6-Formylindolo (3, 2-b) Carbazole (FICZ)–mediated protection of gut barrier is dependent on T cells in a mouse model of alcohol combined with burn injury

6-Formylindolo (3, 2-b) Carbazole (FICZ) is a ligand of aryl hydrocarbon receptor (AHR) which regulates Th17 release of IL-17 and IL-22 production. Earlier, we showed that ethanol combined with burn injury suppresses Th17 responses and disrupts intestinal barrier leading to increased gut bacterial growth and translocation. Since IL-22 is known for its role in intestinal barrier maintenance, we determined whether treatment of mice with FICZ restores T cell IL-22 release and protects intestine barrier following ethanol and burn injury. Wildtype and Rag1−/− mice were gavaged with ~2.9 g/kg ethanol or water, and given a ~12.5% total body surface area burn. Mice were given FICZ (5 μg) in resuscitation fluid. FICZ treatment of wildtype mice normalized IL-22 and IL-17 in lamina propria and spleen T cells, as well as increased CYP1A1 expression in spleen T cells. This was accompanied by improved gut motility, decreased copy number of small intestine total bacteria and Enterobacteriaceae, attenuation of intestinal tissue levels of IL-6, KC, IL-18, decreased apoptosis, and prevention of gut leakiness following ethanol and burn injury. However, FICZ treatment of Rag1−/− mice did not improve any of the parameters listed after ethanol and burn injury. Additional data generated using mice treated with recombinant IL-22 alone or in combination with anti-IL-18 antibody suggest that full protection of gut barrier integrity requires both IL-18 inhibition and IL-22 restoration following ethanol and burn injury. Together our findings suggest that AHR ligand FICZ may have better therapeutic potential for maintenance of gut barrier function after ethanol and burn injury.     

Gram-negative bacteria aggravate murine small intestinal Th1-type immunopathology following oral infection with Toxoplasma gondii

Oral infection of susceptible mice with Toxoplasma gondii results in Th1-type immunopathology in the ileum. We investigated gut flora changes during ileitis and determined contributions of gut bacteria to intestinal inflammation. Analysis of the intestinal microflora revealed that ileitis was accompanied by increasing bacterial load, decreasing species diversity, and bacterial translocation. Gram-negative bacteria identified as Escherichia coli and Bacteroides/Prevotella spp. accumulated in inflamed ileum at high concentrations. Prophylactic or therapeutic administration of ciprofloxacin and/or metronidazole ameliorated ileal immunopathology and reduced intestinal NO and IFN-gamma levels. Most strikingly, gnotobiotic mice in which cultivable gut bacteria were removed by quintuple antibiotic treatment did not develop ileitis after Toxoplasma gondii infection. A reduction in total numbers of lymphocytes was observed in the lamina propria of specific pathogen-free (SPF), but not gnotobiotic, mice upon development of ileitis. Relative numbers of CD4(+) T cells did not differ in naive vs infected gnotobiotic or SPF mice, but infected SPF mice showed a significant increase in the frequencies of activated CD4(+) T cells compared with gnotobiotic mice. Furthermore, recolonization with total gut flora, E. coli, or Bacteroides/Prevotella spp., but not Lactobacillus johnsonii, induced immunopathology in gnotobiotic mice. Animals recolonized with E. coli and/or total gut flora, but not L. johnsonii, showed elevated ileal NO and/or IFN-gamma levels. In conclusion, Gram-negative bacteria, i.e., E. coli, aggravate pathogen-induced intestinal Th1-type immunopathology. Thus, pathogen-induced acute ileitis may prove useful to study bacteria-host interactions in small intestinal inflammation and to test novel therapies based on modulation of gut flora.     

Inadequate Clearance of Translocated Bacterial Products in HIV-Infected Humanized Mice

Bacterial translocation from the gut and subsequent immune activation are hallmarks of HIV infection and are thought to determine disease progression. Intestinal barrier integrity is impaired early in acute retroviral infection, but levels of plasma lipopolysaccharide (LPS), a marker of bacterial translocation, increase only later. We examined humanized mice infected with HIV to determine if disruption of the intestinal barrier alone is responsible for elevated levels of LPS and if bacterial translocation increases immune activation. Treating uninfected mice with dextran sodium sulfate (DSS) induced bacterial translocation, but did not result in elevated plasma LPS levels. DSS-induced translocation provoked LPS elevation only when phagocytic cells were depleted with clodronate liposomes (clodrolip). Macrophages of DSS-treated, HIV-negative mice phagocytosed more LPS ex vivo than those of control mice. In HIV-infected mice, however, LPS phagocytosis was insufficient to clear the translocated LPS. These conditions allowed higher levels of plasma LPS and CD8+ cell activation, which were associated with lower CD4+/CD8+ cell ratios and higher viral loads. LPS levels reflect both intestinal barrier and LPS clearance. Macrophages are essential in controlling systemic bacterial translocation, and this function might be hindered in chronic HIV infection.     

The cotton stainer's gut microbiota suppresses infection of a cotransmitted trypanosomatid parasite

The evolutionary and ecological success of many insects is attributed to mutualistic partnerships with bacteria that confer hosts with novel traits including food digestion, nutrient supplementation, detoxification of harmful compounds and defence against natural enemies. Dysdercus fasciatus firebugs (Hemiptera: Pyrrhocoridae), commonly known as cotton stainers, possess a simple but distinctive gut bacterial community including B vitamin‐supplementing Coriobacteriaceae symbionts. In addition, their guts are often infested with the intestinal trypanosomatid parasite Leptomonas pyrrhocoris (Kinetoplastida: Trypanosomatidae). In this study, using experimental bioassays and fluorescence in situ hybridization (FISH), we report on the protective role of the D. fasciatus gut bacteria against L. pyrrhocoris. We artificially infected 2nd instars of dysbiotic and symbiotic insects with a parasite culture and measured parasite titres, developmental time and survival rates. Our results show that L. pyrrhocoris infection increases developmental time and slightly modifies the quantitative composition of the gut microbiota. More importantly, we found significantly higher parasite titres and a tendency towards lower survival rates in parasite‐infected dysbiotic insects compared to symbiotic controls, indicating that the gut bacteria successfully interfere with the establishment or proliferation of L. pyrrhocoris. The colonization of symbiotic bacteria on the peritrophic matrix along the gut wall, as revealed by FISH, likely acts as a barrier blocking parasite attachment or entry into the hemolymph. Our findings show that in addition to being nutritionally important, D. fasciatus’ gut bacteria complement the host's immune system in preventing parasite invasions and that a stable gut microbial community is integral for the host's health.     

Endogenous infection in mice with streptozotocin-induced diabetes. A feature of bacterial translocation

Slc:ddY mice that received a single intraperitoneal injection of 200 mg/kg streptozotocin (STZ) were examined for persistency of diabetes (changes of indigenous bacterial floras, and bacterial translocation. Significant diabetes (increase in plasma glucose and decrease in insulin) was recognized 2 weeks after the injection, and persisted for 12 weeks. The numbers of aerobic gram-negative bacilli, staphylococci (including micrococci), and streptococci in caecal and oral floras were significantly increased, but the numbers of anaerobic bacteria in caecal flora were hardly changed. Bacterial translocation of indigenous bacteria to the mesenteric lymph node, lung, or kidney was detectable in some mice 2 weeks after the injection. The incidence of bacterial translocation in these STZ-treated mice then increased; infection caused by several organisms, e.g., Klebsiella pneumoniae, Staphylococcus epidermidis, streptococci, or Lactobacillus sp., occurred in lung, liver, spleen, kidneys, and mesenteric lymph node. No indigenous bacteria were cultured from these organs of control mice. This endogenous infection may have been due to the over population of several bacterial strains caused by disruption of indigenous floras along with depression of immunological function.     

Gut-associated lymphoid T cell suppression enhances bacterial translocation in alcohol and burn injury

The mechanism of alcohol-mediated increased infection in burn patients remains unknown. With the use of a rat model of acute alcohol and burn injury, the present study ascertained whether acute alcohol exposure before thermal injury enhances gut bacterial translocation. On day 2 postinjury, we found a severalfold increase in gut bacterial translocation in rats receiving both alcohol and burn injury compared with the animals receiving either injury alone. Whereas there were no demonstrable changes in intestinal morphology in any group of animals, a significant increase in intestinal permeability was observed in ethanol- and burn-injured rats compared with the rats receiving either injury alone. We further examined the role of intestinal immune defense by determining the gut-associated lymphoid (Peyer's patches and mesenteric lymph nodes) T cell effector responses 2 days after alcohol and burn injury. Although there was a decrease in the proliferation and interferon-gamma by gut lymphoid T cells after burn injury alone; the suppression was maximum in the group of rats receiving both alcohol and burn injuries. Furthermore, the depletion of CD3(+) cells in healthy rats resulted in bacterial accumulation in mesenteric lymph nodes; such CD3(+) cell depletion in alcohol- and burn-injured rats furthered the spread of bacteria to spleen and circulation. In conclusion, our data suggest that the increased intestinal permeability and a suppression of intestinal immune defense in rats receiving alcohol and burn injury may cause an increase in bacterial translocation and their spread to extraintestinal sites.     

Hypoxia-inducible Factor-dependent Regulation of Platelet-activating Factor Receptor as a Route for Gram-Positive Bacterial Translocation across Epithelia

Mucosal surfaces, such as the lung and intestine, are lined by a monolayer of epithelia that provides tissue barrier and transport function. It is recently appreciated that a common feature of inflammatory processes within the mucosa is hypoxia (so-called inflammatory hypoxia). Given the strong association between bacterial translocation and mucosal inflammatory disease, we hypothesized that intestinal epithelial hypoxia influences bacterial translocation. Initial studies revealed that exposure of cultured intestinal epithelia to hypoxia (pO₂, 20 torr; 24–48 h) resulted in a increase of up to 40-fold in the translocation of some strains of Gram-positive bacteria, independently of epithelial barrier function. A screen of relevant pathway inhibitors identified a prominent role for the platelet-activating factor receptor (PAFr) in hypoxia-associated bacterial translocation, wherein pharmacologic antagonists of PAFr blocked bacterial translocation by as much as 80 ± 6%. Extensions of these studies revealed that hypoxia prominently induces PAFr through a hypoxia-inducible factor (HIF)-dependent mechanism. Indeed, HIF and PAFr loss of function studies (short hairpin RNA) revealed that apically expressed PAFr is central to the induction of translocation for the Gram-positive bacteria Enterococcus faecalis. Together, these findings reveal that some strains of Gram-positive bacteria exploit HIF-regulated PAFr as a means for translocation through intestinal epithelial cells.     

Use of superoxide dismutase and catalase producing lactic acid bacteria in TNBS induced Crohn's disease in mice

Reactive oxygen species are involved in various aspects of intestinal inflammation and tumor development. Decreasing their levels using antioxidant enzymes, such as catalase (CAT) or superoxide dismutase (SOD) could therefore be useful in the prevention of certain diseases. Lactic acid bacteria (LAB) are ideal candidates to deliver these enzymes in the gut. In this study, the anti-inflammatory effects of CAT or SOD producing LAB were evaluated using a trinitrobenzenesulfonic acid (TNBS) induced Crohn's disease murine model. Engineered Lactobacillus casei BL23 strains producing either CAT or SOD, or the native strain were given to mice before and after intrarectal administration of TNBS. Animal survival, live weight, intestinal morphology and histology, enzymatic activities, microbial translocation to the liver and cytokines released in the intestinal fluid were evaluated. The mice that received CAT or SOD-producing LAB showed a faster recovery of initial weight loss, increased enzymatic activities in the gut and lesser extent of intestinal inflammation compared to animals that received the wild-type strain or those that did not receive bacterial supplementation. Our findings suggest that genetically engineered LAB that produce antioxidant enzymes could be used to prevent or decrease the severity of certain intestinal pathologies.     

Diabetes progression and alterations in gut bacterial translocation: prevention by diet supplementation with human milk in NOD mice

Impaired intestinal barrier function occurs before type 1 diabetes (T1D) onset with a possible contribution of microbial translocation. Breastfeeding is associated with enhanced mucosal intestinal integrity and T1D protection. Our aim was to study the potential of human milk (HM) to prevent diabetes onset and modulate the translocation of gut bacteria susceptible to breastfeeding or associated to diabetes onset. We show that HM intake can prevent T1D in nonobese diabetic mice independently of bifidobacteria colonization. Prior to diabetes onset, HM mice harbored splenic bacterial counts and plasma lipopolysaccharides level similar to control mice but exhibited a reduced expansion of Anaerotruncus sp. in pancreas and Lactobacillus johnsonii and Barnesiella in Peyer's patches (PP). Surprisingly, pancreas and PP bacterial expansion did not correlate with their own gut localization but with ileal Escherichia coli and cecal HM-susceptible bacteria (the promoted L. murinus and Bacteroides vulgatus, and the repressed B. fragilis and E. coli), respectively. Besides, higher colonic B. vulgatus counts induced by HM intake were associated with low islet infiltration and pancreatic E. coli expansion. On another hand, splenic dendritic cells (DCs) were identified as negative covariate of PP Barnesiella, suggesting a possible HM contribution to preserving splenic DCs through the reduction of Barnesiella translocation. Fecal B. vulgatus also negatively correlated with PP Barnesiella expansion, indicating that the mouse coprophagic behavior likely added to HM effect. Our findings provide evidence that HM has a multilevel impact and cooperates with some gut bacteria for controlling bacterial translocation at the earliest stage of insulitis.     

Intestinal inflammation alters mucosal carbohydrate foraging and monosaccharide incorporation into microbial glycans

Endogenous carbohydrates released from the intestinal mucus represent a constant source of nutrients to the intestinal microbiota. Mucus‐derived carbohydrates can also be used as building blocks in the biosynthesis of bacterial cell wall components, thereby influencing host mucosal immunity. To assess the uptake of endogenous carbohydrates by gut microbes in healthy mice and during intestinal inflammation, we applied azido‐monosaccharides that can be tracked on bacterial cell walls after conjugation with fluorophores. In interleukin‐10 deficient mice, changes in the gut microbiota were accompanied by decreased carbohydrate hydrolase activities and increased lumenal concentrations of host glycan‐derived monosaccharides. Tracking of the monosaccharide N‐azidoacetylglucosamine (GlcNAz) in caecum bacteria revealed a preferential incorporation of this carbohydrate by Xanthomonadaceae in healthy mice and by Bacteroidaceae in interleukin‐10 deficient mice. These GlcNAz‐positive Bacteroidaceae fractions mainly belonged to the species B. acidifaciens and B. vulgatus. Growth of Bacteroides species in the presence of specific monosaccharides changed their stimulatory activity toward CD11c⁺ dendritic cells. Expression of activation markers and cytokine production was highest after stimulation of dendritic cells with B. vulgatus. The variable incorporation of monosaccharides by related Bacteroides species underline the necessity to investigate intestinal bacteria down to the species level when addressing microbiota‐host interactions.     

抗生素所致腹泻大鼠肠屏障功能损伤及乳酸杆菌保护机制的研究

目的探讨抗生素对所致腹泻大鼠肠道屏障功能、肠道菌群结构和肠道细菌移位的影响及乳酸杆菌制剂的保护机制。方法采用细菌培养法动态测定抗生素所致腹泻大鼠肠道菌群变化及肠系膜淋巴结、肝脏、脾脏和结肠组织的移位细菌量;应用光镜和电子显微镜观察肠黏膜组织超微结构变化。结果应用抗生素可致大鼠腹泻,肠道菌群失调,肠黏膜组织受损,发生肠道细菌移位。大肠埃希菌攻击可加重肠道菌群失调和肠黏膜损伤程度,促发细菌移位发生。乳酸杆菌可扶正肠菌群结构,修复损伤的肠黏膜,抑制肠细菌移位发生。结论阐明了抗生素、肠黏膜屏障功能、肠道菌群结构和肠道细菌移位间的互为因果,相互影响的关系。微生态制剂在维持机体微生态平衡、修复肠黏膜方面具有保护作用。     

Ultrastructural study on route of gut bacterial translocation in a rat after spinal cord injury

Objective: To observe the ultrastructural change of the route of gut bacterial translocation in a rat with spinal cord injury(SCI).Methods: Forty Wistar rats were divided into the following groups: control group and 3 SCI groups(10 in each group). The rats in the SCI groups were established SCI model at 24 h, 48 h, and 72 h after SCI. Small intestine mucous membrane tissue was identified and assayed by transmission electron microscope, scanning electron microscope and immunofluorescence microscopy. Results: Small intestine mucous membrane tissue in control group was not damaged significantly, but those in SCI groups were damaged significantly. Proliferation bacteria in gut lumen attached on microvilli. The extracellular bacteria torn the intestinal barrier and perforated into the small intestinal mucosal epithelial cell. The bacteria and a lot of particles of the seriously damaged region penetrated into the lymphatic system and the blood system directly. Some bacteria were internalized into the goblet cell through the apical granule. Some bacteria and particles perforated into the submucosa of the M cell running the long axis of M cells through the tight junctions. In the microcirculation of mucosa, the bacteria that had already broken through the microvilli into blood circulation swim accompanying with erythrocytes. Conclusion: The routes of bacterial translocation interact and format a vicious circle. At early step, the transcellular pathway of bacterial translocation is major. Following with the destroyed small intestine mucous, the routes of bacterial translocation through the lymphatic system and the blood system become direct pathways. The goblet cell-dendritic cell and M cell pathway also play an important role in the bacterial translocation.     

TLR9 limits enteric antimicrobial responses and promotes microbiota‐based colonisation resistance during Citrobacter rodentium infection

Mammalian cells express an array of toll‐like receptors to detect and respond to microbial pathogens, including enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC). These clinically important attaching and effacing (A/E) pathogens infect the apical surface of intestinal epithelial cells, causing inflammation as well as severe diarrheal disease. Because EPEC and EHEC are human‐specific, the related murine pathogen Citrobacter rodentium has been widely used to define how hosts defend against A/E pathogens. This study explored the role of TLR9, a receptor that recognises unmethylated CpG dinucleotides present in bacterial DNA, in promoting host defence against C. rodentium. Infected Tlr9^?/? mice suffered exaggerated intestinal damage and carried significantly higher (10–100 fold) pathogen burdens in their intestinal tissues as compared with wild type (WT) mice. C. rodentium infection also induced increased antimicrobial responses, as well as hyperactivation of NF‐κB signalling in the intestines of Tlr9^?/? mice. These changes were associated with accelerated depletion of the intestinal microbiota in Tlr9^?/? mice as compared with WT mice. Notably, antibiotic‐based depletion of the gut microbiota in WT mice prior to infection increased their susceptibility to the levels seen in Tlr9^?/? mice. Our results therefore indicate that TLR9 signalling suppresses intestinal antimicrobial responses, thereby promoting microbiota‐mediated colonisation resistance against C. rodentium infection.     

Aging aggravates ischemic stroke‐induced brain damage in mice with chronic peripheral infection

Ischemic stroke is confounded by conditions such as atherosclerosis, diabetes, and infection, all of which alter peripheral inflammatory processes with concomitant impact on stroke outcome. The majority of the stroke patients are elderly, but the impact of interactions between aging and inflammation on stroke remains unknown. We thus investigated the influence of age on the outcome of stroke in animals predisposed to systemic chronic infection. Th1‐polarized chronic systemic infection was induced in 18–22 month and 4‐month‐old C57BL/6j mice by administration of Trichuris muris (gut parasite). One month after infection, mice underwent permanent middle cerebral artery occlusion and infarct size, brain gliosis, and brain and plasma cytokine profiles were analyzed. Chronic infection increased the infarct size in aged but not in young mice at 24 h. Aged, ischemic mice showed altered plasma and brain cytokine responses, while the lesion size correlated with plasma prestroke levels of RANTES. Moreover, the old, infected mice exhibited significantly increased neutrophil recruitment and upregulation of both plasma interleukin‐17α and tumor necrosis factor‐α levels. Neither age nor infection status alone or in combination altered the ischemia‐induced brain microgliosis. Our results show that chronic peripheral infection in aged animals renders the brain more vulnerable to ischemic insults, possibly by increasing the invasion of neutrophils and altering the inflammation status in the blood and brain. Understanding the interactions between age and infections is crucial for developing a better therapeutic regimen for ischemic stroke and when modeling it as a disease of the elderly.     

Like Will to Like: Abundances of Closely Related Species Can Predict Susceptibility to Intestinal Colonization by Pathogenic and Commensal Bacteria

The intestinal ecosystem is formed by a complex, yet highly characteristic microbial community. The parameters defining whether this community permits invasion of a new bacterial species are unclear. In particular, inhibition of enteropathogen infection by the gut microbiota ( = colonization resistance) is poorly understood. To analyze the mechanisms of microbiota-mediated protection from Salmonella enterica induced enterocolitis, we used a mouse infection model and large scale high-throughput pyrosequencing. In contrast to conventional mice (CON), mice with a gut microbiota of low complexity (LCM) were highly susceptible to S. enterica induced colonization and enterocolitis. Colonization resistance was partially restored in LCM-animals by co-housing with conventional mice for 21 days (LCM^con21). 16S rRNA sequence analysis comparing LCM, LCM^con21 and CON gut microbiota revealed that gut microbiota complexity increased upon conventionalization and correlated with increased resistance to S. enterica infection. Comparative microbiota analysis of mice with varying degrees of colonization resistance allowed us to identify intestinal ecosystem characteristics associated with susceptibility to S. enterica infection. Moreover, this system enabled us to gain further insights into the general principles of gut ecosystem invasion by non-pathogenic, commensal bacteria. Mice harboring high commensal E. coli densities were more susceptible to S. enterica induced gut inflammation. Similarly, mice with high titers of Lactobacilli were more efficiently colonized by a commensal Lactobacillus reuteri ^RR strain after oral inoculation. Upon examination of 16S rRNA sequence data from 9 CON mice we found that closely related phylotypes generally display significantly correlated abundances (co-occurrence), more so than distantly related phylotypes. Thus, in essence, the presence of closely related species can increase the chance of invasion of newly incoming species into the gut ecosystem. We provide evidence that this principle might be of general validity for invasion of bacteria in preformed gut ecosystems. This might be of relevance for human enteropathogen infections as well as therapeutic use of probiotic commensal bacteria.     

骶神经电刺激对脊髓损伤大鼠肠黏膜机械屏障的保护作用

目的：观察骶神经电刺激对脊髓损伤大鼠肠黏膜机械屏障的保护作用。方法：56只Wistar大鼠分7组（n=8）：正常组、急性完全性脊髓损伤（SCI）组和骶神经电刺激组（按24、48、72h各8只）。进行内毒素测定;肠系膜淋巴结、肝脏、脾脏菌培养;肠道形态学观察;紧密连接蛋白zo-1的蛋白表达测定。结果：对照组肠黏膜不同程度损伤;肠道上皮细胞及细胞间连接破坏;内毒素血症和细菌移位明显。实验组肠黏膜得到改善,内毒素水平下降且细菌移位减少。ZO-1蛋白表达无统计学差异。对照组ZO-1的分布出现不同程度的散乱、排列不规则,实验组分布得到改善。结论：骶神经电刺激可促肠蠕动、排肠内容物、减少肠道菌群数量,保护肠黏膜上皮细胞及紧密连接的机械屏障,减少细菌移位和内毒素血症。     

Gut physiology mediates a trade‐off between adaptation to malnutrition and susceptibility to food‐borne pathogens

The animal gut plays a central role in tackling two common ecological challenges, nutrient shortage and food‐borne parasites, the former by efficient digestion and nutrient absorption, the latter by acting as an immune organ and a barrier. It remains unknown whether these functions can be independently optimised by evolution, or whether they interfere with each other. We report that Drosophila melanogaster populations adapted during 160 generations of experimental evolution to chronic larval malnutrition became more susceptible to intestinal infection with the opportunistic bacterial pathogen Pseudomonas entomophila. However, they do not show suppressed immune response or higher bacterial loads. Rather, their increased susceptibility to P. entomophila is largely mediated by an elevated predisposition to loss of intestinal barrier integrity upon infection. These results may reflect a trade‐off between the efficiency of nutrient extraction from poor food and the protective function of the gut, in particular its tolerance to pathogen‐induced damage.     

Alternatively activated macrophages in intestinal helminth infection: effects on concurrent bacterial colitis

The distribution of several pathogenic helminth infections coincides geographically with many devastating microbial diseases, including enteric bacterial infections. To dissect the mechanisms by which helminths modulate the host's response to enteric bacteria and bacteria-mediated intestinal inflammation, we have recently established a coinfection model and shown that coinfection with the helminth Heligmosomoides polygyrus exacerbates colitis induced by infection with the gram-negative bacterial pathogen Citrobacter rodentium. The disease severity of the coinfected mice was correlated with high Citrobacter loads in the gut, translocation of the bacteria into mucosal and systemic immune compartments, delayed bacterial clearance, and a significantly enhanced colonic TNF-alpha response. In the present study, using our in vivo coinfection model as well as in vitro approaches, we test the hypothesis that the phenotypic and functional alterations in macrophages induced by the helminth-driven T cell response may contribute to the observed alterations in the response to C. rodentium. We show that via a STAT6-dependent mechanism H. polygyrus coinfection results in a marked infiltration into the colonic lamina propria of F4/80+ cells that have the phenotype of alternatively activated macrophages. Functional analysis of these macrophages further shows that they are impaired in their killing of internalized bacteria. Yet, these cells produce an enhanced amount of TNF-alpha in response to C. rodentium infection. These results demonstrate that helminth infection can impair host protection against concurrent enteric bacterial infection and promote bacteria-induced intestinal injury through a mechanism that involves the induction of alternatively activated macrophages.     

Engineering bacterial thiosulfate and tetrathionate sensors for detecting gut inflammation

There is a groundswell of interest in using genetically engineered sensor bacteria to study gut microbiota pathways, and diagnose or treat associated diseases. Here, we computationally identify the first biological thiosulfate sensor and an improved tetrathionate sensor, both two‐component systems from marine Shewanella species, and validate them in laboratory Escherichia coli. Then, we port these sensors into a gut‐adapted probiotic E. coli strain, and develop a method based upon oral gavage and flow cytometry of colon and fecal samples to demonstrate that colon inflammation (colitis) activates the thiosulfate sensor in mice harboring native gut microbiota. Our thiosulfate sensor may have applications in bacterial diagnostics or therapeutics. Finally, our approach can be replicated for a wide range of bacterial sensors and should thus enable a new class of minimally invasive studies of gut microbiota pathways.