Frédéric Poly

Pathogenesis of Campylobacter.

Purpose of review Molecular pathogenesis of Campylobacter jejuni has lagged behind that of other enteric pathogens. This review summarizes advances in the biology and pathogenesis of C. jejuni. Recent findings Multiple genome sequences have defined conserved and hypervariable loci in the C. jejuni genome. Interaction of C. jejuni with eukaryotic cells results in numerous signal transduction changes and release of proinflammatory cytokines. In-vivo models based on immune knockout mice have also revealed new information on pathogenesis. Summary New information and new methods are available that should provide important tools to further understand pathogenesis of this elusive pathogen.

Heterogeneity of a Campylobacter jejuni Protein That Is Secreted through the Flagellar Filament

ABSTRACT Cj0859c, or FspA, is a small, acidic protein of Campylobacter jejuni that is expressed by a σ28 promoter. Analysis of the fspA gene in 41 isolates of C. jejuni revealed two overall variants of the predicted protein, FspA1 and FspA2. Secretion of FspA occurs in broth-grown bacteria and requires a minimum flagellar structure. The addition of recombinant FspA2, but not FspA1, to INT407 cells in vitro resulted in a rapid induction of apoptosis. These data define a novel C. jejuni virulence factor, and the observed heterogeneity among fspA alleles suggests alternate virulence potential among different strains.

Genome Sequence of a Clinical Isolate of Campylobacter jejuni from Thailand

ABSTRACT Campylobacter jejuni CG8486, which belongs to the HS4 complex, was isolated from a patient with inflammatory diarrhea in Thailand. This strain caused a diarrheal disease in ferrets comparable to that caused by C. jejuni strain 81-176, but it was much less invasive for epithelial cells in vitro than 81-176. Complete genome sequencing of CG8486 revealed a 1.65-Mb genome that was very similar to the other two published genomes of clinical isolates of C. jejuni, the genomes of 81-176 and NCTC 11168, with a limited number of CG8486-specific genes mapping outside the hypervariable carbohydrate biosynthesis loci. These data suggest that the genes required for induction of inflammatory diarrhea are among the genes shared by CG8486 and 81-176 but that either major changes in the carbohydrate loci and/or more subtle changes in other genes may modulate virulence.

Campylobacter Polysaccharide Capsules: Virulence and Vaccines

Campylobacter jejuni remains a major cause of bacterial diarrhea worldwide and is associated with numerous sequelae, including Guillain Barré Syndrome, inflammatory bowel disease, reactive arthritis, and irritable bowel syndrome. C. jejuni is unusual for an intestinal pathogen in its ability to coat its surface with a polysaccharide capsule (CPS). These capsular polysaccharides vary in sugar composition and linkage, especially those involving heptoses of unusual configuration and O-methyl phosphoramidate linkages. This structural diversity is consistent with CPS being the major serodeterminant of the Penner scheme, of which there are 47 C. jejuni serotypes. Both CPS expression and expression of modifications are subject to phase variation by slip strand mismatch repair. Although capsules are virulence factors for other pathogens, the role of CPS in C. jejuni disease has not been well defined beyond descriptive studies demonstrating a role in serum resistance and for diarrhea in a ferret model of disease. However, perhaps the most compelling evidence for a role in pathogenesis are data that CPS conjugate vaccines protect against diarrheal disease in non-human primates. A CPS conjugate vaccine approach against this pathogen is intriguing, but several questions need to be addressed, including the valency of CPS types required for an effective vaccine. There have been numerous studies of prevalence of CPS serotypes in the developed world, but few studies from developing countries where the disease incidence is higher. The complexity and cost of Penner serotyping has limited its usefulness, and a recently developed multiplex PCR method for determination of capsule type offers the potential of a more rapid and affordable method. Comparative studies have shown a strong correlation of the two methods and studies are beginning to ascertain CPS-type distribution worldwide, as well as examination of correlation of severity of illness with specific CPS types.

The Polysaccharide Capsule of Campylobacter jejuni Modulates the Host Immune Response

ABSTRACT Campylobacter jejuni is a major cause of bacterial diarrheal disease worldwide. The organism is characterized by a diversity of polysaccharide structures, including a polysaccharide capsule. Most C. jejuni capsules are known to be decorated nonstoichiometrically with methyl phosphoramidate (MeOPN). The capsule of C. jejuni 81-176 has been shown to be required for serum resistance, but here we show that an encapsulated mutant lacking the MeOPN modification, an mpnC mutant, was equally as sensitive to serum killing as the nonencapsulated mutant. A nonencapsulated mutant, a kpsM mutant, exhibited significantly reduced colonization compared to that of wild-type 81-176 in a mouse intestinal colonization model, and the mpnC mutant showed an intermediate level of colonization. Both mutants were associated with higher levels of interleukin 17 (IL-17) expression from lamina propria CD4+ cells than from cells from animals infected with 81-176. In addition, reduced levels of Toll-like receptor 4 (TLR4) and TLR2 activation were observed following in vitro stimulation of human reporter cell lines with the kpsM and mpnC mutants compared to those with wild-type 81-176. The data suggest that the capsule polysaccharide of C. jejuni and the MeOPN modification modulate the host immune response.

Discrimination of Major Capsular Types of Campylobacter jejuni by Multiplex PCR

ABSTRACT The polysaccharide capsule (CPS) of Campylobacter jejuni is the major serodeterminant of the Penner serotyping scheme. There are 47 Penner serotypes of C. jejuni, 22 of which fall into complexes of related serotypes. A multiplex PCR method for determination of capsule types of Campylobacter jejuni which is simpler and more affordable than classical Penner typing was developed. Primers specific for each capsule type were designed on the basis of a database of gene sequences from the variable capsule loci of 8 strains of major serotypes sequenced in this study and 10 published sequences of other serotypes. DNA sequence analysis revealed a mosaic nature of the capsule loci, suggesting reassortment of genes by horizontal transfer, and demonstrated a high degree of conservation of genes within Penner complexes. The multiplex PCR can distinguish 17 individual serotypes in two PCRs with sensitivities and specificities ranging from 90 to 100% using 244 strains of known Penner type.

The chemical structure and genetic locus of Campylobacter jejuni CG8486 (serotype HS:4) capsular polysaccharide: the identification of 6-deoxy-D-ido-heptopyranose.

In line with our on-going efforts to create a multivalent anti-Campylobacter jejuni vaccine based on its capsule polysaccharides (CPSs), we report here the chemical structure and the genetic locus of the CPS produced by C. jejuni strain CG8486, which belongs to the serotype HS:4 CPS complex. C. jejuni CG8486 CPS was observed to be composed of approximately 17 disaccharide repeating blocks of 4-substituted N-acetyl-beta-D-glucopyranosamine and 3-substituted 6-deoxy-beta-D-ido-heptopyranose. A small number of 6-deoxy-beta-D-ido-heptopyranose units were observed to carry O-methyl phosphoramidate moieties at the O-2 or O-7 position. The gene content and organization of the CPS locus of C. jejuni CG8486 were comparable to those of C. jejuni strains NCTC 11168 and 81-176, but several CG8486 CPS genes were observed to be more divergent from those present in the CPS loci of NCTC 11168 and 81-176 CPS, which indicated that there are genetic characteristics specific to the C. jejuni HS:4 CPS complex. The efficacy of a glycoconjugate vaccine based on C. jejuni CG8486 CPS is presently being tested in an animal model, the results of which will be presented in future communications.

Lack of Homologous Protection against Campylobacter jejuni CG8421 in a Human Challenge Model

BACKGROUND Campylobacter jejuni is a common cause of diarrhea and is associated with serious postinfectious sequelae. Although symptomatic and asymptomatic infections are recognized, protective immunity is not well understood. Previous data suggests that interferon γ (IFN-γ) may be associated with protection. To better define the clinical and immunologic development of protective immunity to C. jejuni, we assessed the ability of an initial infection to prevent clinical illness after a second experimental infection. METHODS Subjects with no clinical or immunologic evidence of prior infection with C. jejuni received an initial challenge with C. jejuni CG8421 with rechallenge 3 months later. The primary endpoint was campylobacteriosis, as defined by diarrhea and/or systemic signs. Close inpatient monitoring was performed. Serum immunoglobulin A (IgA) and immunoglobulin G (IgG), fecal IgA, IgA antibody-secreting cells (ASCs), and IFN-γ production were evaluated. All subjects were treated with antibiotics and were clinically well at discharge. RESULTS Fifteen subjects underwent a primary infection with C. jejuni CG8421; 14 (93.3%) experienced campylobacteriosis. Eight subjects received the second challenge, and all experienced campylobacteriosis with similar severity. Immune responses after primary infection included serum IgA, IgG, ASC, and IFN-γ production. Responses were less robust after secondary infection. CONCLUSIONS In naive healthy adults, a single infection with CG8421 did not protect against campylobacteriosis. Although protection has been demonstrated with other strains and after continuous environmental exposure, our work highlights the importance of prior immunity, repeated exposures, and strain differences in protective immunity to C. jejuni. CLINICAL TRIALS REGISTRATION NCT01048112.

Recrudescent Campylobacter jejuni Infection in an Immunocompetent Adult following Experimental Infection with a Well-Characterized Organism

ABSTRACT The recrudescence of infection with Campylobacter jejuni after appropriate antibiotic treatment has not been previously reported in an immunocompetent adult. We present the complete clinical, microbiologic, and immunologic evaluation of a closely monitored healthy male with recrudescent C. jejuni infection occurring in the absence of immunodeficiency following experimental infection with a well-characterized strain. After antibiotic treatment, the initial infection was clinically cleared and microbiologically undetectable. Subsequently, two episodes of recrudescence occurred, with no change in in vitro antibiotic sensitivity being detected. The immune responses of the individual were compared to those of other participants in the experimental infection study: innate immune responses, including fecal cytokines and C-reactive protein, were intact; however, measures of Campylobacter-specific adaptive immune responses were absent, including serum antibodies, antibody-secreting cells, and in vitro gamma interferon responses. No primary or secondary immunodeficiency was identified. Recrudescent Campylobacter infections after treatment may be more common than has previously been appreciated. This work adds to our understanding of the human immune response to natural Campylobacter infection and reiterates the importance of pathogen-specific adaptive immune responses to this globally important pathogen.

A capsule conjugate vaccine approach to prevent diarrheal disease caused by Campylobacter jejuni

Campylobacter jejuni is a major cause of diarrheal disease and results in high levels of morbidity and economic loss in both industrialized and developing regions of the world. To date, prior vaccine approaches have failed to confer protection against this enteric pathogen. Key challenges to the development of a practical Campylobacter vaccine for human use include a lack of understanding of Campylobacter pathogenesis and well-defined immune correlates of protection. With the discovery that C. jejuni expresses a capsule polysaccharide associated with virulence, a conjugate vaccine approach is currently being evaluated. Conjugate vaccines have been successfully developed and implemented against other invasive mucosal pathogens including Streptococcus pneumoniae, Neisseria meningitidis,and Hemophilus influenzae. Furthermore, Shigella-based conjugate vaccines based on lipopolysaccharide have shown promising results in field trials. A prototype C. jejuni conjugate vaccine is currently entering human testing.