Impact of Campylobacter jejuni cj0268c knockout mutation on intestinal colonization, translocation, and induction of immunopathology in gnotobiotic IL-10 deficient mice

Flotillin-mediated stabilization of unfolded proteins in bacterial membrane microdomains

The function of many bacterial processes depends on the formation of functional membrane microdomains (FMMs), which resemble the lipid rafts of eukaryotic cells. However, the mechanism and the biological function of these membrane microdomains remain unclear. Here, we show that FMMs in the pathogen methicillin-resistant Staphylococcus aureus (MRSA) are dedicated to confining and stabilizing proteins unfolded due to cellular stress. The FMM scaffold protein flotillin forms a clamp-shaped oligomer that holds unfolded proteins, stabilizing them and favoring their correct folding. This process does not impose a direct energy cost on the cell and is crucial to survival of ATP-depleted bacteria, and thus to pathogenesis. Consequently, FMM disassembling causes the accumulation of unfolded proteins, which compromise MRSA viability during infection and cause penicillin re-sensitization due to PBP2a unfolding. Thus, our results indicate that FMMs mediate ATP-independent stabilization of unfolded proteins, which is essential for bacterial viability during infection.

Metabolomic signatures of intestinal colonization resistance against Campylobacter jejuni in mice

Introduction

Campylobacter jejuni stands out as one of the leading causes of bacterial enteritis. In contrast to humans, specific pathogen-free (SPF) laboratory mice display strict intestinal colonization resistance (CR) against C. jejuni, orchestrated by the specific murine intestinal microbiota, as shown by fecal microbiota transplantation (FMT) earlier.

Methods

Murine infection models, comprising SPF, SAB, hma, and mma mice were employed. FMT and microbiota depletion were confirmed by culture and culture-independent analyses. Targeted metabolome analyses of fecal samples provided insights into the associated metabolomic signatures.

Results

In comparison to hma mice, the murine intestinal microbiota of mma and SPF mice (with CR against C. jejuni) contained significantly elevated numbers of lactobacilli, and Mouse Intestinal Bacteroides, whereas numbers of enterobacteria, enterococci, and Clostridium coccoides group were reduced. Targeted metabolome analysis revealed that fecal samples from mice with CR contained increased levels of secondary bile acids and fatty acids with known antimicrobial activities, but reduced concentrations of amino acids essential for C. jejuni growth as compared to control animals without CR.

Discussion

The findings highlight the role of microbiota-mediated nutrient competition and antibacterial activities of intestinal metabolites in driving murine CR against C. jejuni. The study underscores the complex dynamics of host-microbiota-pathogen interactions and sets the stage for further investigations into the mechanisms driving CR against enteric infections.

Molecular structures mediating adhesion of Campylobacter jejuni to abiotic and biotic surfaces

Microaerophilic, Gram-negative Campylobacter jejuni is the causative agent of campylobacteriosis, the most common bacterial gastrointestinal infection worldwide. Adhesion is the crucial first step in both infection or interaction with the host and biofilm formation, and is a critical factor for bacterial persistence. Here we describe the proteins and other surface structures that promote adhesion to various surfaces, including abiotic surfaces, microorganisms, and animal and human hosts. In addition, we provide insight into the distribution of adhesion proteins among strains from different ecological niches and highlight unexplored proteins involved in C. jejuni adhesion. Protein-protein, protein-glycan, and glycan-glycan interactions are involved in C. jejuni adhesion, with different factors contributing to adhesion to varying degrees under different circumstances. As adhesion is essential for survival and persistence, it represents an interesting target for C. jejuni control. Knowledge of the adhesion process is incomplete, as different molecular and functional aspects have been studied for different structures involved in adhesion. Therefore, it is important to strive for an integration of different approaches to obtain a clearer picture of the adhesion process on different surfaces and to consider the involvement of proteins, glycoconjugates, and polysaccharides and their cooperation.

Mouse models for bacterial enteropathogen infections: insights into the role of colonization resistance

Globally, enteropathogenic bacteria are a major cause of morbidity and mortality.1-3 Campylobacter, Salmonella, Shiga-toxin-producing Escherichia coli, and Listeria are among the top five most commonly reported zoonotic pathogens in the European Union.4 However, not all individuals naturally exposed to enteropathogens go on to develop disease. This protection is attributable to colonization resistance (CR) conferred by the gut microbiota, as well as an array of physical, chemical, and immunological barriers that limit infection. Despite their importance for human health, a detailed understanding of gastrointestinal barriers to infection is lacking, and further research is required to investigate the mechanisms that underpin inter-individual differences in resistance to gastrointestinal infection. Here, we discuss the current mouse models available to study infections by non-typhoidal Salmonella strains, Citrobacter rodentium (as a model for enteropathogenic and enterohemorrhagic E. coli), Listeria monocytogenes, and Campylobacter jejuni. Clostridioides difficile is included as another important cause of enteric disease in which resistance is dependent upon CR. We outline which parameters of human infection are recapitulated in these mouse models, including the impact of CR, disease pathology, disease progression, and mucosal immune response. This will showcase common virulence strategies, highlight mechanistic differences, and help researchers from microbiology, infectiology, microbiome research, and mucosal immunology to select the optimal mouse model.

Murine Models for the Investigation of Colonization Resistance and Innate Immune Responses in Campylobacter Jejuni Infections

Human infections with the food-borne pathogen Campylobacter jejuni are progressively increasing worldwide and constitute a significant socioeconomic burden to mankind. Intestinal campylobacteriosis in humans is characterized by bloody diarrhea, fever, abdominal pain, and severe malaise. Some individuals develop chronic post-infectious sequelae including neurological and autoimmune diseases such as reactive arthritis and Guillain-Barré syndrome. Studies unraveling the molecular mechanisms underlying campylobacteriosis and post-infectious sequelae have been hampered by the scarcity of appropriate experimental in vivo models. Particularly, conventional laboratory mice are protected from C. jejuni infection due to the physiological colonization resistance exerted by the murine gut microbiota composition. Additionally, as compared to humans, mice are up to 10,000 times more resistant to C. jejuni lipooligosaccharide (LOS) constituting a major pathogenicity factor responsible for the immunopathological host responses during campylobacteriosis. In this chapter, we summarize the recent progress that has been made in overcoming these fundamental obstacles in Campylobacter research in mice. Modification of the murine host-specific gut microbiota composition and sensitization of the mice to C. jejuni LOS by deletion of genes encoding interleukin-10 or a single IL-1 receptor-related molecule as well as by dietary zinc depletion have yielded reliable murine infection models resembling key features of human campylobacteriosis. These substantial improvements pave the way for a better understanding of the molecular mechanisms underlying pathogen-host interactions. The ongoing validation and standardization of these novel murine infection models will provide the basis for the development of innovative treatment and prevention strategies to combat human campylobacteriosis and collateral damages of C. jejuni infections.

Toll-Like Receptor-4 Is Involved in Mediating Intestinal and Extra-Intestinal Inflammation in Campylobacter coli-Infected Secondary Abiotic IL-10-/- Mice

Human Campylobacter infections are emerging worldwide and constitute significant health burdens. We recently showed that the immunopathological sequelae in Campylobacter jejuni-infected mice were due to Toll-like receptor (TLR)-4 dependent immune responses induced by bacterial lipooligosaccharide (LOS). Information regarding the molecular mechanisms underlying Campylobacter coli-host interactions are scarce, however. Therefore, we analyzed C. coli-induced campylobacteriosis in secondary abiotic IL-10^−/− mice with and without TLR4. Mice were infected perorally with a human C. coli isolate or with a murine commensal Escherichia coli as apathogenic, non-invasive control. Independent from TLR4, C. coli and E. coli stably colonized the gastrointestinal tract, but only C. coli induced clinical signs of campylobacteriosis. TLR4^−/− IL-10^−/− mice, however, displayed less frequently fecal blood and less distinct histopathological and apoptotic sequelae in the colon versus IL-10^−/− counterparts on day 28 following C. coli infection. Furthermore, C. coli-induced colonic immune cell responses were less pronounced in TLR4^−/− IL-10^−/− as compared to IL-10^−/− mice and accompanied by lower pro-inflammatory mediator concentrations in the intestines and the liver of the former versus the latter. In conclusion, our study provides evidence that TLR4 is involved in mediating C. coli-LOS-induced immune responses in intestinal and extra-intestinal compartments during murine campylobacteriosis.

Pituitary Adenylate Cyclase-Activating Polypeptide Alleviates Intestinal, Extra-Intestinal and Systemic Inflammatory Responses during Acute Campylobacter jejuni-induced Enterocolitis in Mice

Human Campylobacter jejuni infections are emerging, and constitute a significant health burden worldwide. The ubiquitously expressed pituitary adenylate cyclase-activating polypeptide (PACAP) is well-known for its cell-protective and immunomodulatory effects. In our actual intervention study, we used an acute campylobacteriosis model and assessed the potential disease-alleviating effects of exogenous PACAP. Therefore, secondary abiotic IL-10^-/- mice were perorally infected with C. jejuni and treated with synthetic PACAP38 intraperitoneally from day 2 until day 5 post-infection. Whereas PACAP did not interfere with the gastrointestinal colonization of the pathogen, mice from the PACAP group exhibited less severe clinical signs of C. jejuni-induced disease, as compared to mock controls, which were paralleled by alleviated apoptotic, but enhanced cell proliferative responses in colonic epithelia on day 6 post-infection. Furthermore, PACAP dampened the accumulation of macrophages and monocytes, but enhanced regulatory T cell responses in the colon, which were accompanied by less IFN-γ secretion in intestinal compartments in PACAP versus mock-treated mice. Remarkably, the inflammation-dampening properties of PACAP could also be observed in extra-intestinal organs, and strikingly, even the systemic circulation on day 6 post-infection. For the first time, we provide evidence that synthetic PACAP might be a promising candidate to combat acute campylobacteriosis and post-infectious sequelae.

The Host-Specific Intestinal Microbiota Composition Impacts Campylobacter coli Infection in a Clinical Mouse Model of Campylobacteriosis

Human Campylobacter-infections are progressively rising globally. However, the molecular mechanisms underlying C. coli–host interactions are incompletely understood. In this study, we surveyed the impact of the host-specific intestinal microbiota composition during peroral C. coli infection applying an established murine campylobacteriosis model. Therefore, microbiota-depleted IL-10^−/− mice were subjected to peroral fecal microbiota transplantation from murine versus human donors and infected with C. coli one week later by gavage. Irrespective of the microbiota, C. coli stably colonized the murine gastrointestinal tract until day 21 post-infection. Throughout the survey, C. coli-infected mice with a human intestinal microbiota displayed more frequently fecal blood as their murine counterparts. Intestinal inflammatory sequelae of C. coli-infection could exclusively be observed in mice with a human intestinal microbiota, as indicated by increased colonic numbers of apoptotic epithelial cells and innate as well as adaptive immune cell subsets, which were accompanied by more pronounced pro-inflammatory cytokine secretion in the colon and mesenteric lymph nodes versus mock controls. However, in extra-intestinal, including systemic compartments, pro-inflammatory responses upon pathogen challenge could be assessed in mice with either microbiota. In conclusion, the host-specific intestinal microbiota composition has a profound effect on intestinal and systemic pro-inflammatory immune responses during C. coli infection.

Inflammatory Immune Responses and Gut Microbiota Changes Following Campylobacter coli Infection of IL-10-/- Mice with Chronic Colitis

Human infections with the food-borne enteropathogens Campylobacter are progressively rising. Recent evidence revealed that pre-existing intestinal inflammation facilitates enteropathogenic infection subsequently exacerbating the underlying disease. Given that only little is known about C. coli-host interactions and particularly during intestinal inflammation, the aim of the present study was to survey gastrointestinal colonization properties, gut microbiota changes and pro-inflammatory sequelae upon peroral C. coli-infection of IL-10^-/- mice with chronic colitis. C. coli colonized the gastrointestinal tract of mice with varying efficiencies until day 28 post-infection and induced macroscopic and microscopic inflammatory changes as indicated by shorter colonic lengths, more distinct histopathological changes in the colonic mucosa and higher numbers of apoptotic colonic epithelial cells when compared to mock-infected controls. Furthermore, not only colonic innate and adaptive immune cell responses, but also enhanced systemic TNF-α secretion could be observed following C. coli as opposed to mock challenge. Notably, C. coli induced intestinal inflammatory sequelae were accompanied with gut microbiota shifts towards higher commensal enterobacterial loads in the infected gut lumen. Moreover, the pathogen translocated from the intestinal tract to extra-intestinal tissue sites in some cases, but never to systemic compartments. Hence, C. coli accelerates inflammatory immune responses in IL-10^-/- mice with chronic colitis.

Toll-Like Receptor-4 Dependent Intestinal and Systemic Sequelae Following Peroral Campylobacter coli Infection of IL10 Deficient Mice Harboring a Human Gut Microbiota

Zoonotic Campylobacter, including C. jejuni and C. coli, are among the most prevalent agents of food-borne enteritis worldwide. The immunopathological sequelae of campylobacteriosis are caused by Toll-like Receptor-4 (TLR4)-dependent host immune responses, induced by bacterial lipooligosaccharide (LOS). In order to investigate C. coli-host interactions, including the roles of the human gut microbiota and TLR4, upon infection, we applied a clinical acute campylobacteriosis model, and subjected secondary abiotic, TLR4-deficient IL10-/- mice and IL10-/- controls to fecal microbiota transplantation derived from human donors by gavage, before peroral C. coli challenge. Until day 21 post-infection, C. coli could stably colonize the gastrointestinal tract of human microbiota-associated (hma) mice of either genotype. TLR4-deficient IL10-/- mice, however, displayed less severe clinical signs of infection, that were accompanied by less distinct apoptotic epithelial cell and innate as well as adaptive immune cell responses in the colon, as compared to IL10-/- counterparts. Furthermore, C. coli infected IL10-/-, as opposed to TLR4-deficient IL10-/-, mice displayed increased pro-inflammatory cytokine concentrations in intestinal and, strikingly, systemic compartments. We conclude that pathogenic LOS might play an important role in inducing TLR4-dependent host immune responses upon C. coli infection, which needs to be further addressed in more detail.

Virulence Traits of Inpatient Campylobacter jejuni Isolates, and a Transcriptomic Approach to Identify Potential Genes Maintaining Intracellular Survival

There are still major gaps in our understanding of the bacterial factors that influence the outcomes of human Campylobacter jejuni infection. The aim of this study was to compare the virulence-associated features of 192 human C. jejuni strains isolated from hospitalized patients with diarrhoea (150/192, 78.1%), bloody diarrhoea (23/192, 11.9%), gastroenteritis (3/192, 1.6%), ulcerative colitis (3/192, 1.5%), and stomach ache (2/192, 1.0%). Traits were analysed with genotypic and phenotypic methods, including PCR and extracellular matrix protein (ECMP) binding, adhesion, and invasion capacities. Results were studied alongside patient symptoms, but no distinct links with them could be determined. Since the capacity of C. jejuni to invade host epithelial cells is one of its most enigmatic attributes, a high throughput transcriptomic analysis was performed in the third hour of internalization with a C. jejuni strain originally isolated from bloody diarrhoea. Characteristic groups of genes were significantly upregulated, outlining a survival strategy of internalized C. jejuni comprising genes related (1) to oxidative stress; (2) to a protective sheath formed by the capsule, LOS, N-, and O- glycosylation systems; (3) to dynamic metabolic activity supported by different translocases and the membrane-integrated component of the flagellar apparatus; and (4) to hitherto unknown genes.

Novel Clinical Campylobacter jejuni Infection Models Based on Sensitization of Mice to Lipooligosaccharide, a Major Bacterial Factor Triggering Innate Immune Responses in Human Campylobacteriosis

: Human Campylobacter jejuni infections inducing campylobacteriosis including post-infectious sequelae such as Guillain-Barré syndrome and reactive arthritis are rising worldwide and progress into a global burden of high socioeconomic impact. Intestinal immunopathology underlying campylobacteriosis is a classical response of the innate immune system characterized by the accumulation of neutrophils and macrophages which cause tissue destruction, barrier defects and malabsorption leading to bloody diarrhea. Clinical studies revealed that enteritis and post-infectious morbidities of human C. jejuni infections are strongly dependent on the structure of pathogenic lipooligosaccharides (LOS) triggering the innate immune system via Toll-like-receptor (TLR)-4 signaling. Compared to humans, mice display an approximately 10,000 times weaker TLR-4 response and a pronounced colonization resistance (CR) against C. jejuni maintained by the murine gut microbiota. In consequence, investigations of campylobacteriosis have been hampered by the lack of experimental animal models. We here summarize recent progress made in the development of murine C. jejuni infection models that are based on the abolishment of CR by modulating the murine gut microbiota and by sensitization of mice to LOS. These advances support the major role of LOS driven innate immunity in pathogenesis of campylobacteriosis including post-infectious autoimmune diseases and promote the preclinical evaluation of novel pharmaceutical strategies for prophylaxis and treatment.

Vitamin C alleviates acute enterocolitis in Campylobacter jejuni infected mice

Human foodborne infections with the zoonotic pathogen Campylobacter jejuni are on the rise and constitute a significant socioeconomic burden worldwide. The health-beneficial, particularly anti-inflammatory effects of vitamin C (ascorbate) are well known. In our preclinical intervention study, we assessed potential anti-pathogenic and immunomodulatory effects of ascorbate in C. jejuni-infected secondary abiotic IL-10-/- mice developing acute campylobacteriosis similar to humans. Starting 4 days prior peroral C. jejuni-infection, mice received synthetic ascorbate via the drinking water until the end of the experiment. At day 6 post-infection, ascorbate-treated mice harbored slightly lower colonic pathogen loads and suffered from less severe C. jejuni-induced enterocolitis as compared to placebo control animals. Ascorbate treatment did not only alleviate macroscopic sequelae of infection, but also dampened apoptotic and inflammatory immune cell responses in the intestines that were accompanied by less pronounced pro-inflammatory cytokine secretion. Remarkably, the anti-inflammatory effects of ascorbate pretreatment in C. jejuni-infected mice were not restricted to the intestinal tract but could also be observed in extra-intestinal compartments including liver, kidneys and lungs. In conclusion, due to the potent anti-inflammatory effects observed in the clinical murine C. jejuni-infection model, ascorbate constitutes a promising novel option for prophylaxis and treatment of acute campylobacteriosis.

Carvacrol ameliorates acute campylobacteriosis in a clinical murine infection model

BACKGROUND

The prevalence of human infections with the zoonotic pathogen Campylobacter jejuni is rising worldwide. Therefore, the identification of compounds with potent anti-pathogenic and anti-inflammatory properties for future therapeutic and/or preventive application to combat campylobacteriosis is of importance for global health. Results of recent studies suggested carvacrol (4-isopropyl-2-methylphenol) as potential candidate molecule for the treatment of campylobacteriosis in humans and for the prevention of Campylobacter colonization in farm animals.

RESULTS

To address this in a clinical murine infection model of acute campylobacteriosis, secondary abiotic IL-10-/- mice were subjected to synthetic carvacrol via the drinking water starting 4 days before peroral C. jejuni challenge. Whereas at day 6 post-infection placebo treated mice suffered from acute enterocolitis, mice from the carvacrol cohort not only harbored two log orders of magnitude lower pathogen loads in their intestines, but also displayed significantly reduced disease symptoms. Alleviated campylobacteriosis following carvacrol application was accompanied by less distinct intestinal apoptosis and pro-inflammatory immune responses as well as by higher numbers of proliferating colonic epithelial cells. Remarkably, the inflammation-ameliorating effects of carvacrol treatment were not restricted to the intestinal tract, but could also be observed in extra-intestinal organs such as liver, kidneys and lungs and, strikingly, systemically as indicated by lower IFN-γ, TNF, MCP-1 and IL-6 serum concentrations in carvacrol versus placebo treated mice. Furthermore, carvacrol treatment was associated with less frequent translocation of viable C. jejuni originating from the intestines to extra-intestinal compartments.

CONCLUSION

The lowered C. jejuni loads and alleviated symptoms observed in the here applied clinical murine model for human campylobacteriosis highlight the application of carvacrol as a promising novel option for both, the treatment of campylobacteriosis and hence, for prevention of post-infectious sequelae in humans, and for the reduction of C. jejuni colonization in the intestines of vertebrate lifestock animals.

Campylobacter concisus Impairs Sodium Absorption in Colonic Epithelium via ENaC Dysfunction and Claudin-8 Disruption

The epithelial sodium channel (ENaC) can increase the colonic absorptive capacity for salt and water. Campylobacter concisus is a common pathogenic epsilonproteobacterium, causing enteritis and diarrhea. It can induce barrier dysfunction in the intestine, but its influence on intestinal transport function is still unknown. Therefore, our study aimed to characterize C. concisus effects on ENaC using the HT-29/B6-GR/MR (epithelial cell line HT-29/B6 transfected with glucocorticoid and mineralocorticoid receptors) cell model and mouse colon. In Ussing chambers, C. concisus infection inhibited ENaC-dependent Na⁺ transport as indicated by a reduction in amiloride-sensitive short circuit current (−55%, n = 15, p < 0.001). This occurred via down-regulation of β- and γ-ENaC mRNA expression and ENaC ubiquitination due to extracellular signal-regulated kinase (ERK)1/2 activation, predicted by Ingenuity Pathway Analysis (IPA). In parallel, C. concisus reduced the expression of the sealing tight junction (TJ) protein claudin-8 and induced claudin-8 redistribution off the TJ domain of the enterocytes, which facilitates the back leakage of Na⁺ ions into the intestinal lumen. In conclusion, C. concisus caused ENaC dysfunction via interleukin-32-regulated ERK1/2, as well as claudin-8-dependent barrier dysfunction—both of which contribute to Na⁺ malabsorption and diarrhea.

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.

Vitamin D in Acute Campylobacteriosis-Results From an Intervention Study Applying a Clinical Campylobacter jejuni Induced Enterocolitis Model

Human Campylobacter infections are progressively rising and of high socioeconomic impact. In the present preclinical intervention study we investigated anti-pathogenic, immuno-modulatory, and intestinal epithelial barrier preserving properties of vitamin D applying an acute campylobacteriosis model. Therefore, secondary abiotic IL-10^−/− mice were perorally treated with synthetic 25-OH-cholecalciferol starting 4 days before peroral Campylobacter jejuni infection. Whereas, 25-OH-cholecalciferol application did not affect gastrointestinal pathogen loads, 25-OH-cholecalciferol treated mice suffered less frequently from diarrhea in the midst of infection as compared to placebo control mice. Moreover, 25-OH-cholecalciferol application dampened C. jejuni induced apoptotic cell responses in colonic epithelia and promoted cell-regenerative measures. At day 6 post-infection, 25-OH-cholecalciferol treated mice displayed lower numbers of colonic innate and adaptive immune cell populations as compared to placebo controls that were accompanied by lower intestinal concentrations of pro-inflammatory mediators including IL-6, MCP1, and IFN-γ. Remarkably, as compared to placebo application synthetic 25-OH-cholecalciferol treatment of C. jejuni infected mice resulted in lower cumulative translocation rates of viable pathogens from the inflamed intestines to extra-intestinal including systemic compartments such as the kidneys and spleen, respectively, which was accompanied by less compromised colonic epithelial barrier function in the 25-OH-cholecalciferol as compared to the placebo cohort. In conclusion, our preclinical intervention study provides evidence that peroral synthetic 25-OH-cholecalciferol application exerts inflammation-dampening effects during acute campylobacteriosis.

Quantification of serine protease HtrA molecules secreted by the foodborne pathogen Campylobacter jejuni

BACKGROUND

Campylobacter jejuni is a major food-borne pathogen and a worldwide health threat. Utilizing different virulence factors, C. jejuni invades the host's intestinal epithelial cell layer. One important factor in this process is the serine protease HtrA, which is secreted into the extracellular space, and helps the bacteria to transmigrate across the gut epithelium by cleaving various cell-cell adhesion proteins. The aim of the present study is to quantify the amount of HtrA molecules secreted per bacterial cell in liquid culture and during infection.

RESULTS

HtrA protein purification and quantitative Western blotting were used to determine the number of HtrA molecules secreted by two C. jejuni model strains, 11168 and 81-176, in liquid culture during an 8-h time course. On average, the two strains yielded similar HtrA secretion rates, with strain 11168 secreting 4314 ± 949 molecules and 81-176 secreting 5483 ± 1246 per bacterium after 2 h. After 8 h, both strains showed a decrease in the average amount of HtrA secreted per bacterial cell over time. Secretion of HtrA by strain 11168 reduced to about 1772 ± 520 molecules and only 2151 ± 562 HtrA molecules were secreted by strain 81-176 at this time point. During infection of gut epithelial cells, the secretion of HtrA is slightly higher with a similar secretion pattern over time compared to culturing in vitro.

CONCLUSION

We determined the number of HtrA molecules secreted by single C. jejuni cells over time. The results suggest that HtrA secretion is regulated in a time-dependent fashion, leading to increasing accumulative HtrA concentrations in the extracellular medium.

Recent Advances in Anti-virulence Therapeutic Strategies With a Focus on Dismantling Bacterial Membrane Microdomains, Toxin Neutralization, Quorum-Sensing Interference and Biofilm Inhibition

Antimicrobial resistance constitutes one of the major challenges facing humanity in the Twenty-First century. The spread of resistant pathogens has been such that the possibility of returning to a pre-antibiotic era is real. In this scenario, innovative therapeutic strategies must be employed to restrict resistance. Among the innovative proposed strategies, anti-virulence therapy has been envisioned as a promising alternative for effective control of the emergence and spread of resistant pathogens. This review presents some of the anti-virulence strategies that are currently being developed, it will cover strategies focused on quench pathogen quorum sensing (QS) systems, disassemble of bacterial functional membrane microdomains (FMMs), disruption of biofilm formation and bacterial toxin neutralization.

Protease Activity of Campylobacter jejuni HtrA Modulates Distinct Intestinal and Systemic Immune Responses in Infected Secondary Abiotic IL-10 Deficient Mice

Even though human Campylobacter jejuni infections are progressively increasing worldwide, the underlying molecular mechanisms of pathogen-host-interactions are still not fully understood. We have recently shown that the secreted serine protease HtrA plays a key role in C. jejuni cellular invasion and transepithelial migration in vitro, and is involved in the onset of intestinal pathology in murine infection models in vivo. In the present study, we investigated whether the protease activity of HtrA had an impact in C. jejuni induced acute enterocolitis. For this purpose, we perorally infected secondary abiotic IL-10^-/- mice with wildtype C. jejuni strain NCTC11168 (11168^WT) or isogenic bacteria carrying protease-inactive HtrA with a single point mutation at S197A in the active center (11168^HtrA-S197A). Irrespective of the applied pathogenic strain, mice harbored similar C. jejuni loads in their feces and exhibited comparably severe macroscopic signs of acute enterocolitis at day 6 postinfection (p.i.). Interestingly, the 11168^HtrA-S197A infected mice displayed less pronounced colonic apoptosis and immune cell responses, but enhanced epithelial proliferation as compared to the 11168^WT strain infected controls. Furthermore, less distinct microscopic sequelae in 11168^HtrA-S197A as compared to parental strain infected mice were accompanied by less distinct colonic secretion of pro-inflammatory cytokines such as MCP-1, IL-6, TNF, and IFN-γ in the former as compared to the latter. Strikingly, the S197A point mutation was additionally associated with less pronounced systemic pro-inflammatory immune responses as assessed in serum samples. In conclusion, HtrA is a remarkable novel virulence determinant of C. jejuni, whose protease activity is not required for intestinal colonization and establishment of disease, but aggravates campylobacteriosis by triggering apoptosis and pro-inflammatory immune responses.

Flotillin scaffold activity contributes to type VII secretion system assembly in Staphylococcus aureus

Scaffold proteins are ubiquitous chaperones that promote efficient interactions between partners of multi-enzymatic protein complexes; although they are well studied in eukaryotes, their role in prokaryotic systems is poorly understood. Bacterial membranes have functional membrane microdomains (FMM), a structure homologous to eukaryotic lipid rafts. Similar to their eukaryotic counterparts, bacterial FMM harbor a scaffold protein termed flotillin that is thought to promote interactions between proteins spatially confined to the FMM. Here we used biochemical approaches to define the scaffold activity of the flotillin homolog FloA of the human pathogen Staphylococcus aureus, using assembly of interacting protein partners of the type VII secretion system (T7SS) as a case study. Staphylococcus aureus cells that lacked FloA showed reduced T7SS function, and thus reduced secretion of T7SS-related effectors, probably due to the supporting scaffold activity of flotillin. We found that the presence of flotillin mediates intermolecular interactions of T7SS proteins. We tested several small molecules that interfere with flotillin scaffold activity, which perturbed T7SS activity in vitro and in vivo. Our results suggest that flotillin assists in the assembly of S. aureus membrane components that participate in infection and influences the infective potential of this pathogen.

The recently discovered functional membrane microdomains (FMM) of prokaryotic cells contain a protein homologous to the scaffold protein flotillin found in eukaryotic lipid rafts. It remains to be elucidated whether, like their eukaryotic counterparts, flotillin homolog proteins have a scaffold function in bacteria. Here we show that the Staphylococcus aureus flotillin FloA acts as a scaffold protein, to promote more efficient assembly of membrane-associated protein interacting partners of multi-enzyme complexes. In a case study, we provide biochemical evidence that FloA participates in assembly of the Type VII secretion system and thus contributes to S. aureus infective potential. Targeted dispersion of FMM-related processes using anti-FMM molecules opens up new perspectives for microbial therapies to treat persistent S. aureus infections.

Membrane Microdomain Disassembly Inhibits MRSA Antibiotic Resistance

A number of bacterial cell processes are confined functional membrane microdomains (FMMs), structurally and functionally similar to lipid rafts of eukaryotic cells. How bacteria organize these intricate platforms and what their biological significance is remain important questions. Using the pathogen methicillin-resistant Staphylococcus aureus (MRSA), we show here that membrane-carotenoid interaction with the scaffold protein flotillin leads to FMM formation, which can be visualized using super-resolution array tomography. These membrane platforms accumulate multimeric protein complexes, for which flotillin facilitates efficient oligomerization. One of these proteins is PBP2a, responsible for penicillin resistance in MRSA. Flotillin mutants are defective in PBP2a oligomerization. Perturbation of FMM assembly using available drugs interferes with PBP2a oligomerization and disables MRSA penicillin resistance in vitro and in vivo, resulting in MRSA infections that are susceptible to penicillin treatment. Our study demonstrates that bacteria possess sophisticated cell organization programs and defines alternative therapies to fight multidrug-resistant pathogens using conventional antibiotics.

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Staphyloxanthin and flotillin preferentially interact and accumulate in FMMs

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FMMs facilitate efficient oligomerization of multimeric protein complexes

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PBP2a, which confers β-lactam resistance on S. aureus, is harbored within FMMs

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FMM disruption disables PBP2a oligomerization and thus, S. aureus antibiotic resistance

Absence of Nucleotide-Oligomerization-Domain-2 Is Associated with Less Distinct Disease in Campylobacter jejuni Infected Secondary Abiotic IL-10 Deficient Mice

Human Campylobacter jejuni-infections are progressively increasing worldwide. Despite their high prevalence and socioeconomic impact the underlying mechanisms of pathogen-host-interactions are only incompletely understood. Given that the innate immune receptor nucleotide-oligomerization-domain-2 (Nod2) is involved in clearance of enteropathogens, we here evaluated its role in murine campylobacteriosis. To address this, we applied Nod2-deficient IL-10-/- (Nod2-/- IL-10-/-) mice and IL-10-/- counterparts both with a depleted intestinal microbiota to warrant pathogen-induced enterocolitis. At day 7 following peroral C. jejuni strain 81-176 infection, Nod2 mRNA was down-regulated in the colon of secondary abiotic IL-10-/- and wildtype mice. Nod2-deficiency did neither affect gastrointestinal colonization nor extra-intestinal and systemic translocation properties of C. jejuni. Colonic mucin-2 mRNA was, however, down-regulated upon C. jejuni-infection of both Nod2-/- IL-10-/- and IL-10-/- mice, whereas expression levels were lower in infected, but also naive Nod2-/- IL-10-/- mice as compared to respective IL-10-/- controls. Remarkably, C. jejuni-infected Nod2-/- IL-10-/- mice were less compromised than IL-10-/- counterparts and displayed less distinct apoptotic, but higher regenerative cell responses in colonic epithelia. Conversely, innate as well as adaptive immune cells such as macrophages and monocytes as well as T lymphocytes and regulatory T-cells, respectively, were even more abundant in large intestines of Nod2-/- IL-10-/- as compared to IL-10-/- mice at day 7 post-infection. Furthermore, IFN-γ concentrations were higher in ex vivo biopsies derived from intestinal compartments including colon and mesenteric lymph nodes as well as in systemic tissue sites such as the spleen of C. jejuni infected Nod2-/- IL-10-/- as compared to IL10-/- counterparts. Whereas, at day 7 postinfection anti-inflammatory IL-22 mRNA levels were up-regulated, IL-18 mRNA was down-regulated in large intestines of Nod2-/- IL-10-/- vs. IL-10-/- mice. In summary, C. jejuni-infection induced less clinical signs and apoptosis, but more distinct colonic pro- and (of note) anti-inflammatory immune as well as regenerative cell responses in Nod2 deficient IL-10-/- as compared to IL-10-/- control mice. We conclude that, even though colonic Nod2 mRNA was down-regulated upon pathogenic challenge, Nod2-signaling is essentially involved in the well-balanced innate and adaptive immune responses upon C. jejuni-infection of secondary abiotic IL-10-/- mice, but does neither impact pathogenic colonization nor translocation.

Small Intestinal Pro-Inflammatory Immune Responses Following Campylobacter Jejuni Infection of Secondary Abiotic IL-10-/- Mice Lacking Nucleotide-Oligomerization-Domain-2

Host immune responses are crucial for combating enteropathogenic infections including Campylobacter jejuni. Within 1 week following peroral C. jejuni infection, secondary abiotic IL-10^–/– mice develop severe immunopathological sequelae affecting the colon (ulcerative enterocolitis). In the present study, we addressed whether pathogen-induced pro-inflammatory immune responses could also be observed in the small intestines dependent on the innate receptor nucleotide-oligomerization-domain-protein 2 (Nod2). Within 7 days following peroral infection, C. jejuni stably colonized the gastrointestinal tract of both IL-10^–/– mice lacking Nod2 (Nod2^–/– IL-10^–/–) and IL-10^–/– controls displaying bloody diarrhea with similar frequencies. Numbers of apoptotic and regenerating epithelial cells increased in the small intestines of C. jejuni-infected mice of either genotype that were accompanied by elevated ileal T and B lymphocyte counts. Notably, ileal T cell numbers were higher in C. jejuni-infected Nod2^–/– IL-10^–/– as compared to IL-10^–/– counterparts. Furthermore, multifold increased concentrations of pro-inflammatory cytokines including IFN-γ, TNF, and MCP-1 could be measured in small intestinal ex vivo biopsies derived from C. jejuni-infected mice of either genotype. In conclusion, C. jejuni-induced pro-inflammatory immune responses affected the small intestines of both Nod2^–/– IL-10^–/– and IL-10^–/– mice, whereas ileal T lymphocyte numbers were even higher in the former.

Immune responses upon Campylobacter jejuni infection of secondary abiotic mice lacking nucleotide-oligomerization-domain-2

Background

Campylobacter jejuni infections are of rising importance worldwide. Given that innate immune receptors including nucleotide-oligomerization-domain-2 (Nod2) are essentially involved in combating enteropathogenic infections, we here surveyed the impact of Nod2 in murine campylobacteriosis.

Methods and results

In order to overcome physiological colonization resistance preventing from C. jejuni infection, we generated secondary abiotic Nod2^−/− and wildtype (WT) mice by broad-spectrum antibiotic treatment. Mice were then perorally infected with C. jejuni strain 81-176 on 2 consecutive days and could be stably colonized by the pathogen at high loads. Notably, Nod2 deficiency did not affect gastrointestinal colonization properties of C. jejuni. Despite high intestinal pathogenic burdens mice were virtually uncompromised and exhibited fecal blood in single cases only. At day 7 postinfection (p.i.) similar increases in numbers of colonic epithelial apoptotic cells could be observed in mice of either genotype, whereas C. jejuni infected Nod2^−/− mice displayed more distinct regenerative properties in the colon than WT controls. C. jejuni infection was accompanied by increases in distinct immune cell populations such as T lymphocytes and regulatory T cells in mice of either genotype. Increases in T lymphocytes, however, were less pronounced in large intestines of Nod2^−/− mice at day 7 p.i. when compared to WT mice, whereas colonic numbers of B lymphocytes were elevated in WT controls only upon C. jejuni infection. At day 7 p.i., colonic pro-inflammatory mediators including nitric oxide, TNF, IFN-γ and IL-22 increased more distinctly in Nod2^−/− as compared to WT mice, whereas C. jejuni induced IL-23p19 and IL-18 levels were lower in the large intestines of the former. Converse to the colon, however, ileal concentrations of nitric oxide, TNF, IFN-γ, IL-6 and IL-10 were lower in Nod2^−/− as compared to WT mice at day 7 p.i. Even though MUC2 was down-regulated in C. jejuni infected Nod2^−/− mice, this did not result in increased pathogenic translocation from the intestinal tract to extra-intestinal compartments.

Conclusion

In secondary abiotic mice, Nod2 signaling is involved in the orchestrated host immune responses upon C. jejuni infection, but does not control pathogen loads in the gastrointestinal tract.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0182-0) contains supplementary material, which is available to authorized users.

Amelioration of intestinal and systemic sequelae of murine Campylobacter jejuni infection by probiotic VSL#3 treatment

Background

The incidence of human Campylobacter jejuni infections is progressively increasing worldwide. Probiotic compounds might open up valuable tools to decrease pathogen burden and subsequent pro-inflammatory immune responses, but in vivo data are scarce.

Methods and results

Secondary abiotic mice generated by broad-spectrum antibiotic treatment were perorally challenged with the commercial probiotic compound VSL#3 consisting of Streptococcus thermophilus, Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus delbrueckii ssp. bulgaricus) either 5 days before (i.e. prophylactic regimen) or after (i.e. therapeutic regimen) peroral C. jejuni strain 81–176 infection, and analyzed 3 weeks following the initial bacterial re-association. Upon challenge, mice were colonized with the probiotic bacteria and/or C. jejuni at comparable intestinal loads, but co-colonization did not result in reduction of the pathogen burden. Remarkably, prophylactic as well as therapeutic VSL#3 treatment of C. jejuni infected mice ameliorated intestinal apoptosis and pro-inflammatory immune responses as indicated by lower numbers of innate and adaptive immune cell populations in the murine colon upon probiotic prophylaxis or treatment and reduced colonic concentrations of pro-inflammatory mediators including IL-6 and MCP-1. Importantly, concentrations of anti-inflammatory mediators such as IL-10 were significantly elevated in the colon of probiotics treated mice as compared to untreated controls. Strikingly, prophylactic VSL#3 treatment attenuated C. jejuni induced systemic pro-inflammatory responses as indicated by less TNF and IL-12p70 secretion in the spleen of VSL#3 pre-treated as compared to non-treated mice.

Conclusion

Administration of probiotic formulations such as VSL#3 might open up valuable strategies for prophylaxis and/or treatment of C. jejuni induced intestinal and systemic sequelae in vivo by the suppression of pro-inflammatory and induction of anti-inflammatory responses.

Exploring functional membrane microdomains in bacteria: an overview

Recent studies show that internal organization of bacterial cells is more complex than previously appreciated. A clear example of this is the assembly of the nanoscale membrane platforms termed functional membrane microdomains. The lipid composition of these regions differs from that of the surrounding membrane; these domains confine a set of proteins involved in specific cellular processes such as protease secretion and signal transduction. It is currently thought that functional membrane microdomains act as oligomerization platforms and promote efficient oligomerization of interacting protein partners in bacterial membranes. In this review, we highlight the most noteworthy achievements, challenges and controversies of this emerging research field over the past five years.

Microbiota Composition and Immune Responses During Campylobacter Jejuni Infection in Conventionally Colonized IL-10-/- Mice Lacking Nucleotide Oligomerization Domain 2

Host immune responses are pivotal for combating enteropathogenic infections. We here assessed the impact of the innate receptor nucleotide oligomerization domain protein 2 (NOD2) in murine Campylobacter jejuni-infection. Conventionally colonized IL-10^–/– mice lacking NOD2 and IL-10^–/– controls were perorally challenged with C. jejuni strain 81-176 and displayed comparable pathogenic colonization of intestines until day 14 postinfection (p.i.). Whereas overall intestinal microbiota compositions were comparable in naive mice, NOD2^–/– IL-10^–/– mice exhibited less fecal bifidobacteria and lactobacilli than IL-10^–/– counterparts after infection. Interestingly, NOD2^–/– IL-10^–/– mice were clinically more compromised during the early phase of infection, whereas, conversely, IL-10^–/– animals exhibited more frequently bloody feces lateron. While colonic apoptotic cell and T lymphocyte numbers were comparable in either C. jejuni-infected mice, B lymphocytes were lower in the colon of infected NOD2^–/– IL-10^–/– mice versus controls. At day 14 p.i., colonic TNF and IL-23p19 mRNA levels were upregulated in NOD2^–/– IL-10^–/– mice only. Translocation rates of intestinal commensals to mesenteric lymphnodes and extra-intestinal compartments including liver and kidney were comparable, whereas viable bacteria were more frequently detected in spleens derived from IL-10^–/– as compared to NOD2^–/– IL-10^–/– mice. In conclusion, NOD2 is involved during C. jejuni infection in conventionally colonized IL-10^–/– mice in a time-dependent manner.

The Human Milk Oligosaccharide 2'-Fucosyllactose Quenches Campylobacter jejuni-Induced Inflammation in Human Epithelial Cells HEp-2 and HT-29 and in Mouse Intestinal Mucosa

BACKGROUND

Campylobacter jejuni causes diarrhea worldwide; young children are most susceptible. Binding of virulent C. jejuni to the intestinal mucosa is inhibited ex vivo by α_1,2-fucosylated carbohydrate moieties, including human milk oligosaccharides (HMOSs).

OBJECTIVE

The simplest α_1,2-fucosylated HMOS structure, 2'-fucosyllactose (2'-FL), can be predominant at ≤5 g/L milk. Although 2'-FL inhibits C. jejuni binding ex vivo and in vivo, the effects of 2'FL on the cell invasion central to C. jejuni pathogenesis have not been tested. Clinical isolates of C. jejuni infect humans, birds, and ferrets, limiting studies on its mammalian pathobiology.

METHODS

Human epithelial cells HEp-2 and HT-29 infected with the virulent C. jejuni strain 81-176 human isolate were treated with 5 g 2'-FL/L, and the degree of infection and inflammatory response was measured. Four-week-old male wild-type C57BL/6 mice were fed antibiotics to reduce their intestinal microbiota and were inoculated with C. jejuni strain 81-176. The sensitivity of the resulting acute transient enteric infection and immune response to inhibition by 2'-FL ingestion was tested.

RESULTS

In HEp-2 and HT-29 cells, 2'-FL attenuated 80% of C. jejuni invasion (P < 0.05) and suppressed the release of mucosal proinflammatory signals of interleukin (IL) 8 by 60-70%, IL-1β by 80-90%, and the neutrophil chemoattractant macrophage inflammatory protein 2 (MIP-2) by 50% (P < 0.05). Ingestion of 2'-FL by mice reduced C. jejuni colonization by 80%, weight loss by 5%, histologic features of intestinal inflammation by 50-70%, and induction of inflammatory signaling molecules of the acute-phase mucosal immune response by 50-60% (P < 0.05). This acute model did not induce IL-17 (adaptive T cell response), a chronic response.

CONCLUSIONS

In human cells in vitro (HEp-2, HT-29) and in a mouse infection model that recapitulated key pathologic features of C. jejuni clinical disease, 2'-FL inhibited pathogenesis and its sequelae. These data strongly support the hypothesis that 2'-FL represents a new class of oral agent for prevention, and potentially for treatment, of specific enteric infectious diseases.

Functional Membrane Microdomains Organize Signaling Networks in Bacteria

Membrane organization is usually associated with the correct function of a number of cellular processes in eukaryotic cells as diverse as signal transduction, protein sorting, membrane trafficking, or pathogen invasion. It has been recently discovered that bacterial membranes are able to compartmentalize their signal transduction pathways in functional membrane microdomains (FMMs). In this review article, we discuss the biological significance of the existence of FMMs in bacteria and comment on possible beneficial roles that FMMs play on the harbored signal transduction cascades. Moreover, four different membrane-associated signal transduction cascades whose functions are linked to the integrity of FMMs are introduced, and the specific role that FMMs play in stabilizing and promoting interactions of their signaling components is discussed. Altogether, FMMs seem to play a relevant role in promoting more efficient activation of signal transduction cascades in bacterial cells and show that bacteria are more sophisticated organisms than previously appreciated.

The Immunopathogenic Potential of Arcobacter butzleri - Lessons from a Meta-Analysis of Murine Infection Studies

Background

Only limited information is available about the immunopathogenic properties of Arcobacter infection in vivo. Therefore, we performed a meta-analysis of published data in murine infection models to compare the pathogenic potential of Arcobacter butzleri with Campylobacter jejuni and commensal Escherichia coli as pathogenic and harmless reference bacteria, respectively.

Methodology / Principal Findings

Gnotobiotic IL-10^-/- mice generated by broad-spectrum antibiotic compounds were perorally infected with A. butzleri (strains CCUG 30485 or C1), C. jejuni (strain 81-176) or a commensal intestinal E. coli strain. Either strain stably colonized the murine intestines upon infection. At day 6 postinfection (p.i.), C. jejuni infected mice only displayed severe clinical sequelae such as wasting bloody diarrhea. Gross disease was accompanied by increased numbers of colonic apoptotic cells and distinct immune cell populations including macrophages and monocytes, T and B cells as well as regulatory T cells upon pathogenic infection. Whereas A. butzleri and E. coli infected mice were clinically unaffected, respective colonic immune cell numbers increased in the former, but not in the latter, and more distinctly upon A. butzleri strain CCUG 30485 as compared to C1 strain infection. Both, A. butzleri and C. jejuni induced increased secretion of pro-inflammatory cytokines such as IFN-γ, TNF, IL-6 and MCP-1 in large, but also small intestines. Remarkably, even though viable bacteria did not translocate from the intestines to extra-intestinal compartments, systemic immune responses were induced in C. jejuni, but also A. butzleri infected mice as indicated by increased respective pro-inflammatory cytokine concentrations in serum samples at day 6 p.i.

Conclusion / Significance

A. butzleri induce less distinct pro-inflammatory sequelae as compared to C. jejuni, but more pronounced local and systemic immune responses than commensal E. coli in a strain-dependent manner. Hence, data point towards that A. butzleri is more than a commensal in vertebrate hosts.

Interleukin-18 Mediates Immune Responses to Campylobacter jejuni Infection in Gnotobiotic Mice

BACKGROUND

Human Campylobacter jejuni infections are progressively rising worldwide. Information about the molecular mechanisms underlying campylobacteriosis, however, are limited. In the present study we investigated whether cytokines such as IL-23, IL-22 and IL-18, which share pivotal functions in host immunity, were involved in mediating intestinal and systemic immunopathological responses upon C. jejuni infection.

METHODOLOGY/PRINCIPAL FINDINGS

To assure stable infection, gnotobiotic (i.e. secondary abiotic) IL-23p19-/-, IL-22-/- and IL-18-/- mice were generated by broad-spectrum antibiotic treatment. Following peroral C. jejuni strain 81-176 infection, mice of all genotypes harbored comparably high pathogenic loads in their intestines. As compared to wildtype controls, however, IL-18-/- mice displayed less distinct C. jejuni induced sequelae as indicated by less pronounced large intestinal shrinkage and lower numbers of apoptotic cells in the colonic epithelial layer at day 8 postinfection (p.i.). Furthermore, lower colonic numbers of adaptive immune cells including regulatory T cells and B lymphocytes were accompanied by less distinct secretion of pro-inflammatory cytokines such as TNF and IFN-γ and lower IL-17A mRNA expression levels in colonic ex vivo biopsies of infected IL-18-/- as compared to wildtype mice. Upon C. jejuni infection, colonic IL-23p19 expression was up-regulated in IL-18-/- mice only, whereas IL-22 mRNA levels were lower in uninfected and infected IL-23p19-/- as well as infected IL-18-/- as compared to respective wildtype control mice. Remarkably, not only intestinal, but also systemic infection-induced immune responses were less pronounced in IL-18-/- mice as indicated by lower TNF, IFN-γ and IL-6 serum levels as compared to wildtype mice.

CONCLUSION/SIGNIFICANCE

We here show for the first time that IL-18 is essentially involved in mediating C. jejuni infection in the gnotobiotic mouse model. Future studies need to further unravel the underlying regulatory mechanisms orchestrating pathogen-host interaction.

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.

Intestinal Expression of Genes Encoding Inflammatory Mediators and Gelatinases During Arcobacter Butzleri Infection of Gnotobiotic Il-10 Deficient Mice

We have previously shown that Arcobacter butzleri induces intestinal, extra-intestinal, and systemic immune responses in perorally infected gnotobiotic IL-10(-/-) mice in a strain-dependent fashion. Here, we present a comprehensive survey of small and large intestinal expression profiles of inflammatory and regulatory mediators as well as of the matrix-degrading gelatinases MMP-2 and MMP-9 following murine A. butzleri infection. Gnotobiotic IL-10(-/-) mice were infected with A. butzleri strains CCUG 30485 or C1 of human and chicken origin, respectively. At day 6 following A. butzleri infection, mucin-2 mRNA, an integral part of the intestinal mucus layer, was downregulated in the colon, whereas TNF and IL-23p19 mRNA were upregulated in the ileum. Furthermore, IFN-γ, IL-17A, IL-1β, and IL-22 mRNA were upregulated in both colonic and ileal ex vivo biopsies at day 6 post strain CCUG 30485 infection. These changes were accompanied by downregulated colonic MMP-9 levels, whereas both MMP-2 and MMP-9 mRNA were upregulated in the ileum. In conclusion, these data indicate that A. butzleri infection induces changes in the expression of genes involved in pro-inflammatory and regulatory immune responses as well as in tissue degradation.

Toll-Like Receptor-4 is Essential for Arcobacter Butzleri-Induced Colonic and Systemic Immune Responses in Gnotobiotic IL-10(-/-) Mice

Arcobacter butzleri causes sporadic cases of gastroenteritis, but the underlying immunopathological mechanisms of infection are unknown. We have recently demonstrated that A. butzleri-infected gnotobiotic IL-10^–/– mice were clinically unaffected but exhibited intestinal and systemic inflammatory immune responses. For the first time, we here investigated the role of Toll-like receptor (TLR)-4, the main receptor for lipopolysaccharide and lipooligosaccharide of Gram-negative bacteria, in murine arcobacteriosis. Gnotobiotic TLR-4/IL-10-double deficient (TLR-4^–/– IL-10^–/–) and IL-10^–/– control mice generated by broad-spectrum antibiotics were perorally infected with A. butzleri. Until day 16 postinfection, mice of either genotype were stably colonized with the pathogen, but fecal bacterial loads were approximately 0.5–2.0 log lower in TLR-4^–/– IL-10^–/– as compared to IL-10^–/– mice. A. butzleri-infected TLR-4^–/– IL-10^–/– mice displayed less pronounced colonic apoptosis accompanied by lower numbers of macrophages and monocytes, T lymphocytes, regulatory T-cells, and B lymphocytes within the colonic mucosa and lamina propria as compared to IL-10^–/– mice. Furthermore, colonic concentrations of nitric oxide, TNF, IL-6, MCP-1, and, remarkably, IFN-γ and IL-12p70 serum levels were lower in A. butzleri-infected TLR-4^–/– IL-10^–/– versus IL-10^–/– mice. In conclusion, TLR-4 is involved in mediating murine A. butzleri infection. Further studies are needed to investigate the molecular mechanisms underlying Arcobacter–host interactions in more detail.

Toll-Like Receptor-4 Dependent Small Intestinal Immune Responses Following Murine Arcobacter Butzleri Infection

Sporadic cases of gastroenteritis have been attributed to Arcobacter butzleri infection, but information about the underlying immunopathological mechanisms is scarce. We have recently shown that experimental A. butzleri infection induces intestinal, extraintestinal and systemic immune responses in gnotobiotic IL-10(-/-) mice. The aim of the present study was to investigate the immunopathological role of Toll-like Receptor-4, the receptor for lipopolysaccharide and lipooligosaccharide of Gram-negative bacteria, during murine A. butzleri infection. To address this, gnotobiotic IL-10(-/-) mice lacking TLR-4 were generated by broad-spectrum antibiotic treatment and perorally infected with two different A. butzleri strains isolated from a patient (CCUG 30485) or fresh chicken meat (C1), respectively. Bacteria of either strain stably colonized the ilea of mice irrespective of their genotype at days 6 and 16 postinfection. As compared to IL-10(-/-) control animals, TLR-4(-/-) IL-10(-/-) mice were protected from A. butzleri-induced ileal apoptosis, from ileal influx of adaptive immune cells including T lymphocytes, regulatory T-cells and B lymphocytes, and from increased ileal IFN-γ secretion. Given that TLR-4-signaling is essential for A. butzleri-induced intestinal inflammation, we conclude that bacterial lipooligosaccharide or lipopolysaccharide compounds aggravate intestinal inflammation and may thus represent major virulence factors of Arcobacter. Future studies need to further unravel the molecular mechanisms of TLR-4-mediated A. butzleri-host interactions.

Campylobacter jejuni outer membrane vesicle-associated proteolytic activity promotes bacterial invasion by mediating cleavage of intestinal epithelial cell E-cadherin and occludin

Outer membrane vesicles (OMVs) play an important role in the pathogenicity of Gram-negative bacteria. Campylobacter jejuni produces OMVs that trigger IL-8, IL-6, hBD-3 and TNF-α responses from T84 intestinal epithelial cells and are cytotoxic to Caco-2 IECs and Galleria mellonella larvae. Proteomic analysis of 11168H OMVs identified the presence of three proteases, HtrA, Cj0511 and Cj1365c. In this study, 11168H OMVs were shown to possess proteolytic activity that was reduced by pretreatment with specific serine protease inhibitors. OMVs isolated from 11168H htrA, Cj0511 or Cj1365c mutants possess significantly reduced proteolytic activity. 11168H OMVs are able to cleave both E-cadherin and occludin, but this cleavage is reduced with OMVs pretreated with serine protease inhibitors and also with OMVs isolated from htrA or Cj1365c mutants. Co-incubation of T84 monolayers with 11168H OMVs results in a visible reduction in both E-cadherin and occludin. The addition of 11168H OMVs to the co-culture of live 11168H bacteria with T84 cells results in enhanced levels of bacterial adhesion and invasion in a time-dependent and dose-dependent manner. Further investigation of the cleavage of host cell structural proteins by C. jejuni OMVs should enhance our understanding of the interactions of this important pathogen with intestinal epithelial cells.

The Role of Gelatinases in Campylobacter Jejuni Infection of Gnotobiotic Mice

Matrix metalloproteinases (MMP)-2 and -9 (also referred to gelatinases-A and -B, respectively) are upregulated in the inflamed gut of mice and men. We recently demonstrated that synthetic gelatinase blockage reduced large intestinal pro-inflammatory immune responses and apoptosis following murine Campylobacter (C.) jejuni infection. In order to address which gelatinase mediates C. jejuni-induced immune responses, gnotobiotic MMP-2(-/-), MMP-9(-/-), and wildtype (WT) mice were generated by broadspectrum antibiotic treatment and perorally infected with C. jejuni strain 81-176. The pathogen stably colonized the murine intestinal tract irrespective of the genotype but did not translocate to extra-intestinal compartments. At days 8 and 14 postinfection (p.i.), less pronounced colonic histopathological changes were observed in infected MMP-2(-/-) mice, less distinct epithelial apoptosis, but more epithelial proliferation in both MMP-2(-/-) and MMP-9(-/-) mice, as compared to WT controls. Reduced immune responses in gelatinase-deficient mice were characterized by lower numbers of effector as well as innate and adaptive immune cells within the colonic mucosa and lamina propria. The expression of IL-22, IL-18, IL-17A, and IL-1β mRNA was higher in the colon of MMP-2(-/-) as compared to WT mice. In conclusion, both MMP-2 and MMP-9 are differentially involved in mediating C. jejuni-induced intestinal immunopathology.

Survey of small intestinal and systemic immune responses following murine Arcobacter butzleri infection

BACKGROUND

Arcobacter (A.) butzleri has been described as causative agent for sporadic cases of human gastroenteritis with abdominal pain and acute or prolonged watery diarrhea. In vitro studies revealed distinct adhesive, invasive and cytotoxic properties of A. butzleri. Information about the underlying immunopathological mechanisms of infection in vivo, however, are scarce. The aim of this study was to investigate the immunopathological properties of two different A. butzleri strains in a well-established murine infection model.

RESULTS

Gnotobiotic IL-10(-/-) mice, in which the intestinal microbiota was depleted by broad-spectrum antibiotic treatment, were perorally infected with two different A. butzleri strains isolated from a diseased patient (CCUG 30485) or fresh chicken meat (C1), respectively. Eventhough bacteria of either strain could stably colonize the intestinal tract at day 6 and day 16 postinfection (p.i.), mice did not exert infection induced symptoms such as diarrhea or wasting. In small intestines of infected mice, however, increased numbers of apoptotic cells could be detected at day 16, but not day 6 following infection with either strain. A strain-dependent influx of distinct immune cell populations such as T and B cells as well as of regulatory T cells could be observed upon A. butzleri infection which was accompanied by increased small intestinal concentrations of pro-inflammatory cytokines such as TNF, IFN-γ, MCP-1 and IL-6. Remarkably, inflammatory responses following A. butzleri infection were not restricted to the intestinal tract, given that the CCUG 30485 strain induced systemic immune responses as indicated by increased IFN-γ concentrations in spleens at day 6, but not day 16 following infection.

CONCLUSION

Upon peroral infection A. butzleri stably colonized the intestinal tract of gnotobiotic IL-10(-/-) mice. The dynamics of distinct local and systemic inflammatory responses could be observed in a strain-dependent fashion pointing towards an immunopathogenic potential of A. butzleri in vivo. These results indicate that gnotobiotic IL-10(-/-) mice are well suited to further investigate the molecular mechanisms underlying arcobacteriosis in vivo.

Arcobacter butzleri Induce Colonic, Extra-Intestinal and Systemic Inflammatory Responses in Gnotobiotic IL-10 Deficient Mice in a Strain-Dependent Manner

Background

The immunopathological impact of human Arcobacter (A.) infections is under current debate. Episodes of gastroenteritis with abdominal pain and acute or prolonged watery diarrhea were reported for A. butzleri infected patients. Whereas adhesive, invasive and cytotoxic capacities have been described for A. butzleri in vitro, only limited information is available about the immunopathogenic potential and mechanisms of infection in vivo.

Methodology/Principal Findings

Gnotobiotic IL-10^-/- mice were generated by broad-spectrum antibiotic treatment and perorally infected with the A. butzleri strains CCUG 30485 and C1 shown to be invasive in cell culture assays. Bacterial colonization capacities, clinical conditions, intestinal, extra-intestinal and systemic immune responses were monitored at day six and 16 postinfection (p.i.). Despite stable intestinal A. butzleri colonization at high loads, gnotobiotic IL-10^-/- mice were virtually unaffected and did not display any overt symptoms at either time point. Notably, A. butzleri infection induced apoptosis of colonic epithelial cells which was paralleled by increased abundance of proliferating cells. Furthermore A. butzleri infection caused a significant increase of distinct immune cell populations such as T and B cells, regulatory T cells, macrophages and monocytes in the colon which was accompanied by elevated colonic TNF, IFN-γ, nitric oxide (NO), IL-6, IL-12p70 and MCP-1 concentrations. Strikingly, A. butzleri induced extra-intestinal and systemic immune responses as indicated by higher NO concentrations in kidney and increased TNF, IFN-γ, IL-12p70 and IL-6 levels in serum samples of infected as compared to naive mice. Overall, inflammatory responses could be observed earlier in the course of infection by the CCUG 30485 as compared to the C1 strain.

Conclusion/Significance

Peroral A. butzleri infection induced not only intestinal but also extra-intestinal and systemic immune responses in gnotobiotic IL-10^-/- mice in a strain-dependent manner. These findings point towards an immunopathogenic potential of A. butzleri in vertebrate hosts.

Matrix Metalloproteinase-2 Mediates Intestinal Immunopathogenesis in Campylobacter Jejuni-Infected Infant Mice

Increased levels of the matrix metalloproteinases (MMPs)-2 and -9 (also referred to gelatinase-A and -B, respectively) can be detected in the inflamed gut. We have recently shown that synthetic gelatinase blockage reduces colonic apoptosis and pro-inflammatory immune responses following murine Campylobacter (C.) jejuni infection. In order to dissect whether MMP-2 and/or MMP-9 is involved in mediating C. jejuni-induced immune responses, infant MMP-2(-/-), MMP-9(-/-), and wildtype (WT) mice were perorally infected with the C. jejuni strain B2 immediately after weaning. Whereas, at day 2 postinfection (p.i.), fecal C. jejuni B2 loads were comparable in mice of either genotype, mice expelled the pathogen from the intestinal tract until day 4 p.i. Six days p.i., colonic MMP-2 but not MMP-9 mRNA was upregulated in WT mice. Remarkably, infected MMP-2(-/-) mice exhibited less frequent abundance of blood in feces, less distinct colonic histopathology and apoptosis, lower numbers of effector as well as innate and adaptive immune cells within the colonic mucosa, and higher colonic IL-22 mRNA levels as compared to infected WT mice. In conclusion, these results point towards an important role of MMP-2 in mediating C. jejuni-induced intestinal immunopathogenesis.

Selective gelatinase inhibition reduces apoptosis and pro-inflammatory immune cell responses in Campylobacter jejuni-infected gnotobiotic IL-10 deficient mice

Increased levels of the matrix metalloproteinases-2 and -9 (also referred to gelatinase-A and -B, respectively) can be detected in intestinal inflammation. We have recently shown that selective gelatinase blockage by the synthetic compound RO28-2653 ameliorates acute murine ileitis and colitis. We here investigated whether RO28-2653 exerts anti-inflammatory effects in acute Campylobacter jejuni-induced enterocolitis of gnotobiotic IL-10(-/-) mice generated following antibiotic treatment. Mice were perorally infected with C. jejuni (day 0) and either treated with RO28-2653 (75 mg/kg body weight/day) or placebo from day 1 until day 6 post infection (p.i.) by gavage. Irrespective of the treatment, infected mice displayed comparable pathogen loads within the gastrointestinal tract. Following RO28-2653 administration, however, infected mice exhibited less severe symptoms such as bloody diarrhea as compared to placebo controls. Furthermore, less distinct apoptosis but higher numbers of proliferating cells could be detected in the colon of RO28-2653-treated as compared to placebo-treated mice at day 7 p.i. Remarkably, gelatinase blockage resulted in lower numbers of T- and B-lymphocytes as well as macrophages and monocytes in the colonic mucosa of C. jejuni-infected gnotobiotic IL-10(-/-) mice. Taken together, synthetic gelatinase inhibition exerts anti-inflammatory effects in experimental campylobacteriosis.

The role of serine protease HtrA in acute ulcerative enterocolitis and extra-intestinal immune responses during Campylobacter jejuni infection of gnotobiotic IL-10 deficient mice

Campylobacter jejuni infections have a high prevalence worldwide and represent a significant socioeconomic burden. C. jejuni can cross the intestinal epithelial barrier as visualized in biopsies derived from human patients and animal models, however, the underlying molecular mechanisms and associated immunopathology are still not well understood. We have recently shown that the secreted serine protease HtrA (high temperature requirement A) plays a key role in C. jejuni cellular invasion and transmigration across polarized epithelial cells in vitro. In the present in vivo study we investigated the role of HtrA during C. jejuni infection of mice. We used the gnotobiotic IL-10^−/− mouse model to study campylobacteriosis following peroral infection with the C. jejuni wild-type (WT) strain NCTC11168 and the isogenic, non-polar NCTC11168ΔhtrA deletion mutant. Six days post infection (p.i.) with either strain mice harbored comparable intestinal C. jejuni loads, whereas ulcerative enterocolitis was less pronounced in mice infected with the ΔhtrA mutant strain. Moreover, ΔhtrA mutant infected mice displayed lower apoptotic cell numbers in the large intestinal mucosa, less colonic accumulation of neutrophils, macrophages and monocytes, lower large intestinal nitric oxide, IFN-γ, and IL-6 as well as lower TNF-α and IL-6 serum concentrations as compared to WT strain infected mice at day 6 p.i. Notably, immunopathological responses were not restricted to the intestinal tract given that liver and kidneys exhibited mild histopathological changes 6 days p.i. with either C. jejuni strain. We also found that hepatic and renal nitric oxide levels or renal TNF-α concentrations were lower in the ΔhtrA mutant as compared to WT strain infected mice. In conclusion, we show here that the C. jejuni HtrA protein plays a pivotal role in inducing host cell apoptosis and immunopathology during murine campylobacteriosis in the gut in vivo.