In vivo phase variation and serologic response to lipooligosaccharide of Campylobacter jejuni in experimental human infection

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Microbial lectome versus host glycolipidome: How pathogens exploit glycosphingolipids to invade, dupe or kill

Glycosphingolipids (GSLs) are ubiquitous components of the cell membranes, found across several kingdoms of life, from bacteria to mammals, including humans. GSLs are a subclass of major glycolipids occurring in animal lipid membranes in clusters named “lipid rafts.” The most crucial functions of GSLs include signal transduction and regulation as well as participation in cell proliferation. Despite the mainstream view that pathogens rely on protein–protein interactions to survive and thrive in their hosts, many also target the host lipids. In particular, multiple pathogens produce adhesion molecules or toxins that bind GSLs. Attachment of pathogens to cell surface receptors is the initial step in infections. Many mammalian pathogens have evolved to recognize GSL-derived receptors. Animal glycosphingolipidomes consist of multiple types of GSLs differing in terminal glycan and ceramide structures in a cell or tissue-specific manner. Interspecies differences in GSLs dictate host specificity as well as cell and tissue tropisms. Evolutionary pressure exerted by pathogens on their hosts drives changes in cell surface glycoconjugates, including GSLs, and has produced a vast number of molecules and interaction mechanisms. Despite that abundance, the role of GSLs as pathogen receptors has been largely overlooked or only cursorily discussed. In this review, we take a closer look at GSLs and their role in the recognition, cellular entry, and toxicity of multiple bacterial, viral and fungal pathogens.

Stabilizing Genetically Unstable Simple Sequence Repeats in the Campylobacter jejuni Genome by Multiplex Genome Editing: a Reliable Approach for Delineating Multiple Phase-Variable Genes

Hypermutable simple sequence repeats (SSRs) are major drivers of phase variation in Campylobacter jejuni. The presence of multiple SSR-mediated phase-variable genes encoding enzymes that modify surface structures, including capsular polysaccharide (CPS) and lipooligosaccharide (LOS), generates extreme cell surface diversity within bacterial populations, thereby promoting adaptation to selective pressures in host environments. Therefore, genetically controlling SSR-mediated phase variation can be important for achieving stable and reproducible research on C. jejuni. Here, we show that natural "cotransformation" is an effective method for C. jejuni genome editing. Cotransformation is a trait of naturally competent bacteria that causes uptake/integration of multiple different DNA molecules, which has been recently adapted to multiplex genome editing by natural transformation (MuGENT), a method for introducing multiple mutations into the genomes of these bacteria. We found that cotransformation efficiently occurred in C. jejuni. To examine the feasibility of MuGENT in C. jejuni, we "locked" different polyG SSR tracts in strain NCTC11168 (which are located in the biosynthetic CPS/LOS gene clusters) into either the ON or OFF configurations. This approach, termed "MuGENT-SSR," enabled the generation of all eight edits within 2 weeks and the identification of a phase-locked strain with a highly stable type of Penner serotyping, a CPS-based serotyping scheme. Furthermore, extensive genome editing of this strain by MuGENT-SSR identified a phase-variable gene that determines the Penner serotype of NCTC11168. Thus, MuGENT-SSR provides a platform for genetic and phenotypic engineering of genetically unstable C. jejuni, making it a reliable approach for elucidating the mechanisms underlying phase-variable expression of specific phenotypes. IMPORTANCE Campylobacter jejuni is the leading bacterial cause of foodborne gastroenteritis in developed countries and occasionally progresses to the autoimmune disease Guillain-Barré syndrome. A relatively large number of hypermutable simple sequence repeat (SSR) tracts in the C. jejuni genome markedly decreases its phenotypic stability through reversible changes in the ON or OFF expression states of the genes in which they reside, a phenomenon called phase variation. Thus, controlling SSR-mediated phase variation can be important for achieving stable and reproducible research on C. jejuni. In this study, we developed a feasible and effective approach for genetically manipulate multiple SSR tracts in the C. jejuni genome using natural cotransformation, a trait of naturally transformable bacterial species that causes the uptake and integration of multiple different DNA molecules. This approach will greatly help to improve the genetic and phenotypic stability of C. jejuni to enable diverse applications in research and development.

Vaccines for Protecting Infants from Bacterial Causes of Diarrheal Disease

The global diarrheal disease burden for Shigella, enterotoxigenic Escherichia coli (ETEC), and Campylobacter is estimated to be 88M, 75M, and 75M cases annually, respectively. A vaccine against this target trio of enteric pathogens could address about one-third of diarrhea cases in children. All three of these pathogens contribute to growth stunting and have demonstrated increasing resistance to antimicrobial agents. Several combinations of antigens are now recognized that could be effective for inducing protective immunity against each of the three target pathogens in a single vaccine for oral administration or parenteral injection. The vaccine combinations proposed here would result in a final product consistent with the World Health Organization's (WHO) preferred product characteristics for ETEC and Shigella vaccines, and improve the vaccine prospects for support from Gavi, the Vaccine Alliance, and widespread uptake by low- and middle-income countries' (LMIC) public health stakeholders. Broadly protective antigens will enable multi-pathogen vaccines to be efficiently developed and cost-effective. This review describes how emerging discoveries for each pathogen component of the target trio could be used to make vaccines, which could help reduce a major cause of poor health, reduced cognitive development, lost economic productivity, and poverty in many parts of the world.

Effects of antibiotic resistance (AR) and microbiota shifts on Campylobacter jejuni-mediated diseases

Campylobacter jejuni is an important zoonotic pathogen recently designated a serious antimicrobial resistant (AR) threat. While most patients with C. jejuni experience hemorrhagic colitis, serious autoimmune conditions can follow including inflammatory bowel disease (IBD) and the acute neuropathy Guillain Barré Syndrome (GBS). This review examines inter-relationships among factors mediating C. jejuni diarrheal versus autoimmune disease especially AR C. jejuni and microbiome shifts. Because both susceptible and AR C. jejuni are acquired from animals or their products, we consider their role in harboring strains. Inter-relationships among factors mediating C. jejuni colonization, diarrheal and autoimmune disease include C. jejuni virulence factors and AR, the enteric microbiome, and host responses. Because AR C. jejuni have been suggested to affect the severity of disease, length of infections and propensity to develop GBS, it is important to understand how these interactions occur when strains are under selection by antimicrobials. More work is needed to elucidate host-pathogen interactions of AR C. jejuni compared with susceptible strains and how AR C. jejuni are maintained and evolve in animal reservoirs and the extent of transmission to humans. These knowledge gaps impair the development of effective strategies to prevent the emergence of AR C. jejuni in reservoir species and human populations.

Guillain Barré Syndrome is induced in Non-Obese Diabetic (NOD) mice following Campylobacter jejuni infection and is exacerbated by antibiotics

Campylobacter jejuni is a leading cause of bacterial gastroenteritis linked to several serious autoimmune sequelae such as the peripheral neuropathies Guillain Barré syndrome (GBS) and Miller Fisher syndrome (MFS). We hypothesized that GBS and MFS can result in NOD wild type (WT) mice or their congenic interleukin (IL)-10 or B7-2 knockouts secondary to C. jejuni infection. Mice were gavaged orally with C. jejuni strains HB93-13 and 260.94 from patients with GBS or CF93-6 from a patient with MFS and assessed for clinical neurological signs and phenotypes, anti-ganglioside antibodies, and cellular infiltrates and lesions in gut and peripheral nerve tissues. Significant increases in autoantibodies against single gangliosides (GM1, GQ1b, GD1a) occurred in infected NOD mice of all genotypes, although the isotypes varied (NOD WT had IgG1, IgG3; NOD B7-2^-/- had IgG3; NOD IL-10^-/- had IgG1, IgG3, IgG2a). Infected NOD WT and NOD IL-10^-/- mice also produced anti-ganglioside antibodies of the IgG1 isotype directed against a mixture of GM1/GQ1b gangliosides. Phenotypic tests showed significant differences between treatment groups of all mouse genotypes. Peripheral nerve lesions with macrophage infiltrates were significantly increased in infected mice of NOD WT and IL-10^-/- genotypes compared to sham-inoculated controls, while lesions with T cell infiltrates were significantly increased in infected mice of the NOD B7-2^-/- genotype compared to sham-inoculated controls. In both infected and sham inoculated NOD IL-10^-/- mice, antibiotic treatment exacerbated neurological signs, lesions and the amount and number of different isotypes of antiganglioside autoantibodies produced. Thus, inducible mouse models of post-C. jejuni GBS are feasible and can be characterized based on evaluation of three factors-onset of GBS clinical signs/phenotypes, anti-ganglioside autoantibodies and nerve lesions. Based on these factors we characterized 1) NOD B-7^-/- mice as an acute inflammatory demyelinating polyneuropathy (AIDP)-like model, 2) NOD IL-10^-/- mice as an acute motor axonal neuropathy (AMAN)-like model best employed over a limited time frame, and 3) NOD WT mice as an AMAN model with mild clinical signs and lesions. Taken together these data demonstrate that C. jejuni strain genotype, host genotype and antibiotic treatment affect GBS disease outcomes in mice and that many disease phenotypes are possible.

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.

Immune responses to Campylobacter (C. jejuni or C. coli) infections: a two-year study of US forces deployed to Thailand

Campylobacter spp. is a leading cause of diarrheal disease among US troops deployed to Thailand for exercise. We investigated the importance of immunological analysis and immune responses against Campylobacter infection in US troops deployed to Thailand. Blood and fecal samples were collected from volunteered soldiers with diarrhea and from healthy controls. Stool culture was performed to identify the pathogens. Campylobacter-specific antibodies, antibody secreting cells and cytokines were measured. Several bacterial protein fragments in the outer membrane extract of Campylobacter spp., were identified by an immunoblot analysis with plasma and fecal antibodies. Among all of the diarrheal cases, 35% were Campylobacter-positive. Based on antibody titers in plasma and in fecal extract and antibody secreting cells: 6% of healthy controls, 32% of the Campylobacter culture-negative diarrheal cases, and 85% of the Campylobacter culture-positive diarrheal cases were positive for Campylobacter. Our results indicate that the measurement of Campylobacter-specific antibodies in plasma and fecal extract samples is a good marker of exposure to Campylobacter, and this test may be a useful diagnostic tool for seroepidemiological studies. Elicited antibodies against several bacterial outer membrane protein fragments suggest that these protein fragments are vital in providing protective immunity against Campylobacter.

Genomic and global approaches to unravelling how hypermutable sequences influence bacterial pathogenesis

Rapid adaptation to fluctuations in the host milieu contributes to the host persistence and virulence of bacterial pathogens. Adaptation is frequently mediated by hypermutable sequences in bacterial pathogens. Early bacterial genomic studies identified the multiplicity and virulence-associated functions of these hypermutable sequences. Thus, simple sequence repeat tracts (SSRs) and site-specific recombination were found to control capsular type, lipopolysaccharide structure, pilin diversity and the expression of outer membrane proteins. We review how the population diversity inherent in the SSR-mediated mechanism of localised hypermutation is being unlocked by the investigation of whole genome sequences of disease isolates, analysis of clinical samples and use of model systems. A contrast is presented between the problematical nature of analysing simple sequence repeats in next generation sequencing data and in simpler, pragmatic PCR-based approaches. Specific examples are presented of the potential relevance of this localized hypermutation to meningococcal pathogenesis. This leads us to speculate on the future prospects for unravelling how hypermutable mechanisms may contribute to the transmission, spread and persistence of bacterial pathogens.

Campylobacter jejuni strain discrimination and temperature-dependent glycome expression profiling by lectin microarray

Gram-negative Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans worldwide and the most frequently identified infectious trigger in patients developing Guillain-Barré syndrome (GBS). While C. jejuni is pathogenic in humans, it is a commensal in avian hosts. Bacterial cell surface carbohydrates are important virulence factors and play roles in adherence, colonisation and infection. The mechanisms leading to infection or persistent colonisation of C. jejuni are not well understood but host temperature may provide an important stimulus for specific adaptation. Thus, examination of the modulation of the total surface glycome of C. jejuni in response to temperature may help shed light on commensal and pathogenic mechanisms for this species. C. jejuni strains 81116 and 81-176 were cultured at 37 and 42°C to simulate human and avian host conditions, respectively, and whole cells were profiled on lectin microarrays constructed to include a wide range of binding specificities. C. jejuni 81116 profiles indicated that the previously characterised lipopolysaccharide (LPS)-like molecule and N-linked glycans were the predominantly recognised cell surface structures while capsular polysaccharide (CPS), lipooligosaccharides (LOS) and N-linked glycosylation were best recognised for strain 81-176 at 37°C. The profiles of both strains varied and were distinguishable at both temperatures. At the higher temperature, reduced dominance of the LPS-like structure was associated with strain 81116 and a change in the relative distribution of CPS and LOS structures was indicated for strain 81-176. This change in LOS molecular mass species distribution between temperatures was confirmed by SDS-PAGE analysis. Additionally, opposite behaviour of certain lectins was noted between the plate agglutination assay and the microarray platform. Insights into the important glycosylation involved in C. jejuni host cell tropism at different growth temperatures were gained using the lectin microarray platform.

Sialylation of Campylobacter jejuni endotoxin promotes dendritic cell-mediated B cell responses through CD14-dependent production of IFN-β and TNF-α

Campylobacter jejuni is the most common bacterial cause of human gastroenteritis and often precedes development of Guillain-Barré syndrome (GBS), a life-threatening paralytic disease. The incorporation of the carbohydrate sialic acid into C. jejuni lipooligosaccharides (LOS) is associated with increased severity of gastroenteritis and with induction of GBS; however, the underlying mechanisms remain completely unknown. In this study, we demonstrate that sialic acids in C. jejuni endotoxin enhance the rapid production of IFN-β and TNF-α by human dendritic cells (DCs). Using neutralizing Abs and receptors it was shown that these DC-derived cytokines promote the proliferation of human mucosal B cells in a T cell-independent manner. The production of both IFN-β and TNF-α by DCs in response to LOS requires CD14, and the amplified response of DCs to sialylated C. jejuni LOS is CD14 dependent. Together, these results indicate that sialylation of C. jejuni LOS increases DC activation and promotes subsequent B cell responses through CD14-driven production of IFN-β and TNF-α. This enhanced DC/B cell response may explain the increased pathogenicity of sialylated C. jejuni and may be key to the initiation of B cell-mediated autoimmunity in GBS.

A "successful allele" at Campylobacter jejuni contingency locus Cj0170 regulates motility; "successful alleles" at locus Cj0045 are strongly associated with mouse colonization

Campylobacter jejuni is an important foodborne pathogen of humans and its primary reservoir is the gastrointestinal (GI) tract of chickens. Our previous studies demonstrated that phase variation to specific "successful alleles" at C. jejuni contingency loci Cj0045 (successful alleles carry 9G or 10G homopolymeric tracts) and Cj0170 (successful allele carries a 10G homopolymeric tract) in C. jejuni populations is strongly associated with colonization and enteritis in C57BL/6 IL-10 deficient mice. In the current study, we strengthened the association between locus Cj0170, Cj0045, and mouse colonization. We generated 8 independent strains derived from C. jejuni 11168 strain KanR4 that carried a Cj0170 gene disruption and these were all non motile. Two randomly chosen strains with the Cj0170 gene disruption (DM0170-2 and DM0170-6) were gavaged into mice. DM0170-2 and DM0170-6 failed to colonize mice while the control strain that carried a "successful"Cj0170 10G allele was motile and did colonize mice. In parallel studies, when we inoculated C. jejuni strain 33292 into mice, the "unsuccessful"Cj0045 11G allele experienced phase variation to "successful" 9G and 10G alleles in 2 independent experiments prior to d4 post inoculation in mice while the "successful" 9G allele in the control strain remained stable through d21 post inoculation or shifted to other successful alleles. These data confirm that locus Cj0170 regulates motility in C. jejuni strain KanR4 and is a virulence factor in the mouse model. The data also support a possible role of locus Cj0045 as a virulence factor in strain 33292 in infection of mice.

Charles JL, Buffa BA, Brooks AP, Poe SA, Eaton KA, Stanhope MJ, Mansfield LS. Outcome of infection of C57BL/6 IL-10(-/-) mice with Campylobacter jejuni strains is correlated with genome content of open reading frames up- and down-regulated in vivo

Human Campylobacter jejuni infection can result in an asymptomatic carrier state, watery or bloody diarrhea, bacteremia, meningitis, or autoimmune neurological sequelae. Infection outcomes of C57BL/6 IL-10(-/-) mice orally infected with twenty-two phylogenetically diverse C. jejuni strains were evaluated to correlate colonization and disease phenotypes with genetic composition of the strains. Variation between strains was observed in colonization, timing of development of clinical signs, and occurrence of enteric lesions. Five pathotypes of C. jejuni in C57BL/6 IL-10(-/-) mice were delineated: little or no colonization, colonization without disease, colonization with enteritis, colonization with hemorrhagic enteritis, and colonization with neurological signs with or without enteritis. Virulence gene content of ten sequenced strains was compared in silico; virulence gene content of twelve additional strains was compared using a C. jejuni pan-genome microarray. Neither total nor virulence gene content predicted pathotype; nor was pathotype correlated with multilocus sequence type. Each strain was unique with regard to absences of known virulence-related loci and/or possession of point mutations and indels, including phase variation, in virulence-related genes. An experiment in C. jejuni 11168-infected germ-free mice showed that expression levels of ninety open reading frames (ORFs) were significantly up- or down-regulated in the mouse cecum at least two-fold compared to in vitro growth. Genomic content of these ninety C. jejuni 11168 ORFs was significantly correlated with the capacity to colonize and cause enteritis in C57BL/6 IL-10(-/-) mice. Differences in gene expression levels and patterns are thus an important determinant of pathotype in C. jejuni strains in this mouse model.

Human challenge studies: a review of adequacy of reporting methods and results

Since the 1940s, researchers have purposefully infected healthy adult humans with pathogenic organisms to study how these pathogens cause disease and can be treated and prevented. 'Challenge studies' can be safe, ethical, extremely informative and an efficient use of resources during the clinical development of vaccines, but knowledge of this form of clinical research trial is not widespread. A review of the human challenge literature was performed to determine whether common elements of challenge studies can be identified in the articles published to date. The review demonstrated incomplete reporting of study characteristics deemed necessary for the correct interpretation and application of human challenge study results and for the accurate replication of study methodology. An unofficial extension of the Consolidated Standards of Reporting Trials (CONSORT) statement is proposed.

Genetic diversity in Campylobacter jejuni is associated with differential colonization of broiler chickens and C57BL/6J IL10-deficient mice

Previous studies have demonstrated that Campylobacter jejuni, the leading causative agent of bacterial food-borne disease in the USA, exhibits high-frequency genetic variation that is associated with changes in cell-surface antigens and ability to colonize chickens. To expand our understanding of the role of genetic diversity in the disease process, we analysed the ability of three C. jejuni human disease isolates (strains 11168, 33292 and 81-176) and genetically marked derivatives to colonize Ross 308 broilers and C57BL/6J IL10-deficient mice. C. jejuni colonized broilers at much higher efficiency (all three strains, 23 of 24 broilers) than mice (11168 only, 8 of 24 mice). C. jejuni 11168 genetically marked strains colonized mice at very low efficiency (2 of 42 mice); however, C. jejuni reisolated from mice colonized both mice and broilers at high efficiency, suggesting that this pathogen can adapt genetically in the mouse. We compared the genome composition in the three wild-type C. jejuni strains and derivatives by microarray DNA/DNA hybridization analysis; the data demonstrated a high degree of genetic diversity in three gene clusters associated with synthesis and modification of the cell-surface structures capsule, flagella and lipo-oligosaccharide. Finally, we analysed the frequency of mutation in homopolymeric tracts associated with the contingency genes wlaN (GC tract) and flgR (AT tracts) in culture and after passage through broilers and mice. C. jejuni adapted genetically in culture at high frequency and the degree of genetic diversity was increased by passage through broilers but was nearly eliminated in the gastrointestinal tract of mice. The data suggest that the broiler gastrointestinal tract provides an environment which promotes outgrowth and genetic variation in C. jejuni; the enhancement of genetic diversity at this location may contribute to its importance as a human disease reservoir.

Assessment of the duration of protection in Campylobacter jejuni experimental infection in humans

A human Campylobacter jejuni infection model provided controlled exposure to assess vaccine efficacy and investigate protective immunity for this important diarrheal pathogen. A well-characterized outbreak strain, C. jejuni 81-176, was investigated using a volunteer experimental infection model to evaluate the dose range and duration of protection. Healthy Campylobacter-seronegative adults received C. jejuni strain 81-176 via oral inoculation of 10(5), 10(7), or 10(9) CFU (5 adults/dose), which was followed by clinical and immunological monitoring. Based on dose range clinical outcomes, the 10(9)-CFU dose (n = 31) was used to assess homologous protection at 28 to 49 days (short-term veterans [STV]; n = 8) or 1 year (long-term veterans [LTV]; n = 7) after primary infection. An illness dose effect was observed for naïve subjects (with lower doses, 40 to 60% of the subjects were ill; with the 10(9)-CFU dose, 92% of the subjects were ill) along with complete protection for the STV group and attenuated illness for the LTV group (57%). Partial resistance to colonization was seen in STV (25% of the subjects were not infected; 3-log-lower maximum excretion level). Systemic and mucosal immune responses were robust in naïve subjects irrespective of the dose or the severity of illness. In contrast, in STV there was a lack of circulating antibody-secreting cells (ASC), reflecting the local mucosal effector responses. LTV exhibited comparable ASC responses to primary infection, and anamnestic fecal IgA responses likely contributed to self-resolving illness prior to antibiotic treatment. Campylobacter antigen-dependent production of gamma interferon by peripheral blood mononuclear cells was strongly associated with protection from illness, supporting the hypothesis that TH1 polarization has a primary role in acquired immunity to C. jejuni. This study revealed a C. jejuni dose-related increase in campylobacteriosis rates, evidence of complete short-term protection that waned with time, and immune response patterns associated with protection.

The role of endotoxin in infection: Helicobacter pylori and Campylobacter jejuni

Both Helicobacter pylori and Campylobacter jejuni are highly prevalent Gram-negative microaerophilic bacteria which are gastrointestinal pathogens of humans; H. pylori colonizes the gastroduodenal compartment and C. jejuni the intestinal mucosa. Although H. pylori causes chronic gastric infection leading to gastritis, peptic ulcers and eventually gastric cancer while C. jejuni causes acute infection inducing diarrhoeal disease, the endotoxin molecules of both bacterial species contrastingly contribute to their pathogenesis and the autoimmune sequelae each induces. Compared with enterobacterial endotoxin, that of H. pylori has significantly lower endotoxic and immuno-activities, the molecular basis for which is the underphosphorylation and underacylation of the lipid A component that interacts with immune receptors. This induction of low immunological responsiveness by endotoxin may aid the prolongation of H. pylori infection and therefore infection chronicity. On the other hand, this contrasts with acute infection-causing C. jejuni where overt inflammation contributes to pathology and diarrhoea production, and whose endotoxin is immunologically and endotoxically active. Futhermore, both H. pylori and C. jejuni exhibit molecular mimicry in the saccharide components of their endotoxins which can induce autoreactive antibodies; H. pylori expresses mimicry of Lewis and some ABO blood group antigens, C. jejuni mimicry of gangliosides. The former has been implicated in influencing the development of inflammation and gastric atrophy (a precursor of gastic cancer), the latter is central to the development of the neurological disorder Guillain-Barré syndrome. Both diseases raise important questions concerning infection-induced autoimmunity awaiting to be addressed.

Immunity to Campylobacter: its role in risk assessment and epidemiology

Acquired immunity is an important factor in the epidemiology of campylobacteriosis in the developing world, apparently limiting symptomatic infection to children of less than two years. However, also in developed countries the highest incidence is observed in children under five years and the majority of Campylobacter infections are asymptomatic, which may be related to the effects of immunity and/or the ingested doses. Not accounting for immunity in epidemiological studies may lead to biased results due to the misclassification of Campylobacter-exposed but apparently healthy persons as unexposed. In risk assessment studies, health risks may be overestimated when immunity is neglected.

N-linked glycosylation in bacteria: an unexpected application

Traditionally, glycoproteins have been considered the exclusive property of eukaryotes and archaea, but it is now evident that glycoproteins are found in all domains of life. In recent years N-linked glycosylation among some epsilon-proteobacteria has emerged as a new and exciting research area and represents a useful model to understand this complex process in simple, genetically tractable bacteria. Above all, the transfer of N-linked glycosylation systems to the work-horse bacterium, Escherichia coli, has enabled, for the first time, the production of recombinant glycoproteins. This has potentially provided the option for tailor-made glycoproteins and has opened up the field of glycoengineering, particularly with respect to the development of glycoconjugate vaccines.

Update on Campylobacter jejuni vaccine development for preventing human campylobacteriosis

Campylobacteriosis constitutes a serious medical and socioeconomic problem worldwide. Rapidly increasing antibiotic resistance of bacterial strains compels us to develop alternative therapeutic strategies and to search for efficient immunoprophylactic methods. The vast majority of Campylobacter infections in developed countries occur as sporadic cases, mainly caused by eating undercooked Campylobacter-contaminated poultry. The most efficient strategy of decreasing the number of human Campylobacter infections is by implementing protective vaccinations for humans and/or chickens. Despite more than 10 years of research, an effective anti-Campylobacter vaccine has not been developed. This review highlights our increasing knowledge of Campylobacter interaction with host cells and focuses on recently published data describing the efficacy of anti-Campylobacter vaccine prototypes.

Multiple factors interact to produce responses resembling spectrum of human disease in Campylobacter jejuni infected C57BL/6 IL-10-/- mice

BACKGROUND

Campylobacter jejuni infection produces a spectrum of clinical presentations in humans--including asymptomatic carriage, watery diarrhea, and bloody diarrhea--and has been epidemiologically associated with subsequent autoimmune neuropathies. This microorganism is genetically variable and possesses genetic mechanisms that may contribute to variability in nature. However, relationships between genetic variation in the pathogen and variation in disease manifestation in the host are not understood. We took a comparative experimental approach to explore differences among different C. jejuni strains and studied the effect of diet on disease manifestation in an interleukin-10 deficient mouse model.

RESULTS

In the comparative study, C57BL/6 interleukin-10-/- mice were infected with seven genetically distinct C. jejuni strains. Four strains colonized the mice and caused disease; one colonized with no disease; two did not colonize. A DNA:DNA microarray comparison of the strain that colonized mice without disease to C. jejuni 11168 that caused disease revealed that putative virulence determinants, including loci encoding surface structures known to be involved in C. jejuni pathogenesis, differed from or were absent in the strain that did not cause disease. In the experimental study, the five colonizing strains were passaged four times in mice. For three strains, serial passage produced increased incidence and degree of pathology and decreased time to develop pathology; disease shifted from watery to bloody diarrhea. Mice kept on an ~6% fat diet or switched from an approximately 12% fat diet to an approximately 6% fat diet just before infection with a non-adapted strain also exhibited increased incidence and severity of disease and decreased time to develop disease, although the effects of diet were only statistically significant in one experiment.

CONCLUSION

C. jejuni strain genetic background and adaptation of the strain to the host by serial passage contribute to differences in disease manifestations of C. jejuni infection in C57BL/6 IL-10-/- mice; differences in environmental factors such as diet may also affect disease manifestation. These results in mice reflect the spectrum of clinical presentations of C. jejuni gastroenteritis in humans and contribute to usefulness of the model in studying human disease.

Identification of novel carbohydrate modifications on Campylobacter jejuni 11168 flagellin using metabolomics-based approaches

It is well known that the flagellin of Campylobacter jejuni is extensively glycosylated by pseudaminic acid and the related acetamindino derivative, in addition to flagellin glycosylation being essential for motility and colonization of host cells. Recently, the use of metabolomics permitted the unequivocal characterization of unique flagellin modifications in Campylobacter, including novel legionaminic acid sugars in Campylobacter coli, which had been impossible to ascertain in earlier studies using proteomics-based approaches. To date, the precise identities of the flagellin glycosylation modifications have only been elucidated for C. jejuni 81-176 and C. coli VC167 and those present in the first genome-sequenced strain C. jejuni 11168 remain elusive due to lability and respective levels of individual glycan modifications. We report the characterization of the carbohydrate modifications on C. jejuni 11168 flagellin using metabolomics-based approaches. Detected as their corresponding CMP-linked precursors, structural information on the flagellin modifications was obtained using a combination of MS and NMR spectroscopy. In addition to the pseudaminic acid and legionaminic acid sugars known to be present on Campylobacter flagellin, two unusual 2,3-di-O-methylglyceric acid modifications of a nonulosonate sugar were identified. By performing a metabolomic analysis of selected isogenic mutants of genes from the flagellin glycosylation locus of this pathogen, these novel CMP-linked precursors were confirmed to be di-O-methylglyceric acid derivatives of pseudaminic acid and the related acetamidino sugar. This is the first comprehensive analysis of the flagellar modifications in C. jejuni 11168 and structural elucidation of di-O-methylglyceric acid derivatives of pseudaminic acid on Campylobacter flagellin.

Correlation of proinflammatory and anti-inflammatory cytokine levels with histopathological changes in an adult mouse lung model of Campylobacter jejuni infection

Campylobacter jejuni is a major cause of diarrhea in humans. A mouse lung model of infection was previously established for C. jejuni. We used this model to study cytokine production in the lungs and correlated it with pathological changes. C. jejuni strain 81-176 or sterile phosphate-buffered saline was intranasally inoculated into adult BALB/c mice. The levels of proinflammatory cytokines (gamma interferon, tumor necrosis factor alpha, interleukin-1beta [IL-1beta], IL-2) and anti-inflammatory cytokines (IL-4, IL-10), in addition to those of IL-6, were assessed on days 1, 3, and 5 postinfection by enzyme-linked immunosorbent assay, and the ratios of proinflammatory cytokines to anti-inflammatory cytokines were calculated. Since IL-6 is unique in that it is both a proinflammatory cytokine and a TH2 cytokine, it was considered to be both in the determination of these ratios. The significance of the cytokine levels and ratios were determined by the Mann-Whitney U test (P<or=0.05). The induction of proinflammatory cytokines in the lungs of infected mice, as indicated by the cytokine levels and ratios, coincided with the accumulation of neutrophils and activated macrophages, in addition to the clearance of the bacterial load and bacteriumlike structures that we have previously shown in the same groups of mice. This was followed by increased levels of anti-inflammatory cytokines and the resolution of inflammation and pathology in the lungs. This study demonstrates the dynamics of cytokine production and their correlation with tissue inflammation and the resolution of infection. This model is useful for further studies of the pathogenesis of C. jejuni infection and vaccine evaluation.

Characterization of two Campylobacter jejuni strains for use in volunteer experimental-infection studies

The development of vaccines against Campylobacter jejuni would be facilitated by the ability to perform phase II challenge studies. However, molecular mimicry of the lipooligosaccharide (LOS) of most C. jejuni strains with human gangliosides presents safety concerns about the development of Guillain-Barré syndrome. Clinical isolates of C. jejuni that appeared to lack genes for the synthesis of ganglioside mimics were identified by DNA probe analyses. Two clinical isolates from Southeast Asia (strains BH-01-0142 and CG8421) were determined to express the LOS type containing N-acetyl quinovosamine. No ganglioside structures were observed to be present in the LOSs of these strains, and pyrosequence analyses of the genomes of both strains confirmed the absence of genes involved in ganglioside mimicry. The capsule polysaccharide (CPS) of BH-01-0142 was determined to be composed of galactose (Gal), 6-deoxy-ido-heptose, and, in smaller amounts, D-glycero-D-ido-heptose, and the CPS of CG8421 was observed to contain Gal, 6-deoxy-altro-heptose, N-acetyl-glucosamine, and minor amounts of 6-deoxy-3-O-Me-altro-heptose. Both CPSs were shown to carry O-methyl-phosphoramidate. The two genomes contained strain-specific zones, some of which could be traced to a plasmid origin, and both contained a large chromosomal insertion related to the CJEI3 element of C. jejuni RM1221. The genomes of both strains shared a high degree of similarity to each other and, with the exception of the capsule locus of CG8421, to the type strain of the HS3 serotype, TGH9011.

Restoration of flagellar biosynthesis by varied mutational events in Campylobacter jejuni

Both a complex regulatory cascade involving the FlgSR two-component system and phase variation control expression of sigma(54)-dependent flagellar genes in Campylobacter jejuni. In this study, mutational mechanisms influencing production of the FlgS histidine kinase were discovered. Random non-motile, non-flagellated flgS variants were impaired for growth in the chick intestinal tract. Spontaneous revertants restored for flagellar biosynthesis, gene expression, and motility identified by in vivo and in vitro studies had undergone diverse intragenic and extragenic mutational events relative to flgS. Restorative intragenic events included true phase variation, second-site intragenic reversion, and insertion and deletion of short DNA segments within flgS. In vivo-isolated motile revertants possessed an identical, single extragenic mutation to create a partially constitutively active FlgR protein in the absence of FlgS. Considering that FlgR production is also influenced by phase variation, these new findings suggest that the FlgSR two-component system is unique in that each protein is controlled by phase variation and phosphorylation. In addition, this study highlights the mutational activities of C. jejuni and suggests that the bacterium may possess a repertoire of mutational mechanisms to overcome genetic lesions that impair production of virulence and colonization determinants while lacking a normal mismatch repair system.

Host-pathogen interactions in Campylobacter infections: the host perspective

Campylobacter is a major cause of acute bacterial diarrhea in humans worldwide. This study was aimed at summarizing the current understanding of host mechanisms involved in the defense against Campylobacter by evaluating data available from three sources: (i) epidemiological observations, (ii) observations of patients, and (iii) experimental observations including observations of animal models and human volunteer studies. Analysis of available data clearly indicates that an effective immune system is crucial for the host defense against Campylobacter infection. Innate, cell-mediated, and humoral immune responses are induced during Campylobacter infection, but the relative importance of these mechanisms in conferring protective immunity against reinfection is unclear. Frequent exposure to Campylobacter does lead to the induction of short-term protection against disease but most probably not against colonization. Recent progress in the development of more suitable animal models for studying Campylobacter infection has opened up possibilities to study the importance of innate and adaptive immunity during infection and in protection against reinfection. In addition, advances in genomics and proteomics technologies will enable more detailed molecular studies. Such studies combined with better integration of host and pathogen research driven by epidemiological findings may truly advance our understanding of Campylobacter infection in humans.

Influence of growth conditions on diverse polysaccharide production byCampylobacter jejuni

Campylobacter jejuni is the leading bacterial cause of gastroenteritis worldwide. The present study was undertaken to determine the forms of polysaccharide-related compounds (PRCs) produced by C. jejuni and the culture conditions influencing their production. Expression of polysaccharides by C. jejuni was influenced by culture medium composition and growth phase. In addition to the production of lipooligosaccharide and capsular polysaccharide, a previously undescribed polysaccharide, not related to capsular polysaccharide, was shown to occur in C. jejuni in batch liquid and chemostat cultures. Thus, a variety of PRCs are produced by C. jejuni, and this should be considered when growing the bacterium in vitro for pathogenesis studies.

Bacterial populations as perfect gases: genomic integrity and diversification tensions in Helicobacter pylori

Microorganisms that persist in single hosts face particular challenges. Helicobacter pylori, an obligate bacterial parasite of the human stomach, has evolved a lifestyle that features interstrain competition and intraspecies cooperation, both of which involve horizontal gene transfer. Microbial species must maintain genomic integrity, yet H. pylori has evolved a complex nonlinear system for diversification that exists in dynamic tension with the mechanisms for ensuring fidelity. Here, we review these tensions and propose that they create a dynamic pool of genetic variants that is sufficiently genetically diverse to allow H. pylori to occupy all of the potential niches in the stomach.

Campylobacter jejuni colonization of mice with limited enteric flora

We have developed experimental murine Campylobacter infection models which demonstrate efficient establishment and reproducible, high-level colonization. Following oral inoculation, wild-type C3H mice with normal enteric flora were colonized inconsistently and inefficiently by C. jejuni strain 81-176. However, C3H mice with a limited gut flora (LF) were efficiently colonized at high levels (10(8) CFU/g of stool or large intestine tissue) followed by clearance after several weeks. Large intestine tissue showed minimal to mild inflammation at days 7 and 28 postinoculation. In striking contrast, C3H SCID mice with the same limited flora remained persistently colonized at a consistently high level until they were euthanized 8 months postinoculation. Lower gastrointestinal tract tissue from LF-SCID mice showed marked to severe inflammation in the colon and cecum at days 7 and 28 and intense inflammation of the stomach at day 28. These findings indicate that although the innate response alone cannot block colonization persistence, it is sufficient to orchestrate marked gut inflammation. Moreover, the adaptive immune response is critical to mediate C. jejuni clearance from the colonized gut. To validate our LF murine model, we verified that motility and chemotaxis are critical for colonization. Insertion-deletion mutations were generated in motB and fliI, which encode products essential for motility and flagellar assembly, and in the presumptive chemotaxis gene cheA (histidine kinase). All mutants failed to establish colonization in LF mice. Our limited flora murine colonization models serve as tractable, reproducible tools to define host responses to C. jejuni infection and to identify and characterize virulence determinants required for colonization.

A phase-variable mechanism controlling the Campylobacter jejuni FlgR response regulator influences commensalism

Phase variation of genes in bacteria enables phenotypic alteration to modulate interactions within a host as conditions change. To promote commensalism in animals and disease in humans, Campylobacter jejuni produces a flagellar organelle for motility. In addition to tight transcriptional regulation of flagellar genes, C. jejuni also controls flagellar biosynthesis by phase variation. In this study, an unusual phase-variable mechanism controlling production of FlgR, the response regulator of the FlgSR two-component system required for transcription of sigma54-dependent flagellar genes, is identified. Phase variation of FlgR production is due to loss or gain of a nucleotide in homopolymeric adenine or thymine tracts within flgR. This mechanism occurs during commensalism in poultry to alter the colonization capacity of C. jejuni, presumably by influencing the motility phenotype of the bacterium. These findings provide more understanding into the genetic and colonization strategies C. jejuni employs to achieve commensalism in a natural host. Second, due to the richness of the C. jejuni genome in adenine or thymine residues and the apparent lack of the normal set of mismatch repair enzymes, the results from this study may suggest that the C. jejuni genome is more unstable and variable than previously realized. Furthermore, phase variation of flagellar motility by targeting flgR may be a phenomenon specific to C. jejuni that is absent in other Campylobacter species and contribute to reasons why C. jejuni is more frequently found as a commensal organism in poultry and as the cause of disease in humans.

Unique features of a highly pathogenic Campylobacter jejuni strain

Campylobacter jejuni, a major human enteric pathogen, exhibits significant strain-to-strain differences which result in differences in pathogenic potential. C. jejuni 81-176 is a highly virulent strain that exhibits unique pathogenic features and is used by many research laboratories. We have determined the nucleotide sequence of its genome and compared it to the genomes of other sequenced C. jejuni strains. We identified a number of unique genetic features which may confer specific metabolic and pathogenic properties on this strain. We have also identified regions of the C. jejuni genome that are hot spots for the integration of horizontally acquired genetic material. This information should help the understanding of the pathogenesis of C. jejuni and, in particular, the unique features of this highly pathogenic strain.

A recombinant probiotic for treatment and prevention of cholera

BACKGROUND & AIMS

We have developed a therapeutic strategy based on molecular mimicry of host receptors for bacterial toxins on the surface of harmless gut bacteria. In the present study, this has been applied to the development of a recombinant probiotic for treatment and prevention of cholera, caused by Vibrio cholerae.

METHODS

We expressed glycosyltransferase genes from Neisseria gonorrhoeae and Campylobacter jejuni in a harmless Escherichia coli strain, resulting in production of a chimeric lipopolysaccharide terminating in a mimic of the ganglioside GM(1).

RESULTS

The recombinant bacterium was capable of binding cholera toxin, a sine qua non of virulence, with high avidity; when tested with purified cholera toxin, it was capable of adsorbing >5% of its own weight of toxin in vitro. Administration of the GM(1)-expressing probiotic also protected infant mice against challenge with virulent V cholerae, even when treatment was delayed until after establishment of infection. When treatment commenced 1 hour after challenge, 12 of 12 mice given the probiotic survived, compared with only 1 of 12 for control mice (P < .00001).

CONCLUSIONS

Toxin-binding probiotics such as that described here have considerable potential for prophylaxis and treatment of cholera in humans.

Structural and functional divergence of MutS2 from bacterial MutS1 and eukaryotic MSH4-MSH5 homologs

MutS homologs, identified in nearly all bacteria and eukaryotes, include the bacterial proteins MutS1 and MutS2 and the eukaryotic MutS homologs 1 to 7, and they often are involved in recognition and repair of mismatched bases and small insertion/deletions, thereby limiting illegitimate recombination and spontaneous mutation. To explore the relationship of MutS2 to other MutS homologs, we examined conserved protein domains. Fundamental differences in structure between MutS2 and other MutS homologs suggest that MutS1 and MutS2 diverged early during evolution, with all eukaryotic homologs arising from a MutS1 ancestor. Data from MutS1 crystal structures, biochemical results from MutS2 analyses, and our phylogenetic studies suggest that MutS2 has functions distinct from other members of the MutS family. A mutS2 mutant was constructed in Helicobacter pylori, which lacks mutS1 and mismatch repair genes mutL and mutH. We show that MutS2 plays no role in mismatch or recombinational repair or deletion between direct DNA repeats. In contrast, MutS2 plays a significant role in limiting intergenomic recombination across a range of donor DNA tested. This phenotypic analysis is consistent with the phylogenetic and biochemical data suggesting that MutS1 and MutS2 have divergent functions.

The crucial role of Campylobacter jejuni genes in anti-ganglioside antibody induction in Guillain-Barre syndrome

Molecular mimicry of Campylobacter jejuni lipo-oligosaccharides (LOS) with gangliosides in nervous tissue is considered to induce cross-reactive antibodies that lead to Guillain-Barre syndrome (GBS), an acute polyneuropathy. To determine whether specific bacterial genes are crucial for the biosynthesis of ganglioside-like structures and the induction of anti-ganglioside antibodies, we characterized the C. jejuni LOS biosynthesis gene locus in GBS-associated and control strains. We demonstrated that specific types of the LOS biosynthesis gene locus are associated with GBS and with the expression of ganglioside-mimicking structures. Campylobacter knockout mutants of 2 potential GBS marker genes, both involved in LOS sialylation, expressed truncated LOS structures without sialic acid, showed reduced reactivity with GBS patient serum, and failed to induce an anti-ganglioside antibody response in mice. We demonstrate, for the first time, to our knowledge, that specific bacterial genes are crucial for the induction of anti-ganglioside antibodies.

The crucial role of Campylobacter jejuni genes in anti-ganglioside antibody induction in Guillain-Barre syndrome

Molecular mimicry of Campylobacter jejuni lipo-oligosaccharides (LOS) with gangliosides in nervous tissue is considered to induce cross-reactive antibodies that lead to Guillain-Barre syndrome (GBS), an acute polyneuropathy. To determine whether specific bacterial genes are crucial for the biosynthesis of ganglioside-like structures and the induction of anti-ganglioside antibodies, we characterized the C. jejuni LOS biosynthesis gene locus in GBS-associated and control strains. We demonstrated that specific types of the LOS biosynthesis gene locus are associated with GBS and with the expression of ganglioside-mimicking structures. Campylobacter knockout mutants of 2 potential GBS marker genes, both involved in LOS sialylation, expressed truncated LOS structures without sialic acid, showed reduced reactivity with GBS patient serum, and failed to induce an anti-ganglioside antibody response in mice. We demonstrate, for the first time, to our knowledge, that specific bacterial genes are crucial for the induction of anti-ganglioside antibodies.

Bacteria and human autoimmunity: the case of primary biliary cirrhosis

PURPOSE OF REVIEW

Primary biliary cirrhosis is a chronic inflammatory disease of the intrahepatic bile ducts that eventually leads to liver cirrhosis and organ failure, in which several observations suggest an autoimmune origin. Similarly to other autoimmune diseases, microbial mediated molecular mimicry is the most widely studied trigger that may break immunologic tolerance in primary biliary cirrhosis.

RECENT FINDINGS

The hypothesis of a bacterial role in the cause of primary biliary cirrhosis has received recent attention, based on in vitro data and the identification of a unique xenobiotic-metabolizing bacterium that modulates naturally occurring environmental estrogens, namely, Novosphingobium aromaticivorans.

SUMMARY

The evidence indicates that bacteria, through different mechanisms, may precipitate autoimmunity in primary biliary cirrhosis and other autoimmune diseases. These data have several implications.