Insights into Campylobacter jejuni colonization of the mammalian intestinal tract using a novel mouse model of infection

In Vitro Models for Investigating Intestinal Host-Pathogen Interactions

Infectious diseases are increasingly recognized as a major threat worldwide due to the rise of antimicrobial resistance and the emergence of novel pathogens. In vitro models that can adequately mimic in vivo gastrointestinal physiology are in high demand to elucidate mechanisms behind pathogen infectivity, and to aid the design of effective preventive and therapeutic interventions. There exists a trade-off between simple and high throughput models and those that are more complex and physiologically relevant. The complexity of the model used shall be guided by the biological question to be addressed. This review provides an overview of the structure and function of the intestine and the models that are developed to emulate this. Conventional models are discussed in addition to emerging models which employ engineering principles to equip them with necessary advanced monitoring capabilities for intestinal host-pathogen interrogation. Limitations of current models and future perspectives on the field are presented.

Whole Genome Sequences, De Novo Assembly, and Annotation of Antibiotic Resistant Campylobacter jejuni Strains S27, S33, and S36 Newly Isolated from Chicken Meat

Campylobacter is a leading bacterial cause of gastrointestinal infections in humans and has imposed substantial medical and public health burdens worldwide. Among a total of 39 species in the Campylobacter genus, C. jejuni is the most important species responsible for approx. 90% of human Campylobacter illness. Most cases of the infection were acquired by ingesting undercooked poultry meat due to the high prevalence of Campylobacter in the products. Here, we reported the dataset of raw sequences, de novo assembled and annotated genomes of C. jejuni strains S27, S33, and S36 recently isolated from retail chicken by using PacBio highly accurate long-read sequencing technology combined with bioinformatics tools. Our data revealed several virulence and antibiotic resistance genes in each of the chromosomes, a type IV secretion system in the plasmid (pCjS33) of C. jejuni S33, and a type VI secretion system and a phage in the plasmid (pCjS36) of C. jejuni S36. This study not only provides new sequence data but also extends the knowledge pertaining to the genomic and functional aspects of this important foodborne pathogen, including the genetic determinants of virulence and antibiotic resistance.

Animal and In Vitro Models as Powerful Tools to Decipher the Effects of Enteric Pathogens on the Human Gut Microbiota

Examining the interplay between intestinal pathogens and the gut microbiota is crucial to fully comprehend the pathogenic role of enteropathogens and their broader impact on human health. Valid alternatives to human studies have been introduced in laboratory practice to evaluate the effects of infectious agents on the gut microbiota, thereby exploring their translational implications in intestinal functionality and overall health. Different animal species are currently used as valuable models for intestinal infections. In addition, considering the recent advances in bioengineering, futuristic in vitro models resembling the intestinal environment are also available for this purpose. In this review, the impact of the main human enteropathogens (i.e., Clostridioides difficile, Campylobacter jejuni, diarrheagenic Escherichia coli, non-typhoidal Salmonella enterica, Shigella flexneri and Shigella sonnei, Vibrio cholerae, and Bacillus cereus) on intestinal microbial communities is summarized, with specific emphasis on results derived from investigations employing animal and in vitro models.

Campylobacter jejuni uses energy taxis and a dehydrogenase enzyme for l-fucose chemotaxis

IMPORTANCE

In this study, we identify a separate role for the Campylobacter jejuni l-fucose dehydrogenase in l-fucose chemotaxis and demonstrate that this mechanism is not only limited to C. jejuni but is also present in Burkholderia multivorans. We now hypothesize that l-fucose energy taxis may contribute to the reduction of l-fucose-metabolizing strains of C. jejuni from the gastrointestinal tract of breastfed infants, selecting for isolates with increased colonization potential.

Combination of organic acids benzoate, butyrate, caprylate, and sorbate provides a novel antibiotics-independent treatment option in the combat of acute campylobacteriosis

Introduction

The food-borne Gram-negative bacterial pathogen Campylobacter jejuni may cause the acute enterocolitis syndrome campylobacteriosis in infected humans. Given that human C. jejuni infections are rising globally which hold also true for resistance rates against antibiotic compounds such as macrolides and fluoroquinolones frequently prescribed for the treatment of severe infectious enteritis, novel antibiotics-independent therapeutic strategies are needed. Distinct organic acids are well known for their health-beneficial including anti-microbial and immunomodulatory properties. In our present study, we investigated potential pathogen-lowering and anti-inflammatory effects of benzoic acid, butyric acid, caprylic acid, and sorbic acid either alone or in combination during acute murine campylobacteriosis.

Methods

Therefore, secondary abiotic IL-10–/– mice were perorally infected with C. jejuni strain 81–176 and subjected to a 4-day-course of respective organic acid treatment.

Results and discussion

On day 6 post-infection, mice from the combination cohort displayed slightly lower pathogen loads in the duodenum, but neither in the stomach, ileum nor large intestine. Remarkably, the clinical outcome of C. jejuni induced acute enterocolitis was significantly improved after combined organic acid treatment when compared to the placebo control group. In support, the combinatory organic acid treatment dampened both, macroscopic and microscopic inflammatory sequelae of C. jejuni infection as indicated by less colonic shrinkage and less pronounced histopathological including apoptotic epithelial cell changes in the colon on day 6 post-infection. Furthermore, mice from the combination as compared to placebo cohort exhibited lower numbers of innate and adaptive immune cells such as neutrophilic granulocytes, macrophages, monocytes, and T lymphocytes in their colonic mucosa and lamina propria, respectively, which also held true for pro-inflammatory cytokine secretion in the large intestines and mesenteric lymph nodes. Notably, the anti-inflammatory effects were not restricted to the intestinal tract, but could also be observed systemically given pro-inflammatory mediator concentrations in C. jejuni infected mice from the combination organic acid treatment that were comparable to basal values. In conclusion, our in vivo study provides first evidence that an oral application of distinct organic acids in combination exhibits pronounced anti-inflammatory effects and hence, constitutes a promising novel antibiotics-independent therapeutic strategy in the combat of acute campylobacteriosis.

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.

Effects of Sublethally Injured Campylobacter jejuni in Mice

Globally, Campylobacter spp. are the most common food-associated bacterial cause of human gastrointestinal disease. Campylobacteriosis is primarily associated with the consumption of contaminated chicken meat. Chemical decontamination of chicken carcasses during processing is one of the most effective interventions to mitigate Campylobacter contamination. Following exposure to sanitizers, however, sublethally injured populations of bacteria may persist. The risk that sublethally injured Campylobacter pose for public health is unknown. Furthermore, the virulence potential of sublethally injured Campylobacter jejuni during prolonged storage in relation to host pathogenesis and the host immune response has not been well established. Therefore, we evaluated the effects of sublethally injured C. jejuni on the host, after storage in chicken meat juice. C57BL/6 mice were infected with two C. jejuni chicken meat isolates or the ATCC 33291 strain that had been stored in the chicken meat juice, after exposure to chlorine or acidified sodium chlorite (ASC). Although chlorine exposure was unable to reduce intestinal colonization by C. jejuni, exposure to ASC significantly reduced the intestinal colonization and tissue translocation in mice. The expression of pro- and anti-inflammatory cytokine genes for interleukin-6 (IL-6), IL23a, and IL-10, Toll-like receptor 2 (TLR2) and TLR4 genes, and host stress response genes (CRP, MBL1, and NF-κB1) were significantly reduced following the exposure to ASC. Our results demonstrated that sublethally injured C. jejuni has reduced virulence potential and colonization in mice. The data contribute toward clarification of the importance of chemical decontamination during processing to minimize human campylobacteriosis.

IMPORTANCECampylobacter is the most common cause of bacterial gastrointestinal disease, and consumption of contaminated poultry is frequently identified as the source of bacteria. The survivability and virulence potential of sublethally injured Campylobacter following exposure to chemicals which are commonly used to eliminate Campylobacter during the poultry meat processing are of concern to the food industry, government health officials, and consumers. Here, we demonstrate that sublethally injured Campylobacter jejuni has reduced bacterial virulence and colonization potential in mice.

Bioengineering of LAB vector expressing Haemolysin co-regulated protein (Hcp): a strategic approach to control gut colonization of Campylobacter jejuni in a murine model

Background

Campylobacter jejuni (C. jejuni) is accountable for more than 400 million cases of gastroenteritis each year and is listed as a high-priority gut pathogen by the World Health Organization (WHO). Although the acute infection of C. jejuni (campylobacteriosis) is commonly treated with macrolides and fluoroquinolones, the emergence of antibiotic resistance among C. jejuni warrants the need for an alternative approach to control campylobacteriosis in humans. To this end, vaccines remain a safe, effective, and widely accepted strategy for controlling emerging and re-emerging infectious diseases. In search of a suitable vaccine against campylobacteriosis, recently, we demonstrated the potential of recombinant Haemolysin co-regulated protein (Hcp) of C. jejuni Type VI secretion system (T6SS) in imparting significant immune-protection against cecal colonization of C. jejuni; however, in the avian model. Since clinical features of human campylobacteriosis are more complicated than the avians, we explored the potential of Hcp as a T6SS targeted vaccine in a murine model as a more reliable and reproducible experimental host to study vaccine-induced immune-protection against C. jejuni. Because C. jejuni primarily utilizes the mucosal route for host pathogenesis, we analyzed the immunogenicity of a mucosally deliverable bioengineered Lactic acid bacteria (LAB), Lactococcus lactis (L. lactis), expressing Hcp. Considering the role of Hcp in both structural (membrane-bound) and functional (effector protein) exhibition of C. jejuni T6SS, a head-to-head comparison of two different forms of recombinant LAB vectors (cell wall anchored and secreted form of Hcp) were tested and assessed for the immune phenotypes of each modality in BALB/c mice.

Results

We show that regardless of the Hcp protein localization, mucosal delivery of bioengineered LAB vector expressing Hcp induced high-level production of antigen-specific neutralizing antibody (sIgA) in the gut with the potential to reduce the cecal load of C. jejuni in mice.

Conclusion

Together with the non-commensal nature of L. lactis, short gut transit time in humans, and the ability to express the heterologous protein in the gut, the present study highlights the benefits of bioengineered LAB vectors based mucosal vaccine modality against C. jejuni without the risk of immunotolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13099-021-00444-2.

The Host Cellular Immune Response to Infection by Campylobacter Spp. and Its Role in Disease

Campylobacter spp. are the leading cause of bacterium-derived gastroenteritis worldwide, impacting 96 million individuals annually. Unlike other bacterial pathogens of the gastrointestinal tract, Campylobacter spp. lack many of the classical virulence factors that are often associated with the ability to induce disease in humans, including an array of canonical secretion systems and toxins. Consequently, the clinical manifestations of human campylobacteriosis and its resulting gastrointestinal pathology are believed to be primarily due to the host immune response toward the bacterium. Further, while gastrointestinal infection is usually self-limiting, numerous postinfectious disorders can occur, including the development of Guillain-Barré syndrome, reactive arthritis, and irritable bowel syndrome. Because gastrointestinal disease likely results from the host immune response, the development of these postinfectious disorders may be due to dysregulation or misdirection of the same inflammatory response. As a result, it is becoming increasingly important to the Campylobacter field, and human health, that the cellular immune responses toward Campylobacter be better understood, including which immunological events are critical to the development of disease and the postinfectious disorders mentioned above. In this review, we collectively cover the cellular immune responses across susceptible hosts to Campylobacter jejuni infection, along with the tissue pathology and postinfectious disorders which may develop.

Immune-Modulatory Effects upon Oral Application of Cumin-Essential-Oil to Mice Suffering from Acute Campylobacteriosis

Human campylobacteriosis, commonly caused by Campylobacter jejuni, is a food-borne infection with rising prevalence causing significant health and socioeconomic burdens worldwide. Given the threat from emerging antimicrobial resistances, the treatment of infectious diseases with antibiotics-independent natural compounds is utmost appreciated. Since the health-beneficial effects of cumin-essential-oil (EO) have been known for centuries, its potential anti-pathogenic and immune-modulatory effects during acute experimental campylobacteriosis were addressed in the present study. Therefore, C. jejuni-challenged secondary abiotic IL-10^-/- mice were treated perorally with either cumin-EO or placebo starting on day 2 post-infection. On day 6 post-infection, cumin-EO treated mice harbored lower ileal pathogen numbers and exhibited a better clinical outcome when compared to placebo controls. Furthermore, cumin-EO treatment alleviated enteropathogen-induced apoptotic cell responses in colonic epithelia. Whereas, on day 6 post-infection, a dampened secretion of pro-inflammatory mediators, including nitric oxide and IFN-γ to basal levels, could be assessed in mesenteric lymph nodes of cumin-EO treated mice, systemic MCP-1 concentrations were elevated in placebo counterparts only. In conclusion, our preclinical intervention study provides first evidence for promising immune-modulatory effects of cumin-EO in the combat of human campylobacteriosis. Future studies should address antimicrobial and immune-modulatory effects of natural compounds as adjunct antibiotics-independent treatment option for infectious diseases.

Resveratrol Prevents Campylobacter jejuni-Induced Leaky gut by Restoring Occludin and Claudin-5 in the Paracellular Leak Pathway

Campylobacter jejuni is a bacterial human pathogen causing gastroenteritis and sequelae like irritable bowel syndrome. Epidemiologists count the human campylobacteriosis by C. jejuni as the most common foodborne zoonosis and bacterial diarrheal disease worldwide. Based on bioinformatics predictions for potential protective compounds in campylobacteriosis, the question was raised whether the plant-based polyphenol resveratrol is sufficient to attenuate intestinal epithelial damage induced by C. jejuni. We investigated this by performing experimental infection studies in an epithelial cell culture and the secondary abiotic IL-10-/- mouse model. In C. jejuni-infected human colonic HT-29/B6 cell monolayers, transepithelial electrical resistance (TER) was decreased and the paracellular marker flux of fluorescein (332 Da) increased. Concomitantly, the tight junction (TJ) proteins occludin and claudin-5 were re-distributed off the tight junction domain. This was accompanied by an increased induction of epithelial apoptosis, both changes contributing to compromised barrier function and the opening of the leak pathway induced by C. jejuni. In parallel, the recovery experiments with the application of resveratrol revealed a functional improvement of the disturbed epithelial barrier in both models in vitro and in vivo. During treatment with resveratrol, TJ localization of occludin and claudin-5 was fully restored in the paracellular domain of HT-29/B6 cells. Moreover, resveratrol decreased the rate of epithelial apoptosis. These resveratrol-induced molecular and cellular effects would therefore be expected to improve epithelial barrier function, thereby minimizing the so-called leaky gut phenomenon. In conclusion, the induction of the leak pathway by C. jejuni and the restoration of barrier function by resveratrol demonstrates its effectiveness as a potential preventive or therapeutic method of mitigating the leaky gut associated with campylobacteriosis.

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.

Induction of neutrophil extracellular traps by Campylobacter jejuni

Campylobacter jejuni is the leading cause of bacterial-derived gastroenteritis worldwide and can lead to several post-infectious inflammatory disorders. Despite the prevalence and health impacts of the bacterium, interactions between the host innate immune system and C. jejuni remain poorly understood. To expand on earlier work demonstrating that neutrophils traffic to the site of infection in an animal model of campylobacteriosis, we identified significant increases in several predominantly neutrophil-derived proteins in the faeces of C. jejuni-infected patients, including lipocalin-2, myeloperoxidase and neutrophil elastase. In addition to demonstrating that these proteins significantly inhibited C. jejuni growth, we determined they are released during formation of C. jejuni-induced neutrophil extracellular traps (NETs). Using quantitative and qualitative methods, we found that purified human neutrophils are activated by C. jejuni and exhibit signatures of NET generation, including presence of protein arginine deiminase-4, histone citrullination, myeloperoxidase, neutrophil elastase release and DNA extrusion. Production of NETs correlated with C. jejuni phagocytosis/endocytosis and invasion of neutrophils suggesting that host- and bacterial-mediated activities are responsible for NET induction. Further, NET-like structures were observed within intestinal tissue of C. jejuni-infected ferrets. Finally, induction of NETs significantly increased human colonocyte cytotoxicity, indicating that NET formation during C. jejuni infection may contribute to observed tissue pathology. These findings provide further understanding of C. jejuni-neutrophil interactions and inflammatory responses during campylobacteriosis.

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.

Microbe-MUC1 Crosstalk in Cancer-Associated Infections

Infection-associated cancers account for ∼20% of all malignancies. Understanding the molecular mechanisms underlying infection-associated malignancies may help in developing diagnostic biomarkers and preventative vaccines against malignancy. During infection, invading microbes interact with host mucins lining the glandular epithelial cells and trigger inflammation. MUC1 is a transmembrane mucin glycoprotein that is present on the surface of almost all epithelial cells, and is known to interact with invading microbes. This interaction can trigger pro- or anti-inflammatory responses depending on the microbe and the cell type. In this review we summarize the mechanisms of microbe and MUC1 interactions, and highlight how MUC1 plays contrasting roles in different cells. We also share perspectives on future research that may support clinical advances in infection-associated cancers.

Human Immunity Against Campylobacter Infection

Campylobacter is a worldwide foodborne pathogen, associated with human gastroenteritis. The efficient translocation of Campylobacter and its ability to secrete toxins into host cells are the 2 key features of Campylobacter pathophysiology which trigger inflammation in intestinal cells and contribute to the development of gastrointestinal symptoms, particularly diarrhoea, in humans. The purpose of conducting this literature review is to summarise the current understanding of: i) the human immune responses involved in the elimination of Campylobacter infection and ii) the resistance potential in Campylobacter against these immune responses. This review has highlighted that the intestinal epithelial cells are the preliminary cells which sense Campylobacter cells by means of their cell-surface and cytosolic receptors, activate various receptors-dependent signalling pathways, and recruit the innate immune cells to the site of inflammation. The innate immune system, adaptive immune system, and networking between these systems play a crucial role in bacterial clearance. Different cellular constituents of Campylobacter, mainly cell membrane lipooligosaccharides, capsule, and toxins, provide protection to Campylobacter against the human immune system mediated killing. This review has also identified gaps in knowledge, which are related to the activation of following during Campylobacter infection: i) cathelicidins, bactericidal permeability-increasing proteins, chemokines, and inflammasomes in intestinal epithelial cells; ii) siglec-7 receptors in dendritic cell; iii) acute phase proteins in serum; and iv) T-cell subsets in lymphoid nodules. This review evaluates the existing literature to improve the understanding of human immunity against Campylobacter infection and identify some of the knowledge gaps for future research.

A Gallus gallus Model for Determining Infectivity of Zoonotic Campylobacter

To better understand public health implications of waterfowl as reservoirs for zoonotic sources of Campylobacter in recreational waters, we developed a Gallus gallus (chick) model of infection to assess the pathogenicity of environmental isolates of Campylobacter. This method involved exposure of 1-day-old chicks through ingestion of water, the natural route of infection. Viable Campylobacter from laboratory-infected animals were monitored by using a modified non-invasive sampling of fresh chick excreta followed by a passive polycarbonate-filter migration culture assay. The method was used to evaluate the infectivities of three laboratory strains of Campylobacter spp. (Campylobacter coli, Campylobacter jejuni, and Campylobacter lari), three clinical isolates of C. jejuni, and four environmental Campylobacter spp. isolated from California gulls (Larus californicus). The results revealed that chicks were successfully infected with all laboratory and clinical isolates of Campylobacter spp. through ingestion of Campylobacter-spiked water, with infection rates ranging from <10 to >90% in a dose-dependent manner. More importantly, exposure of chicks with Campylobacter spp. isolated from Gallus gallus excreta also resulted in successful establishment of infection (≤90%). Each monitored Campylobacter spp. contained ≥7.5 × 10⁴ CFU⋅g^–1 of feces 7 days post-exposure. These results suggest that a G. gallus model can be used to assess infectivity of Campylobacter isolates, including gull and human clinical isolates. Use of an avian animal model can be applied to assess the importance of birds, such as the G. gallus, as potential contributors of waterborne-associated outbreaks of campylobacteriosis.

Investigating the Suitability of a Laboratory Mouse Model to Study the Pathogenesis of Abortifacient Campylobacter jejuni

The aim of this study was to assess whether pregnant mice represent a useful model to study the reproductive pathology of Campylobacter jejuni IA3902 using the end point of positive microbial culture of the organism from the fetoplacental unit. Pregnant BALB/c and CD-1 mice (14 days' gestation) were inoculated orally and intraperitoneally (IP) with 1 × 10⁹ colony-forming units/ml of C. jejuni IA3902. The organism was recovered by microbial culture from the fetoplacental unit in 10 of 10 BALB/c and 10 of 10 CD-1 IP-inoculated pregnant mice and in 29% (2/7) BALB/c and 38% (3/8) CD-1 orally inoculated pregnant mice. Gross reproductive lesions included necrosuppurative placentitis, fetal resorption, intrauterine fetal death, stillborn pups (dead neonates), and multifocal hepatitis. Histological changes consisted of locally extensive neutrophilic and necrotizing placentitis with intralesional bacterial colonies of C. jejuni, ulcerative endometritis, random multifocal hepatitis, and rare cholecystitis. Immunohistochemistry for the major outer membrane protein of C. jejuni revealed moderate to large numbers of the organism at the periphery of the placental discs, within trophoblasts and extracellularly, with invasion into the placental disc largely via the vascular network. The organism is trophic for neutral mucin, iron, and L-fucose within the murine placenta. C. jejuni IA3902 has affinity for the murine reproductive tract, specifically the fetoplacental unit, where it results in a necrotizing placentitis with positive microbial recovery after both IP and oral challenge in BALB/c and CD-1 pregnant mice.

Impact of Eimeria tenella Coinfection on Campylobacter jejuni Colonization of the Chicken

Eimeria tenella can cause the disease coccidiosis in chickens. The direct and often detrimental impact of this parasite on chicken health, welfare, and productivity is well recognized; however, less is known about the secondary effects that infection may have on other gut pathogens. Campylobacter jejuni is the leading cause of human bacterial foodborne disease in many countries and has been demonstrated to exert negative effects on poultry welfare and production in some broiler lines. Previous studies have shown that concurrent Eimeria infection can influence the colonization and replication of bacteria, such as Clostridium perfringens and Salmonella enterica serovar Typhimurium. Through a series of in vivo coinfection experiments, this study evaluated the impact that E. tenella infection had on C. jejuni colonization of chickens, including the influence of variations in parasite dose and sampling time after bacterial challenge. Coinfection with E. tenella resulted in a significant increase in C. jejuni colonization in the cecum in a parasite dose-dependent manner but a significant decrease in C. jejuni colonization in the spleen and liver of chickens. The results were reproducible at 3 and 10 days after bacterial infection. This work highlights that E. tenella not only has a direct impact on the health and well-being of chickens but can have secondary effects on important zoonotic pathogens.

Control of bacterial colonization in the glands and crypts

The epithelial cell layer of the major organs of the mammalian gastrointestinal (GI) tract is extensively invaginated into thousands of gland and crypt structures. These are lined by distinct sets of epithelial cells and may comprise discrete niches. The host maximizes the distance between the epithelial cell layer and GI-inhabiting microbes to limit inflammation, and these strategies also likely keep bacteria out of the glands and crypts. We discuss here the specific host processes that have been shown to restrict bacterial presence in the glands and crypts, specifically the immune system, acid, mucin, oxygen, and reactive oxygen species. Not surprisingly, microbes have evolved sophisticated strategies to overcome these host factors and reside close to the epithelium in the glands and crypts. Bacterial properties important for gland and crypt colonization include bacterial immunomodulatory molecules, chemotaxis, and the use of certain metabolites. Overall, these as-yet limited studies suggest there are specific host and bacterial properties that control gland and crypt colonization, contributing to the overall microbial spatial organization of the GI tract. However, there remains much to be discovered in this area.

Campylobacter jejuni bile exposure influences outer membrane vesicles protein content and bacterial interaction with epithelial cells

Campylobacter jejuni is a prevalent human pathogen and a major cause of bacterial gastroenteritis in the world. In humans, C. jejuni colonizes the intestinal tract and its tolerance to bile is crucial for bacteria to survive and establish infection. C. jejuni produces outer membrane vesicles (OMVs) which have been suggested to be involved in virulence. In this study, the proteome composition of C. jejuni OMVs in response to low concentration of bile was investigated. We showed that exposure of C. jejuni to low concentrations of bile, similar to the concentration in cecum, induced significant changes in the protein profile of OMVs released during growth without affecting the protein profile of the bacteria. This suggests that bile influences a selective packing of the OMVs after bacterial exposure to low bile. A low concentration of bile was found to increase bacterial adhesion to intestinal epithelial cells, likely by an enhanced hydrophobicity of the cell membrane following exposure to bile. The increased bacterial adhesiveness was not associated with increased invasion, instead bile exposure decreased C. jejuni invasion. OMVs released from bacteria upon exposure to low bile showed to increase both adhesion and invasion of non-bile-exposed bacteria into intestinal epithelial cells. These findings suggest that C. jejuni in environments with low concentrations of bile produce OMVs that facilitates colonization of the bacteria, and this could potentially contribute to virulence of C. jejuni in the gut.

Proteome Profiling by Label-Free Mass Spectrometry Reveals Differentiated Response of Campylobacter jejuni 81-176 to Sublethal Concentrations of Bile Acids

Purpose

Bile acids are crucial components of the intestinal antimicrobial defense and represent a significant stress factor for enteric pathogens. Adaptation processes of Campylobacter jejuni to this hostile environment are analyzed in this study by a proteomic approach.

Experimental design

Proteome profiling by label‐free mass spectrometry (SWATH‐MS) has been used to characterize the adaptation of C. jejuni to sublethal concentrations of seven bile acids.

Results

The bile acids with the lowest inhibitory concentration (IC₅₀), deoxycholic and chenodeoxycholic acid, induce the most significant proteome changes. Overall a downregulation of all basic biosynthetic pathways and a general decrease in the transcription machinery are found. Concurrently, an induction of factors involved in detoxification of reactive oxygen species, protein folding, and bile acid exporting efflux pumps is detected. Exposure to deoxycholic and chenodeoxycholic acid results in an increased expression of components of the more energy‐efficient aerobic respiration pathway, while the anaerobic branches of the electron transport chain are down‐expressed.

Conclusions and clinical relevance

The results show that C. jejuni has a differentiated system of adaptation to bile acid stresses. The findings enhance the understanding of the pathogenesis of campylobacteriosis, especially for survival of C. jejuni in the human intestine, and may provide clues to future medical treatment.

A novel mouse model of Campylobacter jejuni enteropathy and diarrhea

Campylobacter infections are among the leading bacterial causes of diarrhea and of 'environmental enteropathy' (EE) and growth failure worldwide. However, the lack of an inexpensive small animal model of enteric disease with Campylobacter has been a major limitation for understanding its pathogenesis, interventions or vaccine development. We describe a robust standard mouse model that can exhibit reproducible bloody diarrhea or growth failure, depending on the zinc or protein deficient diet and on antibiotic alteration of normal microbiota prior to infection. Zinc deficiency and the use of antibiotics create a niche for Campylobacter infection to establish by narrowing the metabolic flexibility of these mice for pathogen clearance and by promoting intestinal and systemic inflammation. Several biomarkers and intestinal pathology in this model also mimic those seen in human disease. This model provides a novel tool to test specific hypotheses regarding disease pathogenesis as well as vaccine development that is currently in progress.

Campylobacter jejuni and associated immune mechanisms: short-term effects and long-term implications for infants in low-income countries

PURPOSE OF REVIEW

Campylobacter jejuni is recognized as one of the most common causes of food-borne gastrointestinal illness worldwide, resulting in a self-limiting dysentery in developed countries. However, it is increasingly gaining attention due to its association with postinfectious complications such as Guillain-Barré Syndrome and recently recognized importance in early childhood diarrhea in developing countries. We hypothesize that the inflammation mediated by C. jejuni infection causes environmental enteric dysfunction, and with contribution from diet and the host, microbiome may be responsible for growth faltering in children and developmental disability.

RECENT FINDINGS

Diet plays a major role in the impact of C. jejuni infection, both by availability of micronutrients for the bacteria and host as well as shaping the microbiome that affords resistance. Early childhood repeated exposure to the bacterium results in inflammation that affords long-term immunity but, in the short term, can lead to malabsorption, oral vaccine failure, cognitive delay and increased under-5 mortality.

SUMMARY

As interest in C. jejuni increases, our understanding of its virulence mechanisms has improved. However, much work remains to be done to fully understand the implications of immune-mediated inflammation and its potential role in diseases such as environmental enteric dysfunction.

Metabolic and fitness determinants for in vitro growth and intestinal colonization of the bacterial pathogen Campylobacter jejuni

Campylobacter jejuni is one of the leading infectious causes of food-borne illness around the world. Its ability to persistently colonize the intestinal tract of a broad range of hosts, including food-producing animals, is central to its epidemiology since most infections are due to the consumption of contaminated food products. Using a highly saturated transposon insertion library combined with next-generation sequencing and a mouse model of infection, we have carried out a comprehensive genome-wide analysis of the fitness determinants for growth in vitro and in vivo of a highly pathogenic strain of C. jejuni. A comparison of the C. jejuni requirements to colonize the mouse intestine with those necessary to grow in different culture media in vitro, combined with isotopologue profiling and metabolic flow analysis, allowed us to identify its metabolic requirements to establish infection, including the ability to acquire certain nutrients, metabolize specific substrates, or maintain intracellular ion homeostasis. This comprehensive analysis has identified metabolic pathways that could provide the basis for the development of novel strategies to prevent C. jejuni colonization of food-producing animals or to treat human infections.

Analysis of Campylobacter jejuni infection in the gnotobiotic piglet and genome-wide identification of bacterial factors required for infection

To investigate how Campylobacter jejuni causes the clinical symptoms of diarrhoeal disease in humans, use of a relevant animal model is essential. Such a model should mimic the human disease closely in terms of host physiology, incubation period before onset of disease, clinical signs and a comparable outcome of disease. In this study, we used a gnotobiotic piglet model to study determinants of pathogenicity of C. jejuni. In this model, C. jejuni successfully established infection and piglets developed an increased temperature with watery diarrhoea, which was caused by a leaky epithelium and reduced bile re-absorption in the intestines. Further, we assessed the C. jejuni genes required for infection of the porcine gastrointestinal tract utilising a transposon (Tn) mutant library screen. A total of 123 genes of which Tn mutants showed attenuated piglet infection were identified. Our screen highlighted a crucial role for motility and chemotaxis, as well as central metabolism. In addition, Tn mutants of 14 genes displayed enhanced piglet infection. This study gives a unique insight into the mechanisms of C. jejuni disease in terms of host physiology and contributing bacterial factors.

The Helical Shape of Campylobacter jejuni Promotes In Vivo Pathogenesis by Aiding Transit through Intestinal Mucus and Colonization of Crypts

Campylobacter jejuni is a helix-shaped enteric bacterial pathogen and a common cause of gastroenteritis. We recently developed a mouse model for this human pathogen utilizing the SIGIRR-deficient mouse strain, which exhibits significant intestinal inflammation in response to intestinal C. jejuni infection. In the current study, this mouse model was used to define whether C. jejuni's characteristic helical shape plays a role in its ability to colonize and elicit inflammation in the mouse intestine. Mice were infected with the previously characterized straight-rod Δpgp1 and Δpgp2 mutant strains, along with a newly characterized curved-rod Δ1228 mutant strain. We also compared the resultant infections and pathology to those elicited by the helix-shaped wild-type C. jejuni and complemented strains. Despite displaying wild-type colonization of the intestinal lumen, the straight-rod Δpgp1 and Δpgp2 mutants were essentially nonpathogenic, while all strains with a curved or helical shape retained their expected virulence. Furthermore, analysis of C. jejuni localization within the ceca of infected mice determined that the primary difference between the rod-shaped, nonpathogenic mutants and the helix-shaped, pathogenic strains was the ability to colonize intestinal crypts. Rod-shaped mutants appeared unable to colonize intestinal crypts due to an inability to pass through the intestinal mucus layer to directly contact the epithelium. Together, these results support a critical role for C. jejuni's helical morphology in enabling it to traverse and colonize the mucus-filled intestinal crypts of their host, a necessary step required to trigger intestinal inflammation in response to C. jejuni.

Insights into Campylobacter jejuni colonization and enteritis using a novel infant rabbit model

A lack of relevant disease models for Campylobacter jejuni has long been an obstacle to research into this common enteric pathogen. Here we used an infant rabbit to study C. jejuni infection, which enables us to define several previously unknown but key features of the organism. C. jejuni is capable of systemic invasion in the rabbit, and developed a diarrhea symptom that mimicked that observed in many human campylobacteriosis. The large intestine was the most consistently colonized site and produced intestinal inflammation, where specific cytokines were induced. Genes preferentially expressed during C. jejuni infection were screened, and acs, cj1385, cj0259 seem to be responsible for C. jejuni invasion. Our results demonstrates that the infant rabbit can be used as an alternative experimental model for the study of diarrheagenic Campylobacter species and will be useful in exploring the pathogenesis of other related pathogens.