiota, but within 14 days, it became the dominant member of the community. Colonization of the mucosa by H. hepaticus was associated with a decrease in the overall diversity of the microbial community, in large part due to changes in evenness resulting from the relative dominance of H. hepaticus as a member of the community. Our results demonstrate that invasion of the complex gastrointestinal microbial community by a pathogenic microorganism causes reproducible and significant disturbances in the community structure. The use of non-culture-based methods to monitor these changes should lead to a greater understanding of the ecological principles that govern pathogen invasion and may lead to novel methods for the prevention and control of gastrointestinal pathogens.

Safety and efficacy of an improved antiseptic catheter impregnated intraluminally with chlorhexidine.

The safety and efficacy of a second-generation improved antiseptic catheter impregnated with silver sulfadiazine and increased levels of chlorhexidine on its outer surface and chlorhexidine alone on its luminal surfaces was compared in vitro and in vivo to standard antiseptic catheters impregnated with these antimicrobials on their outer surfaces only. In rat and pig intravenous models, the improved antiseptic catheter was significantly more effective in resisting both outer surface and luminal colonization compared with the standard antiseptic or control catheters. There was no evidence of tissue toxicity in any group.

A prospective double blind randomized trial of urokinase flushes to prevent bacteremia due to luminal colonization of tunneled central venous catheters

The University of Texas Southwestern Medical Center at Dallas; Children's Medical Center of Dallas, Dallas, TX and Cook Children's Medical Center, Fort Worth, TX

In vitro adherence of Enterococcus faecalis and Enterococcus faecium to plastic biomaterials

In vitro adherence of Enterococcus faecalis and Enterococcus faecium to plastic biomaterials