Can microbiota transplantation abrogate murine colonization resistance against Campylobacter jejuni?

Investigating causality with fecal microbiota transplantation in rodents: applications, recommendations and pitfalls

In recent years, studies investigating the role of the gut microbiota in health and diseases have increased enormously - making it essential to deepen and question the research methodology employed. Fecal microbiota transplantation (FMT) in rodent studies (either from human or animal donors) allows us to better understand the causal role of the intestinal microbiota across multiple fields. However, this technique lacks standardization and requires careful experimental design in order to obtain optimal results. By comparing several studies in which rodents are the final recipients of FMT, we summarize the common practices employed. In this review, we document the limitations of this method and highlight different parameters to be considered while designing FMT Studies. Standardizing this method is challenging, as it differs according to the research topic, but avoiding common pitfalls is feasible. Several methodological questions remain unanswered to this day and we offer a discussion on issues to be explored in future studies.

Psychobiotic Effects of Multi-Strain Probiotics Originated from Thai Fermented Foods in a Rat Model

This work aimed to investigate the psychobiotic effects of six bacterial strains on the mind and behavior of male Wistar rats. The probiotic (PRO) group (n=7) were rats pre-treated with antibiotics for 7 days followed by 14-day probiotic administration, antibiotics (ANT) group (n=7) were rats treated with antibiotics for 21 days without probiotics. The control (CON) group (n=7) were rats that received sham treatment for 21 days. The six bacterial strains with probiotic properties were mostly isolated from Thai fermented foods; Pedicoccus pentosaceus WS11, Lactobacillus plantarum SK321, L. fermentum SK324, L. brevis TRBC 3003, Bifidobacterium adolescentis TBRC 7154 and Lactococcus lactis subsp. lactis TBRC 375. The probiotics were freeze-dried into powder (6×109 CFU/5 g) and administered to the PRO group via oral gavage. Behavioral tests were performed. The PRO group displayed significantly reduced anxiety level and increased locomotor function using a marble burying test and open field test, respectively and significantly improved short-term memory performance using a novel object recognition test. Antibiotics significantly reduced microbial counts in rat feces in the ANT group by 100 fold compared to the PRO group. Probiotics significantly enhanced antioxidant enzymatic and non-enzymatic defenses in rat brains as assessed using catalase activity and ferric reducing antioxidant power assay, respectively. Probiotics also showed neuroprotective effects with less pyknotic cells and lower frequency of vacuolization in cerebral cortex. This multi-strain probiotic formulation from Thai fermented foods may offer a potential to develop psychobiotic-rich functional foods to modulate human mind and behaviors.

Murine fecal microbiota transplantation lowers gastrointestinal pathogen loads and dampens pro-inflammatory immune responses in Campylobacter jejuni infected secondary abiotic mice

Conventional mice are protected from Campylobacter jejuni infection by the murine host-specific gut microbiota composition. We here addressed whether peroral fecal microbiota transplantation (FMT) might be an antibiotics-independent option to lower even high gastrointestinal C. jejuni loads in the infected vertebrate host. To address this, secondary abiotic mice were generated by broad-spectrum antibiotic treatment and perorally infected with C. jejuni by gavage. One week later, mice were stably colonized with more than 109 C. jejuni and subjected to peroral FMT from murine donors on three consecutive days. Two weeks post-intervention, gastrointestinal C. jejuni loads were up to 7.5 orders of magnitude lower following murine FMT versus mock challenge. Remarkably, FMT reversed C. jejuni induced colonic epithelial apoptosis, but enhanced proliferative and regenerative responses in the colon thereby counteracting pathogenic cell damage. Furthermore, FMT dampened both, innate and adaptive immune cell responses in the large intestines upon C. jejuni infection that were accompanied by less C. jejuni-induced colonic nitric oxide secretion. Our study provides strong evidence that novel probiotic formulations developed as alternative option to FMT in severe intestinal inflammatory morbidities including Clostridoides difficile infection might be effective to treat campylobacteriosis and lower pathogen loads in colonized vertebrates including farm animals.

Murine Fecal Microbiota Transplantation Alleviates Intestinal and Systemic Immune Responses in Campylobacter jejuni Infected Mice Harboring a Human Gut Microbiota

Human campylobacteriosis constitutes a zoonotic food-borne disease and a progressively rising health burden of significant socioeconomic impact. We have recently shown that conventional mice are protected from Campylobacter jejuni infection, which was not the case for human microbiota associated (hma) mice indicating that the host-specific gut microbiota composition primarily determines susceptibility to or resistance against C. jejuni infection. In our present preclinical intervention study we addressed whether gut microbiota changes in stably C. jejuni infected hma mice following murine fecal microbiota transplantation (mFMT) could alleviate pathogen-induced immune responses. To accomplish this, secondary abiotic C57BL/6 mice were generated by broad-spectrum antibiotic treatment, perorally reassociated with a complex human gut microbiota and challenged with C. jejuni by gavage. Seven days later C. jejuni infected hma mice were subjected to peroral mFMT on 3 consecutive days. Within a week post-mFMT fecal pathogenic burdens had decreased by two orders of magnitude, whereas distinct changes in the gut microbiota composition with elevated numbers of lactobacilli and bifidobacteria could be assessed. In addition, mFMT resulted in less C. jejuni induced apoptotic responses in colonic epithelia, reduced numbers of macrophages and monocytes as well as of T lymphocytes in the large intestinal mucosa and lamina propria and in less distinct intestinal pro-inflammatory cytokine secretion as compared to mock challenge. Strikingly, inflammation dampening effects of mFMT were not restricted to the intestinal tract, but could also be observed systemically as indicated by elevated serum concentrations of pro-inflammatory cytokines such as TNF-α, IL-12p70, and IL-6 in C. jejuni infected hma mice of the mock, but not the mFMT cohort. In conclusion, our preclinical mFMT intervention study provides evidence that changes in the gut microbiota composition which might be achieved by pre- or probiotic formulations may effectively lower intestinal C. jejuni loads, dampen both, pathogen-induced intestinal and systemic inflammatory sequelae and may represent a useful tool to treat continuous shedding of C. jejuni by asymptomatic carriers which is critical in the context of food production, hospitalization and immunosuppression.

The Effect of Co-infection of Food-Borne Pathogenic Bacteria on the Progression of Campylobacter jejuni Infection in Mice

Campylobacter is a well-known food-borne pathogen that causes human gastroenteritis. Food products that contain Campylobacter may also be contaminated by other pathogens, however, whether this multiple contamination leads to more severe infection remains unclear. In this study, mice were gavaged with Campylobacter jejuni and other food-borne pathogenic bacteria to mimic a multiple infection. It was demonstrated that the C. jejuni load was elevated when the mice were co-infected with C. jejuni and Salmonella typhimurium, and the campylobacteriosis that followed was also enhanced, with features of decreased body weight, heavier bloody stools and more pronounced inflammatory changes to the colon. In addition, infection with C. jejuni was also promoted by co-infection with entero-invasive Escherichia coli but unaffected over time. In contrast to S. typhimurium and entero-invasive E. coli, co-infection by Listeria monocytogenes showed little effect on C. jejuni infection and even hindered its progress. In addition, the intestinal microecology was also affected by co-infection of C. jejuni with other pathogens, with an increased relative abundance of unclassified Enterobacteriaceae, decreased levels of butyric acid and changes in the abundance of several genera of gut microbe, which suggests that some food-borne pathogenic bacteria might affect the progression of C. jejuni infection in mice by influencing the composition of the gut microbiota and the resulting changes in SCFA levels. Collectively, our findings suggest that co-infection of Campylobacter with other pathogenic bacteria can impact on the progression of infection by C. jejuni in mice, which may also have implication for the etiology of Campylobacter on human health.

Intestinal, extra-intestinal and systemic sequelae of Toxoplasma gondii induced acute ileitis in mice harboring a human gut microbiota

Background

Within seven days following peroral high dose infection with Toxoplasma gondii susceptible conventionally colonized mice develop acute ileitis due to an underlying T helper cell (Th) -1 type immunopathology. We here addressed whether mice harboring a human intestinal microbiota developed intestinal, extra-intestinal and systemic sequelae upon ileitis induction.

Methodology/Principal findings

Secondary abiotic mice were generated by broad-spectrum antibiotic treatment and associated with a complex human intestinal microbiota following peroral fecal microbiota transplantation. Within three weeks the human microbiota had stably established in the murine intestinal tract as assessed by quantitative cultural and culture-independent (i.e. molecular 16S rRNA based) methods. At day 7 post infection (p.i.) with 50 cysts of T. gondii strain ME49 by gavage human microbiota associated (hma) mice displayed severe clinical, macroscopic and microscopic sequelae indicating acute ileitis. In diseased hma mice increased numbers of innate and adaptive immune cells within the ileal mucosa and lamina propria and elevated intestinal secretion of pro-inflammatory mediators including IFN-γ, IL-12 and nitric oxide could be observed at day 7 p.i. Ileitis development was accompanied by substantial shifts in intestinal microbiota composition of hma mice characterized by elevated total bacterial loads and increased numbers of intestinal Gram-negative commensals such as enterobacteria and Bacteroides / Prevotella species overgrowing the small and large intestinal lumen. Furthermore, viable bacteria translocated from the inflamed ileum to extra-intestinal including systemic compartments. Notably, pro-inflammatory immune responses were not restricted to the intestinal tract as indicated by increased pro-inflammatory cytokine secretion in extra-intestinal (i.e. liver and kidney) and systemic compartments including spleen and serum.

Conclusion/Significance

With respect to the intestinal microbiota composition “humanized” mice display acute ileitis following peroral high dose T. gondii infection. Thus, hma mice constitute a suitable model to further dissect the interactions between pathogens, human microbiota and vertebrate host immunity during acute intestinal inflammation.

Campylobacter jejuni infection of conventionally colonized mice lacking nucleotide-oligomerization-domain-2

Background

The nucleotide-binding oligomerisaton protein 2 (NOD2) constitutes a pivotal sensor of bacterial muramyl dipeptide and assures expression of distinct antimicrobial peptides and mediators produced by enterocytes and immune cells directed against pathogens including Campylobacter jejuni. We here elucidated the role of NOD2 during murine C. jejuni infection in more detail.

Results

Conventionally colonized NOD2 deficient (NOD2^−/−) mice and corresponding wildtype (WT) counterparts were perorally infected with C. jejuni strain 81–176 on three consecutive days. The pathogen colonized both WT and NOD2^−/− mice only sporadically until day 14 post infection (p.i.). However, the slightly higher prevalence of C. jejuni in NOD2^−/− mice was accompanied by higher intestinal Escherichia coli loads known to facilitate C. jejuni colonization. Neither overt macroscopic (clinical) nor microscopic sequelae (such as colonic epithelial apoptosis) could be observed upon murine C. jejuni infection of either genotype. Innate immune responses were less distinctly induced in C. jejuni infected NOD2^−/− versus WT mice as indicated by lower colonic numbers of neutrophils in the former. Conversely, adaptive immune cell counts including T lymphocytes were higher in large intestines of NOD2^−/− as compared to WT mice that were paralleled by increased colonic IL-6 secretion and higher TNF and IL-18 mRNA expression levels in large intestines of the former. Only in NOD2^−/− mice, however, colonic IL-22 mRNA expression was down-regulated at day 14 p.i. Whereas viable commensal intestinal bacteria could exclusively be detected in mesenteric lymph nodes and livers of NOD2^−/− mice, bacterial translocation rates to kidneys and spleen were NOD2 independent. Notably, large intestinal mRNA expression levels of mucin-2, constituting a pivotal factor involved in epithelial barrier integrity, were comparable in naive and C. jejuni infected mice of either genotype.

Conclusion

NOD2 is involved in the well-balanced regulation of innate and adaptive pro-inflammatory immune responses of conventional mice upon C. jejuni infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0155-3) contains supplementary material, which is available to authorized users.

The Role of IL-23, IL-22, and IL-18 in Campylobacter Jejuni Infection of Conventional Infant Mice

We have recently shown that, within 1 week following peroral Campylobacter jejuni infection, conventional infant mice develop self-limiting enteritis. We here investigated the role of IL-23, IL-22, and IL-18 during C. jejuni strain 81-176 infection of infant mice. The pathogen efficiently colonized the intestines of IL-18(-/-) mice only, but did not translocate to extra-intestinal compartments. At day 13 postinfection (p.i.), IL-22(-/-) mice displayed lower colonic epithelial apoptotic cell numbers as compared to wildtype mice, whereas, conversely, colonic proliferating cells increased in infected IL-22(-/-) and IL-18(-/-) mice. At day 6 p.i., increases in neutrophils, T and B lymphocytes were less pronounced in gene-deficient mice, whereas regulatory T cell numbers were lower in IL-23p19(-/-) and IL-22(-/-) as compared to wildtype mice, which was accompanied by increased colonic IL-10 levels in the latter. Until then, colonic pro-inflammatory cytokines including TNF, IFN-γ, IL-6, and MCP-1 increased in IL-23p19(-/-) mice, whereas IL-18(-/-) mice exhibited decreased cytokine levels and lower colonic numbers of T and B cell as well as of neutrophils, macrophages, and monocytes as compared to wildtype controls. In conclusion, IL-23, IL-22, and IL-18 are differentially involved in mediating C. jejuni-induced immunopathology of conventional infant mice.

Toll-Like Receptor-4 Dependent Intestinal Gene Expression During Arcobacter Butzleri Infection of Gnotobiotic Il-10 Deficient Mice

We have previously shown that Arcobacter butzleri infection induces Toll-like receptor (TLR) -4 dependent immune responses in perorally infected gnotobiotic IL-10^–/– mice. Here, we analyzed TLR-4-dependent expression of genes encoding inflammatory mediators and matrix-degrading gelatinases MMP-2 and -9 in the small and large intestines of gnotobiotic TLR-4-deficient IL-10^–/– mice that were perorally infected with A. butzleri strains CCUG 30485 or C1, of human and chicken origin, respectively. At day 6 following A. butzleri infection, colonic mucin-2 mRNA, as integral part of the intestinal mucus layer, was downregulated in the colon, but not ileum, of IL-10^–/– but not TLR-4^–/– IL-10^–/– mice. CCUG 30485 strain-infected TLR-4-deficient IL-10^–/– mice displayed less distinctly upregulated IFN-γ, IL-17A, and IL-1β mRNA levels in ileum and colon, which was also true for colonic IL-22. These changes were accompanied by upregulated colonic MMP-2 and ileal MMP-9 mRNA exclusively in IL-10^–/– mice. In conclusion, TLR-4 is essentially involved in A. butzleri mediated modulation of gene expression in the intestines of gnotobiotic IL-10^–/– mice.

Probiotics: a proactive approach to health. A symposium report

This report summarises talks given at the 8th International Yakult Symposium, held on 23-24 April 2015 in Berlin. Two presentations explored different aspects of probiotic intervention: the small intestine as a probiotic target and inclusion of probiotics into integrative approaches to gastroenterology. Probiotic recommendations in gastroenterology guidelines and current data on probiotic efficacy in paediatric patients were reviewed. Updates were given on probiotic and gut microbiota research in obesity and obesity-related diseases, the gut-brain axis and development of psychobiotics, and the protective effects of equol-producing strains for prostate cancer. Recent studies were presented on probiotic benefit for antibiotic-associated diarrhoea and people with HIV, as well as protection against the adverse effects of a short-term high-fat diet. Aspects of probiotic mechanisms of activity were discussed, including immunomodulatory mechanisms and metabolite effects, the anti-inflammatory properties of Faecalibacterium prausnitzii, the relationship between periodontitis, microbial production of butyrate in the oral cavity and ageing, and the pathogenic mechanisms of Campylobacter. Finally, an insight was given on a recent expert meeting, which re-examined the probiotic definition, advised on the appropriate use and scope of the term and outlined different probiotic categories and the prevalence of different mechanisms of activity.

Anti-Inflammatory Properties of NAP in Acute Toxoplasma Gondii-Induced Ileitis in Mice

The octapeptide NAP has been shown to exert neuroprotective properties. Here, we investigated potential anti-inflammatory effects of NAP in an acute ileitis model. To address this, C57BL/6j mice were perorally infected with Toxoplasma gondii (day 0). Within 1 week postinfection (p.i.), placebo (PLC)-treated mice developed acute ileitis due to Th1-type immune responses. Mice that were subjected to intraperitoneal NAP treatment from day 1 until day 6 p.i., however, developed less distinct macroscopic and microscopic disease as indicated by less body weight loss, less distinct histopathological ileal changes, and lower ileal apoptotic, but higher proliferating cell numbers, less abundance of neutrophils, macrophages, monocytes, and T lymphocytes, but higher numbers of regulatory T cells in the ileal mucosa and lamina propria, and lower concentrations of pro-inflammatory mediators in the ilea as compared to PLC controls at day 7 p.i. Remarkably, NAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments including liver and spleen. Strikingly, lower MCP-1, TNF, and IL-12p70 serum concentrations in NAP as compared to PLC-treated mice at day 7 p.i. indicate a pronounced systemic anti-inflammatory effect of NAP in acute ileitis. These findings provide first evidence for NAP as a potential novel treatment option in intestinal inflammation.

Obese-type gut microbiota induce neurobehavioral changes in the absence of obesity

BACKGROUND

The prevalence of mental illness, particularly depression and dementia, is increased by obesity. Here, we test the hypothesis that obesity-associated changes in gut microbiota are intrinsically able to impair neurocognitive behavior in mice.

METHODS

Conventionally housed, nonobese, adult male C57BL/6 mice maintained on a normal chow diet were subjected to a microbiome depletion/transplantation paradigm using microbiota isolated from donors on either a high-fat diet (HFD) or control diet. Following re-colonization, mice were subjected to comprehensive behavioral and biochemical analyses.

RESULTS

The mice given HFD microbiota had significant and selective disruptions in exploratory, cognitive, and stereotypical behavior compared with mice with control diet microbiota in the absence of significant differences in body weight. Sequencing-based phylogenetic analysis confirmed the presence of distinct core microbiota between groups, with alterations in α- and β-diversity, modulation in taxonomic distribution, and statistically significant alterations to metabolically active taxa. HFD microbiota also disrupted markers of intestinal barrier function, increased circulating endotoxin, and increased lymphocyte expression of ionized calcium-binding adapter molecule 1, toll-like receptor 2, and toll-like receptor 4. Finally, evaluation of brain homogenates revealed that HFD-shaped microbiota increased neuroinflammation and disrupted cerebrovascular homeostasis.

CONCLUSIONS

Collectively, these data reinforce the link between gut dysbiosis and neurologic dysfunction and suggest that dietary and/or pharmacologic manipulation of gut microbiota could attenuate the neurologic complications of obesity.

Pituitary adenylate cyclase-activating polypeptide ameliorates experimental acute ileitis and extra-intestinal sequelae

Background

The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) plays pivotal roles in immunity and inflammation. So far, potential immune-modulatory properties of PACAP have not been investigated in experimental ileitis.

Methodology/Principal Findings

Mice were perorally infected with Toxoplasma (T.) gondii to induce acute ileitis (day 0) and treated daily with synthetic PACAP38 from day 1 to 6 post infection (p.i.; prophylaxis) or from day 4 to 6 p.i. (therapy). Whereas placebo-treated control mice suffered from acute ileitis at day 7 p.i. and succumbed to infection, intestinal immunopathology was ameliorated following PACAP prophylaxis. PACAP-treated mice exhibited increased abundance of small intestinal FOXP3+ cells, but lower numbers of ileal T lymphocytes, neutrophils, monocytes and macrophages, which was accompanied by less ileal expression of pro-inflammatory cytokines such as IL-23p19, IL-22, IFN-γ, and MCP-1. Furthermore, PACAP-treated mice displayed higher anti-inflammatory IL-4 concentrations in mesenteric lymph nodes and liver and higher systemic anti-inflammatory IL-10 levels in spleen and serum as compared to control animals at day 7 p.i. Remarkably, PACAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments as indicated by reduced pro-inflammatory mediator levels in spleen (TNF-α, nitric oxide) and liver (TNF-α, IFN-γ, MCP-1, IL-6) and less severe histopathological sequelae in lungs and kidneys following prophylactic PACAP treatment. Strikingly, PACAP prolonged survival of T. gondii infected mice in a time-of-treatment dependent manner.

Conclusion/Significance

Synthetic PACAP ameliorates acute small intestinal inflammation and extra-intestinal sequelae by down-regulating Th1-type immunopathology, reducing oxidative stress and up-regulating anti-inflammatory cytokine responses. These findings provide novel potential treatment options of inflammatory bowel diseases.

Nucleotide-oligomerization-domain-2 affects commensal gut microbiota composition and intracerebral immunopathology in acute Toxoplasma gondii induced murine ileitis

Background

Within one week following peroral high dose infection with Toxoplasma (T.) gondii, susceptible mice develop non-selflimiting acute ileitis due to an underlying Th1-type immunopathology. The role of the innate immune receptor nucleotide-oligomerization-domain-2 (NOD2) in mediating potential extra-intestinal inflammatory sequelae including the brain, however, has not been investigated so far.

Methodology/Principal Findings

Following peroral infection with 100 cysts of T. gondii strain ME49, NOD2^-/- mice displayed more severe ileitis and higher small intestinal parasitic loads as compared to wildtype (WT) mice. However, systemic (i.e. splenic) levels of pro-inflammatory cytokines such as TNF-α and IFN-γ were lower in NOD2^-/- mice versus WT controls at day 7 p.i. Given that the immunopathological outcome might be influenced by the intestinal microbiota composition, which is shaped by NOD2, we performed a quantitative survey of main intestinal bacterial groups by 16S rRNA analysis. Interestingly, Bifidobacteria were virtually absent in NOD2^-/- but not WT mice, whereas differences in remaining bacterial species were rather subtle. Interestingly, more distinct intestinal inflammation was accompanied by higher bacterial translocation rates to extra-intestinal tissue sites such as liver, spleen, and kidneys in T. gondii infected NOD2^-/- mice. Strikingly, intracerebral inflammatory foci could be observed as early as seven days following T. gondii infection irrespective of the genotype of animals, whereas NOD2^-/- mice exhibited higher intracerebral parasitic loads, higher F4/80 positive macrophage and microglia numbers as well as higher IFN-γ mRNA expression levels as compared to WT control animals.

Conclusion/Significance

NOD2 signaling is involved in protection of mice from T. gondii induced acute ileitis. The parasite-induced Th1-type immunopathology at intestinal as well as extra-intestinal sites including the brain is modulated in a NOD2-dependent manner.

A novel mouse model of Campylobacter jejuni gastroenteritis reveals key pro-inflammatory and tissue protective roles for Toll-like receptor signaling during infection

Campylobacter jejuni is a major source of foodborne illness in the developed world, and a common cause of clinical gastroenteritis. Exactly how C. jejuni colonizes its host's intestines and causes disease is poorly understood. Although it causes severe diarrhea and gastroenteritis in humans, C. jejuni typically dwells as a commensal microbe within the intestines of most animals, including birds, where its colonization is asymptomatic. Pretreatment of C57BL/6 mice with the antibiotic vancomycin facilitated intestinal C. jejuni colonization, albeit with minimal pathology. In contrast, vancomycin pretreatment of mice deficient in SIGIRR (Sigirr^−/−), a negative regulator of MyD88-dependent signaling led to heavy and widespread C. jejuni colonization, accompanied by severe gastroenteritis involving strongly elevated transcription of Th1/Th17 cytokines. C. jejuni heavily colonized the cecal and colonic crypts of Sigirr^−/− mice, adhering to, as well as invading intestinal epithelial cells. This infectivity was dependent on established C. jejuni pathogenicity factors, capsular polysaccharides (kpsM) and motility/flagella (flaA). We also explored the basis for the inflammatory response elicited by C. jejuni in Sigirr^−/− mice, focusing on the roles played by Toll-like receptors (TLR) 2 and 4, as these innate receptors were strongly stimulated by C. jejuni. Despite heavy colonization, Tlr4^−/−/Sigirr^−/− mice were largely unresponsive to infection by C. jejuni, whereas Tlr2^−/−/Sigirr^−/− mice developed exaggerated inflammation and pathology. This indicates that TLR4 signaling underlies the majority of the enteritis seen in this model, whereas TLR2 signaling had a protective role, acting to promote mucosal integrity. Furthermore, we found that loss of the C. jejuni capsule led to increased TLR4 activation and exaggerated inflammation and gastroenteritis. Together, these results validate the use of Sigirr^−/− mice as an exciting and relevant animal model for studying the pathogenesis and innate immune responses to C. jejuni.

Research into the key virulence strategies of the bacterial pathogen Campylobacter jejuni, as well as the host immune responses that develop against this microbe have, in many ways, been limited by the lack of relevant animal models. Here we describe the use of Sigirr deficient (^−/−) mice as a model for C. jejuni pathogenesis. Not only do Sigirr^−/− mice develop significant intestinal inflammation in response to colonization by C. jejuni, but the ability of this pathogen to trigger gastroenteritis was dependent on key virulence factors. We also found that the induction of the inflammatory and Th1/Th17 immune responses to infection in these mice depended on specific Toll-like receptors, principally TLR4, which we identified as the main driver of inflammation. In contrast, TLR2 signaling was found to protect mucosal integrity, with Tlr2^−/−/Sigirr^−/− mice suffering exaggerated mucosal damage and inflammation. Notably, we found that C. jejuni's capsule helped conceal it from the host's immune system as its loss led to significantly increased activation of host TLRs and exaggerated gastroenteritis. Our research shows that the increased sensitivity of Sigirr^−/− mice can be used to generate a unique and exciting model that facilitates the study of C. jejuni pathogenesis as well as host immunity to this enteric pathogen.

The impact of Toll-like-receptor-9 on intestinal microbiota composition and extra-intestinal sequelae in experimental Toxoplasma gondii induced ileitis

Background

Following peroral Toxoplasma (T.) gondii infection, susceptible mice develop acute ileitis due to a microbiota-dependent Th1 type immunopathology. Toll-like-receptor (TLR)-9 is known to recognize bacterial DNA and mediates intestinal inflammation, but its impact on intestinal microbiota composition and extra-intestinal sequelae following T. gondii infection has not yet been elucidated.

Methods and results

Seven days following peroral infection (p.i.) with 100 cysts of T. gondii ME49 strain, TLR-9^-/- and wildtype (WT) mice suffered from comparable ileitis, whereas ileal parasitic loads as well as IFN-γ and nitric oxide levels were higher in TLR-9^-/- compared to WT mice. Locally, TLR-9^-/- mice exhibited increased ileal CD3+, but not FOXP3+ cell numbers at day 7 p.i.; in mesenteric lymph nodes IFN-γ-producing CD4+ cell numbers and TNF-α and IFN-γ concentrations were also increased in TLR-9^-/- compared to WT mice. T. gondii DNA levels, however, did not differ in mice of either genotype. Differences in intestinal microbiota were rather subtle except for bifidobacteria that were virtually absent in both, naïve and T. gondii infected TLR-9^-/-, but not WT mice. Extra-intestinally, TLR-9^-/- mice displayed less distinct systemic immune responses as indicated by lower serum IL-6, and splenic TNF-α and IFN-γ levels as compared to WT mice despite higher translocation rates of intestinal bacteria to extra-intestinal compartments such as liver, spleen, kidney, and cardiac blood. Most importantly, brains were also affected in this inflammatory scenario as early as day 7 p.i. Remarkably, TLR-9^-/- mice exhibited more pronounced inflammatory infiltrates with higher numbers of F4/80+ macrophages and microglia in the cortex and meninges as compared to WT mice, whereas T. gondii DNA levels did not differ.

Conclusion

We here show that TLR-9 is not required for the development of T. gondii induced ileitis but mediates distinct inflammatory changes in intestinal and extra-intestinal compartments including the brain.

Colonization resistance against genetically modified Escherichia coli K12 (W3110) strains is abrogated following broad-spectrum antibiotic treatment and acute ileitis

Escherichia coli K12 (EcK12) is commonly used for gene technology purposes and regarded as a security strain due to its inability to adhere to epithelial cells. The conventional intestinal microbiota composition is critical for physiological colonization resistance against most bacterial species including pathogens. We were therefore interested whether intestinal colonization by a genetically modified EcK12 (W3110) strain carrying a chloramphenicol resistance cassette was facilitated following broad-spectrum antibiotic treatment eradicating the intestinal microbiota or induction of small intestinal inflammation accompanied by distinct microbiota shifts. Whereas conventional C57BL/6 and BALB/c mice had virtually expelled the EcK12 (W3110) strain within the first 3 days upon peroral infection, EcK12 (W3110) could establish within the small and large intestines of gnotobiotic mice generated by quintuple antibiotic treatment. Gnotobiotic mice perorally infected with EcK12 (W3110) plus fecal transplant from conventional donors harbored lower intestinal EcK12 (W3110) loads compared to animals challenged with EcK12 (W3110) alone. Furthermore, EcK12 (W3110) infection of conventional mice after but not before induction of ileitis resulted in stable colonization of ileum and colon by EcK12 (W3110). Taken together, broad-spectrum antibiotic treatment and intestinal inflammation compromise colonization resistance and thus facilitate colonization of the intestinal tract with genetically modified EcK12 security strains.