Sequence polymorphism, predicted secondary structures, and surface-exposed conformational epitopes of Campylobacter major outer membrane protein

Campycins are novel broad-spectrum antibacterials killing Campylobacter jejuni

Pyocins are high molecular weight bacteriocins produced by Pseudomonas aeruginosa that can be retargeted to new bacterial species by exchanging the pyocin tail fibers with bacteriophage receptor binding proteins (RBPs). Here, we develop retargeted pyocins called campycins as new antibacterials to precisely and effectively kill the major foodborne pathogen Campylobacter jejuni. We used two diverse RBPs (H-fibers) encoded by CJIE1 prophages found in the genomes of C. jejuni strains CAMSA2147 and RM1221 to construct campycin 1 and campycin 2, respectively. Campycins 1 and 2 could target all C. jejuni strains tested due to complementary antibacterial spectra. In addition, both campycins led to more than 3 log reductions in C. jejuni counts under microaerobic conditions at 42 °C, whereas the killing efficiency was less efficient under anaerobic conditions at 5 °C. Furthermore, we discovered that both H-fibers used to construct the campycins bind to the essential major outer membrane protein (MOMP) present in all C. jejuni in a strain-specific manner. Protein sequence alignment and structural modeling suggest that the highly variable extracellular loops of MOMP form the binding sites of the diverse H-fibers. Further in silico analyses of 5000 MOMP sequences indicated that the protein falls into three major clades predicted to be targeted by either campycin 1 or campycin 2. Thus, campycins are promising antibacterials against C. jejuni and are expected to broadly target numerous strains of this human pathogen in nature and agriculture. KEY POINTS: • Campycins are engineered R-type pyocins containing H-fibers from C. jejuni prophages • Campycins reduce C. jejuni counts by >3 logs at conditions promoting growth • Campycins bind to the essential outer membrane protein MOMP in a strain-dependent way.

The pathology of natural and experimentally induced Campylobacter jejuni abortion in sheep

We describe here the gross and microscopic lesions in 18 experimentally induced and 120 natural Campylobacter abortions. In natural Campylobacter abortions, gross lesions were reported infrequently; placentitis was recorded in 6% and hepatic lesions in 4% of our field cases. Placentitis was the microscopic lesion identified most consistently in natural abortions (93%) and was often observed in association with abundant bacterial colonies in chorionic villi (54%) and less often with placental vasculitis (13%). In natural abortions, suppurative fetal pneumonia (48%), necrosuppurative hepatitis (16%), and purulent meningitis (7%) were also observed. The better-preserved specimens from experimentally induced abortions were utilized to define placental changes more precisely. Placentitis was identified in all 18 experimentally induced abortions and was observed most consistently in the chorionic villus stroma (100%), often accompanied by suppurative surface exudate (89%). An inflammatory infiltrate was less commonly identified in the cotyledonary hilus (39%) and intercotyledonary placenta (22%). Bacteria were visualized in H&E-stained sections in 89% of placentas from experimentally infected ewes, primarily as well-demarcated bacterial colonies within subtrophoblastic, sinusoidal capillaries (89%), in the cotyledonary villus stroma (89%), and within the cytoplasm of trophoblasts (22%). Transmission electron microscopy and immunohistochemistry confirmed that the vast majority of the well-demarcated bacterial colonies characteristic of Campylobacter abortion were within subtrophoblastic sinusoidal capillaries. The most characteristic microscopic lesions identified in cases of Campylobacter abortion in sheep were placentitis with placental bacterial colonies, placental vasculitis, and fetal pneumonia.

Membrane Proteocomplexome of Campylobacter jejuni Using 2-D Blue Native/SDS-PAGE Combined to Bioinformatics Analysis

Campylobacter is the leading cause of the human bacterial foodborne infections in the developed countries. The perception cues from biotic or abiotic environments by the bacteria are often related to bacterial surface and membrane proteins that mediate the cellular response for the adaptation of Campylobacter jejuni to the environment. These proteins function rarely as a unique entity, they are often organized in functional complexes. In C. jejuni, these complexes are not fully identified and some of them remain unknown. To identify putative functional multi-subunit entities at the membrane subproteome level of C. jejuni, a holistic non a priori method was addressed using two-dimensional blue native/Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) in strain C. jejuni 81-176. Couples of acrylamide gradient/migration-time, membrane detergent concentration and hand-made strips were optimized to obtain reproducible extraction and separation of intact membrane protein complexes (MPCs). The MPCs were subsequently denatured using SDS-PAGE and each spot from each MPCs was identified by mass spectrometry. Altogether, 21 MPCs could be detected including multi homo-oligomeric and multi hetero-oligomeric complexes distributed in both inner and outer membranes. The function, the conservation and the regulation of the MPCs across C. jejuni strains were inspected by functional and genomic comparison analyses. In this study, relatedness between subunits of two efflux pumps, CmeABC and MacABputC was observed. In addition, a consensus sequence CosR-binding box in promoter regions of MacABputC was present in C. jejuni but not in Campylobacter coli. The MPCs identified in C. jejuni 81-176 membrane are involved in protein folding, molecule trafficking, oxidative phosphorylation, membrane structuration, peptidoglycan biosynthesis, motility and chemotaxis, stress signaling, efflux pumps and virulence.

A Homologous Bacterin Protects Sheep against Abortion Induced by a Hypervirulent Campylobacter jejuni Clone

Campylobacter jejuni clone SA has emerged as the predominant cause of ovine abortion outbreaks in the United States (US). Despite the fact that commercial Campylobacter vaccines are available, their efficacy in protecting abortion induced by C. jejuni clone SA is uncertain, and a protective vaccine is needed to control the disease. In this study, an experimental homologous bacterin (made of a clone SA isolate) and two commercial Campylobacter vaccines were evaluated for their protection against C. jejuni clone SA-induced sheep abortion. All vaccines induced high levels of antibodies against C. jejuni clone SA in pregnant ewes, but only the experimental homologous bacterin produced significant protection (80%). Immunoblotting showed that the experimental vaccine elicited more specific antibodies against C. jejuni clone SA. These findings strongly suggest the necessity of developing a homologous vaccine for the control C. jejuni clone SA induced abortion on sheep farms.

Detection and identification of adhesins involved in adhesion of Campylobacter jejuni to chicken skin

Campylobacter jejuni is the leading cause of bacterial food poisoning worldwide. Chickens are considered to be one of the major reservoirs of Campylobacter infection in humans due to colonization of their intestinal tract. When the chickens are slaughtered and processed, the entire skin of the carcass becomes contaminated with campylobacters. We observed that the number of C. jejuni attached to chicken skin was reduced significantly after treatment of the skin with sodium hydroxide followed by washing with PBS, implying that adhesion factors involved in binding to C. jejuni may exist on skin. Such potential binding-related proteins present in alkaline extracts of the skin surface were detected by a two-dimensional overlay assay and identified by liquid chromatography mass spectrometry (LC-MS). Chicken serum albumin (CSA) was identified as a major protein in these alkaline extracts and confirmed by ELISA to bind specifically to C. jejuni. Moreover, using the same approach, flagellar hook protein E (FlgE) and major outer membrane protein (MOMP) in C. jejuni were identified as bacterial adhesins that bound to the CSA. The ability to bind CSA was also confirmed using recombinant FlgE and MOMP of C. jejuni expressed in Escherichia coli. The present findings suggest that adhesins expressed on C. jejuni cells may bind specifically via proteins present on the skin, as well as by physical attachment.

The Rho-Independent Transcription Terminator for the porA Gene Enhances Expression of the Major Outer Membrane Protein and Campylobacter jejuni Virulence in Abortion Induction

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. Its porA gene encodes the major outer membrane protein (MOMP) that is abundantly expressed and has important physiological functions, including a key role in systemic infection and abortion induction in pregnant animals. Despite the importance of porA in C. jejuni pathogenesis, mechanisms modulating its expression levels remain elusive. At the 3' end of the porA transcript, there is a Rho-independent transcription terminator (named T _porA in this study). Whether T _porA affects the expression and function of MOMP remains unknown and is investigated in this study. Green fluorescent protein (GFP) fusion constructs with the porA promoter at the 5' end and an intact T _porA or no T _porA at the 3' end of the gfp coding sequence revealed that both the transcript level of gfp and its fluorescence signals were more than 2-fold higher in the construct with T _porA than in the one without T _porA Real-time quantitative PCR (qRT-PCR) analysis of the porA mRNA and immunoblot detection of MOMP in C. jejuni showed that disruption of T _porA significantly reduced the porA transcript level and the expression of MOMP. An mRNA decay assay demonstrated that disruption of T _porA resulted in a shortened transcript half-life of the upstream gfp or porA gene, indicating that T _porA enhances mRNA stability. In the guinea pig model, the C. jejuni construct with an interrupted T _porA was significantly attenuated in abortion induction. Together, these results indicate that T _porA enhances the expression level of MOMP by stabilizing its mRNA and influences the virulence of C. jejuni.

In vitro spleen cell cytokine responses of adult mice immunized with a recombinant PorA (major outer membrane protein [MOMP]) from Campylobacter jejuni

There is no information on cytokine profiles for use as markers of protection in Campylobacter jejuni infection. To study this, we used outer membrane protein (MOMP [PorA]) as the vaccine for protection and spleen cell cytokines as markers of protection. We cloned and expressed porA from C. jejuni111 and immunized mice by the intraperitoneal route. Subsequently, mice were orally challenged with live C. jejuni 111. The vaccine induced protection as evidenced by reduced fecal excretion of C. jejuni111. Cytokines were measured in vitro after stimulation of spleen cells with MOMP. The levels of pro-inflammatory cytokines, IL-12, TNF-α, IL-17A and IL-17F were similar in control and test mice. The levels of pro-inflammatory cytokines, IL-2 and IFN-γ were higher in control mice than in test mice, and the levels of pro-inflammatory cytokines, IL-8 and IL-1β were higher in test mice than in control mice. Among the two anti-inflammatory cytokines, the levels were similar for IL-10 but higher for IL-4 in test mice than in control mice. Ratios of pro-inflammatory to anti-inflammatory cytokines showed a bias towards an anti-inflammatory response in favor of antibody production reflecting the role of antibodies in immunity. Cytokine production patterns by spleen cells may be used as markers of protection in the mouse model.

Histopathology and Spatial Distribution of Putative Growth Factors in Relation to Bacterial Localization of Campylobacter jejuni Within the Ovine Gallbladder

Campylobacter jejuni is an important zoonotic pathogen that is the leading cause of both human foodborne bacterial gastroenteritis worldwide and ovine abortion in the United States. Previous studies have demonstrated that the gallbladder of ruminants is often positive on culture for Campylobacter sp., suggesting that this environment may serve as a chronic nidus of infection for maintenance of disease within populations. The objective of this study was to determine if previously identified putative growth promoting factors of C. jejuni are present within the gallbladder mucosa of sheep and to evaluate for bacterial co-localization of C. jejuni with these compounds following experimental inoculation. Direct gallbladder inoculation with C. jejuni sheep abortion (SA) clone clinical isolate IA3902 followed by immunohistochemical analysis and scanning electron microscopy allowed for identification of C. jejuni at the gallbladder mucosal surface and within the gallbladder submucosal glands. Histochemistry identified several putative Campylobacter growth promoting factors including neutral and acid mucins as well as L-fucose to be present both on the mucosal surface as well as in the gallbladder submucosal glands. In summary, following experimental inoculation of the ovine gallbladder, C. jejuni IA3902 was identified in direct contact with the gallbladder mucosal surface and deep mucosal glands in the same location as several putative growth promoting factors. This suggests the yet to be tested hypothesis that under natural conditions of infection, the gallbladder submucosal glands have the potential to provide a protected niche for chronic carriage of C. jejuni in animal hosts.

Identification of a nth-Like Gene Encoding an Endonuclease III in Campylobacter jejuni

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. As a microaerobic pathogen, C. jejuni is subjected to DNA damages caused by various stresses such as reactive oxygen species (ROS) and UV radiations. The base excision repair (BER) system plays an important role in preventing mutations associated with oxidative DNA damage, but the system remains poorly characterized in Campylobacter. In this study, a BER homolog encoded by cj0595c (named nth) in C. jejuni was analyzed for endonuclease III activity and for its role in maintaining genomic stability. It was found that inactivation of nth resulted in elevated frequencies of spontaneous fluoroquinolone-resistant (FQ^R) and oxidative stress resistant (OX^R) mutants, compared with the wild-type strain in C. jejuni. Sequencing analysis of the FQ^R and OX^R mutants revealed that the elevated mutation rates were associated with C → T or G → A transition in gyrA (FQ^R mutants) or perR (for OX^R mutants). In an in vitro assay, a purified recombinant C. jejuni Nth protein demonstrated endonuclease III activity that recognized and excised the thymine glycol (Tg) base from a double stranded DNA. These findings indicate that Nth functions as a BER repair enzyme in C. jejuni and is important for the repair of DNA damage, protecting the bacteria from stresses encountered within a host and in the environment.

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.

Genetic Diversity of Campylobacter Jejuni Isolated from the Poultry Food Chain

INTRODUCTION

Campylobacter jejuni is one of the most frequently reported causes of foodborne bacterial enteric disease worldwide. The main source of these microorganisms is contaminated food, especially of poultry origin. There are several molecular methods for differentiation of Campylobacter isolates at the subgenus level, and one of these is porA-typing based on the sequencing of the major outer-membrane protein (MOMP) encoding gene. The aim of the study was to test the molecular relationship of C. jejuni strains isolated at different points along the poultry food chain and assess the population structure of the isolates.

MATERIAL AND METHODS

A total of 451 C. jejuni were used in the study, and a DNA fragment of 630 bp of the MOMP encoding gene was amplified and sequenced.

RESULTS

One hundred and ten sequence types were identified, with 69 (62.7%) unique to the isolates' origin and 30 not present in the database. The most prevalent nucleotide variant 1 was detected in 37 (8.2%) strains. These isolates were identified in all poultry sources tested, especially in faeces (15 isolates) but also in poultry carcasses and meat (11 isolates in each).

CONCLUSION

The porA typing method was highly discriminative for C. jejuni of poultry origin since the Simpson's diversity index (D) achieved a value of 0.876, indicating considerable diversity in the bacterial population tested. The method may be further used for epidemiological investigation purposes.

Intestinal colonization and acute immune response in commercial turkeys following inoculation with Campylobacter jejuni constructs encoding antibiotic-resistance markers

Consumption of contaminated poultry products is one of the main sources of human campylobacteriosis, of which Campylobacter jejuni subsp. jejuni (C. jejuni) is responsible for approximately 90% of the cases. At slaughter, the ceca of commercial chickens and turkeys are the main anatomical site where C. jejuni asymptomatically colonizes. We have previously colonized commercial turkey poults with different isolates of C. jejuni and evaluated different media to best enumerate Campylobacter from intestinal samples, but the host-response is unknown in turkeys. Enumeration of Campylobacter (colony forming units (cfu)/gram of intestinal contents) can be challenging, and can be confounded if animals are colonized with multiple species of Campylobacter. In order to precisely enumerate the C. jejuni isolate used to experimentally colonize turkeys, constructs of C. jejuni (NCTC 11,168) were tagged with different antibiotic resistance markers at the CmeF locus (chloramphenicol (CjCm) or kanamycin (CjK)). We sought to examine the kinetics of intestinal colonization using the antibiotic resistant constructs, and characterize the immune response in cecal tissue of turkeys. In vitro analysis of the tagged antibiotic-resistant constructs demonstrated no changes in motility, morphology, or adherence and invasion of INT-407 cells compared to the parent isolate NCTC 11,168. Two animal experiments were completed to evaluate intestinal colonization by the constructs. In experiment 1, three-week old poults were colonized after oral gavage for 14 days, and CjCm and CjK cfu were recovered from cecal, but not ileal contents. In experiment 2, nine-week old poults were orally inoculated with CjCm, and the abundance of CjCm cfu/g of cecal contents significantly decreased beyond 14 days after inoculation. Significant lesions were detected in CjCm colonized poults at day 2 post-colonization. Using immunohistochemistry, Campylobacter antigen was detected in between cecal villi by day 7 of CjCm colonized poults. Quantitative RT-PCR of CjCm-colonized cecal tissue demonstrated significant down-regulation of IL-1β, IL-10 and IL-13 mRNA, and significant up-regulation of IL-6, IL-8, IL-17 A, IL-22 and IFNγ mRNA on day 2, and for some on day 7 post-colonization. All differentially expressed genes were similar to mock-infected poults by day 14. These data suggest that C. jejuni induced a brief inflammatory response in the cecum of poults that quickly resolved. Results from this study provide valuable insight into host-response and persistent colonization of the turkey cecum. These findings will help to develop and test strategies to promote food safety in commercial turkeys.

A proteome-wide screen of Campylobacter jejuni using protein microarrays identifies novel and conformational antigens

Campylobacter jejuni (C. jejuni) is a foodborne intestinal pathogen and major cause of gastroenteritis worldwide. C. jejuni proteins that are immunogenic have been sought for their potential use in the development of biomarkers, diagnostic assays, or subunit vaccines for humans or livestock. To identify new immunogenic C. jejuni proteins, we used a native protein microarray approach. A protein chip, with over 1400 individually purified GST-tagged C. jejuni proteins, representing over 86% of the proteome, was constructed to screen for antibody titers present in test sera raised against whole C. jejuni cells. Dual detection of GST signals was incorporated as a way of normalizing the variation of protein concentrations contributing to the antibody staining intensities. We detected strong signals to 102 C. jejuni antigens. In addition to antigens recognized by antiserum raised against C. jejuni, parallel experiments were conducted to identify antigens cross-reactive to antiserum raised against various serotypes of E. coli or Salmonella or to healthy human sera. This led to the identification of 34 antigens specifically recognized by the C. jejuni antiserum, only four of which were previously known. The chip approach also allowed identification of conformational antigens. We demonstrate in the case of Cj1621 that antigen signals are lost to denaturing conditions commonly used in other approaches to identify immunogens. Antigens identified in this study include those possessing sequence features indicative of cell surface localization, as well as those that do not. Together, our results indicate that the unbiased chip-based screen can help reveal the full repertoire of host antibodies against microbial proteomes.

CapC, a Novel Autotransporter and Virulence Factor of Campylobacter jejuni

Campylobacter jejuni is recognized as an important causative agent of bacterial gastroenteritis in the developed world. Despite the identification of several factors contributing to infection, characterization of the virulence strategies employed by C. jejuni remains a significant challenge. Bacterial autotransporter proteins are a major class of secretory proteins in Gram-negative bacteria, and notably, many autotransporter proteins contribute to bacterial virulence. The aim of this study was to characterize the C. jejuni 81116 C8J_1278 gene (capC), predicted to encode an autotransporter protein, and examine the contribution of this factor to virulence of C. jejuni The predicted CapC protein has a number of features that are consistent with autotransporters, including the N-terminal signal sequence and the C-terminal β-barrel domain and was determined to localize to the outer membrane. Inactivation of the capC gene in C. jejuni 81116 and C. jejuni M1 resulted in reduced insecticidal activity in Galleria mellonella larvae. Furthermore, C. jejuni capC mutants displayed significantly reduced adherence to and invasion of nonpolarized, partially differentiated Caco-2 and T84 intestinal epithelial cells. Gentamicin treatment showed that the reduced invasion of the capC mutant is primarily caused by reduced adherence to intestinal epithelial cells, not by reduced invasion capability. C. jejuni capC mutants caused reduced interleukin 8 (IL-8) secretion from intestinal epithelial cells and elicited a significantly diminished immune reaction in Galleria larvae, indicating that CapC functions as an immunogen. In conclusion, CapC is a new virulence determinant of C. jejuni that contributes to the integral infection process of adhesion to human intestinal epithelial cells.IMPORTANCECampylobacter jejuni is a major causative agent of human gastroenteritis, making this zoonotic pathogen of significant importance to human and veterinary public health worldwide. The mechanisms by which C. jejuni interacts with intestinal epithelial cells and causes disease are still poorly understood due, in part, to the heterogeneity of C. jejuni infection biology. Given the importance of C. jejuni to public health, the need to characterize novel and existing virulence mechanisms is apparent. The significance of our research is in demonstrating the role of CapC, a novel virulence factor in C. jejuni that contributes to adhesion and invasion of the intestinal epithelium, thereby in part, addressing the dearth of knowledge concerning the factors involved in Campylobacter pathogenesis and the variation observed in the severity of human infection.

Sequence Variation of Rare Outer Membrane Protein β-Barrel Domains in Clinical Strains Provides Insights into the Evolution of Treponema pallidum subsp. pallidum, the Syphilis Spirochete

In recent years, considerable progress has been made in topologically and functionally characterizing integral outer membrane proteins (OMPs) of Treponema pallidum subspecies pallidum, the syphilis spirochete, and identifying its surface-exposed β-barrel domains. Extracellular loops in OMPs of Gram-negative bacteria are known to be highly variable. We examined the sequence diversity of β-barrel-encoding regions of tprC, tprD, and bamA in 31 specimens from Cali, Colombia; San Francisco, California; and the Czech Republic and compared them to allelic variants in the 41 reference genomes in the NCBI database. To establish a phylogenetic framework, we used T. pallidum 0548 (tp0548) genotyping and tp0558 sequences to assign strains to the Nichols or SS14 clades. We found that (i) β-barrels in clinical strains could be grouped according to allelic variants in T. pallidum subsp. pallidum reference genomes; (ii) for all three OMP loci, clinical strains within the Nichols or SS14 clades often harbored β-barrel variants that differed from the Nichols and SS14 reference strains; and (iii) OMP variable regions often reside in predicted extracellular loops containing B-cell epitopes. On the basis of structural models, nonconservative amino acid substitutions in predicted transmembrane β-strands of T. pallidum repeat C (TprC) and TprD2 could give rise to functional differences in their porin channels. OMP profiles of some clinical strains were mosaics of different reference strains and did not correlate with results from enhanced molecular typing. Our observations suggest that human host selection pressures drive T. pallidum subsp. pallidum OMP diversity and that genetic exchange contributes to the evolutionary biology of T. pallidum subsp. pallidum They also set the stage for topology-based analysis of antibody responses to OMPs and help frame strategies for syphilis vaccine development.IMPORTANCE Despite recent progress characterizing outer membrane proteins (OMPs) of Treponema pallidum, little is known about how their surface-exposed, β-barrel-forming domains vary among strains circulating within high-risk populations. In this study, sequences for the β-barrel-encoding regions of three OMP loci, tprC, tprD, and bamA, in T. pallidum subsp. pallidum isolates from a large number of patient specimens from geographically disparate sites were examined. Structural models predict that sequence variation within β-barrel domains occurs predominantly within predicted extracellular loops. Amino acid substitutions in predicted transmembrane strands that could potentially affect porin channel function were also noted. Our findings suggest that selection pressures exerted within human populations drive T. pallidum subsp. pallidum OMP diversity and that recombination at OMP loci contributes to the evolutionary biology of syphilis spirochetes. These results also set the stage for topology-based analysis of antibody responses that promote clearance of T. pallidum subsp. pallidum and frame strategies for vaccine development based upon conserved OMP extracellular loops.

Understanding antibiotic resistance via outer membrane permeability

Collective antibiotic drug resistance is a global threat, especially with respect to Gram-negative bacteria. The low permeability of the bacterial outer cell wall has been identified as a challenging barrier that prevents a sufficient antibiotic effect to be attained at low doses of the antibiotic. The Gram-negative bacterial cell envelope comprises an outer membrane that delimits the periplasm from the exterior milieu. The crucial mechanisms of antibiotic entry via outer membrane includes general diffusion porins (Omps) responsible for hydrophilic antibiotics and lipid-mediated pathway for hydrophobic antibiotics. The protein and lipid arrangements of the outer membrane have had a strong impact on the understanding of bacteria and their resistance to many types of antibiotics. Thus, one of the current challenges is effective interpretation at the molecular basis of the outer membrane permeability. This review attempts to develop a state of knowledge pertinent to Omps and their effective role in solute influx. Moreover, it aims toward further understanding and exploration of prospects to improve our knowledge of physicochemical limitations that direct the translocation of antibiotics via bacterial outer membrane.

A Mutator Phenotype Promoting the Emergence of Spontaneous Oxidative Stress-Resistant Mutants in Campylobacter jejuni

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. As a microaerophilic organism, C. jejuni must be able to defend against oxidative stress encountered both in the host and in the environment. How Campylobacter utilizes a mutation-based mechanism for adaptation to oxidative stress is still unknown. Here we present a previously undescribed phenotypic and genetic mechanism that promotes the emergence of oxidative stress-resistant mutants. Specifically, we showed that a naturally occurring mutator phenotype, resulting from a loss of function mutation in the DNA repair enzyme MutY, increased oxidative stress resistance (OXR) in C. jejuni We further demonstrated that MutY malfunction did not directly contribute to the OXR phenotype but increased the spontaneous mutation rate in the peroxide regulator gene perR, which functions as a repressor for multiple genes involved in oxidative stress resistance. Mutations in PerR resulted in loss of its DNA binding function and derepression of PerR-controlled oxidative stress defense genes, thereby conferring an OXR phenotype and facilitating Campylobacter survival under oxidative stress. These findings reveal a new mechanism that promotes the emergence of spontaneous OXR mutants in bacterial organisms.IMPORTANCE Although a mutator phenotype has been shown to promote antibiotic resistance in many bacterial species, little is known about its contribution to the emergence of OXR mutants. This work describes the link between a mutator phenotype and the enhanced emergence of OXR mutants as well as its underlying mechanism involving DNA repair and mutations in PerR. Since DNA repair systems and PerR are well conserved in many bacterial species, especially in Gram positives, the same mechanism may operate in multiple bacterial species. Additionally, we developed a novel method that allows for rapid quantification of spontaneous OXR mutants in a bacterial population. This method represents a technical innovation and may also be applied to other bacterial species. These findings significantly advance our understanding of bacterial mechanisms for survival under oxidative stress.

Nanobodies targeting conserved epitopes on the major outer membrane protein of Campylobacter as potential tools for control of Campylobacter colonization

Campylobacter infections are among the most prevalent foodborne infections in humans, resulting in a massive disease burden worldwide. Broilers have been identified as the major source of campylobacteriosis and reducing Campylobacter loads in the broiler caeca has been proposed as an effective measure to decrease the number of infections in humans. Failure of current methods to control Campylobacter in broilers stresses the urgency to develop novel mitigation measures. We obtained six nanobodies with a broad specificity, that recognize strains belonging to the two most relevant species, Campylobacter jejuni and Campylobacter coli. The target of the nanobodies was identified as the major outer membrane protein, a porin that contributes to bacterial virulence and viability. Multimerization of the nanobodies led to agglutination of C. jejuni cells, which may affect colonization in the chicken gut. These Campylobacter-specific nanobodies may be useful to develop a strategy for preserving chickens from Campylobacter colonization.

Point mutations in the major outer membrane protein drive hypervirulence of a rapidly expanding clone of Campylobacter jejuni

Infections due to clonal expansion of highly virulent bacterial strains are clear and present threats to human and animal health. Association of genetic changes with disease is now a routine, but identification of causative mutations that enable disease remains difficult. Campylobacter jejuni is an important zoonotic pathogen transmitted to humans mainly via the foodborne route. C. jejuni typically colonizes the gut, but a hypervirulent and rapidly expanding clone of C. jejuni recently emerged, which is able to translocate across the intestinal tract, causing systemic infection and abortion in pregnant animals. The genetic basis responsible for this hypervirulence is unknown. Here, we developed a strategy, termed "directed genome evolution," by using hybridization between abortifacient and nonabortifacient strains followed by selection in an animal disease model and whole-genome sequence analysis. This strategy successfully identified SNPs in porA, encoding the major outer membrane protein, are responsible for the hypervirulence. Defined mutagenesis verified that these mutations were both necessary and sufficient for causing abortion. Furthermore, sequence analysis identified porA as the gene with the top genome-wide signal of adaptive evolution using Fu's Fs, a population genetic metric for recent population size changes, which is consistent with the recent expansion of clone "sheep abortion." These results identify a key virulence factor in Campylobacter and a potential target for the control of this zoonotic pathogen. Furthermore, this study provides general, unbiased experimental and computational approaches that are broadly applicable for efficient elucidation of disease-causing mutations in bacterial pathogens.

Engineering the Campylobacter jejuni N-glycan to create an effective chicken vaccine

Campylobacter jejuni is a predominant cause of human gastroenteritis worldwide. Source-attribution studies indicate that chickens are the main reservoir for infection, thus elimination of C. jejuni from poultry would significantly reduce the burden of human disease. We constructed glycoconjugate vaccines combining the conserved C. jejuni N-glycan with a protein carrier, GlycoTag, or fused to the Escherichia coli lipopolysaccharide-core. Vaccination of chickens with the protein-based or E. coli-displayed glycoconjugate showed up to 10-log reduction in C. jejuni colonization and induced N-glycan-specific IgY responses. Moreover, the live E. coli vaccine was cleared prior to C. jejuni challenge and no selection for resistant campylobacter variants was observed. Analyses of the chicken gut communities revealed that the live vaccine did not alter the composition or complexity of the microbiome, thus representing an effective and low-cost strategy to reduce C. jejuni in chickens and its subsequent entry into the food chain.

Immunization with a Double-Mutant (R192G/L211A) of the Heat-Labile Enterotoxin of Escherichia coli Offers Partial Protection against Campylobacter jejuni in an Adult Mouse Intestinal Colonization Model

We have previously shown that antibodies to cholera toxin (CT) reacted with the major outer membrane proteins (MOMPs) from Campylobacter jejuni strains on Western blot. Further, oral immunization with CT significantly protected against challenge with C. jejuni in an adult mouse colonization model of infection. CT and the heat-labile enterotoxin (LT) of enterotoxigenic Escherichia coli are structurally and functionally related. LT and its mutants including the double-mutant LT (R192G/L211A) (dmLT), are powerful mucosal adjuvants. Unlike LT which is reactogenic, dmLT has been shown to be safe for human use. In the current study, we determined whether rabbit anti-dmLT antibodies reacted with MOMPs from C. jejuni strains and whether immunization with dmLT would afford protection against C. jejuni. On Western blot, the MOMPs from C. jejuni 48 (Penner serotype O:19), C. jejuni 75 (O:3) and C. jejuni 111 (O:1,44) were probed with rabbit antibodies to dmLT or LT-E112K (a non-toxic LT mutant), which showed a lack of reaction. Adult BALB/c mice were orally immunized with dmLT and orally challenged with C. jejuni 48 or 111. Protection from colonization with the challenge bacteria was studied by enumerating Campylobacter colonies in feces daily for 9 days. Vaccination produced robust serum and stool antibody responses to dmLT and no antibody responses to C. jejuni MOMP. Vaccinated mice showed reduced colonization and excretion of both challenge strains compared to control mice. However, the differences were not statistically significant. The protective efficacy of the dmLT vaccine varied from 9.1% to 54.5%. The lack of cross-reaction between the MOMP and dmLT suggests that protection is not mediated by cross-reacting antibodies, but may be due to activation of innate immunity. As dmLT is safe for humans, it could be incorporated into a C. jejuni vaccine to enhance its efficacy.

Helicobacter pullorum isolated from fresh chicken meat: antibiotic resistance and genomic traits of an emerging foodborne pathogen

Meat and meat products are important sources of human intestinal infections. We report the isolation of Helicobacter pullorum strains from chicken meat. Bacteria were isolated from 4 of the 17 analyzed fresh chicken meat samples, using a membrane filter method. MIC determination revealed that the four strains showed acquired resistance to ciprofloxacin; one was also resistant to erythromycin, and another one was resistant to tetracycline. Whole-genome sequencing of the four strains and comparative genomics revealed important genetic traits within the H. pullorum species, such as 18 highly polymorphic genes (including a putative new cytotoxin gene), plasmids, prophages, and a complete type VI secretion system (T6SS). The T6SS was found in three out of the four isolates, suggesting that it may play a role in H. pullorum pathogenicity and diversity. This study suggests that the emerging pathogen H. pullorum can be transmitted to humans by chicken meat consumption/contact and constitutes an important contribution toward a better knowledge of the genetic diversity within the H. pullorum species. In addition, some genetic traits found in the four strains provide relevant clues to how this species may promote adaptation and virulence.

A novel O-linked glycan modulates Campylobacter jejuni major outer membrane protein-mediated adhesion to human histo-blood group antigens and chicken colonization

Campylobacter jejuni is an important cause of human foodborne gastroenteritis; strategies to prevent infection are hampered by a poor understanding of the complex interactions between host and pathogen. Previous work showed that C. jejuni could bind human histo-blood group antigens (BgAgs) in vitro and that BgAgs could inhibit the binding of C. jejuni to human intestinal mucosa ex vivo. Here, the major flagella subunit protein (FlaA) and the major outer membrane protein (MOMP) were identified as BgAg-binding adhesins in C. jejuni NCTC11168. Significantly, the MOMP was shown to be O-glycosylated at Thr²⁶⁸; previously only flagellin proteins were known to be O-glycosylated in C. jejuni. Substitution of MOMP Thr²⁶⁸ led to significantly reduced binding to BgAgs. The O-glycan moiety was characterized as Gal(β1–3)-GalNAc(β1–4)-GalNAc(β1–4)-GalNAcα1-Thr²⁶⁸; modelling suggested that O-glycosylation has a notable effect on the conformation of MOMP and this modulates BgAg-binding capacity. Glycosylation of MOMP at Thr²⁶⁸ promoted cell-to-cell binding, biofilm formation and adhesion to Caco-2 cells, and was required for the optimal colonization of chickens by C. jejuni, confirming the significance of this O-glycosylation in pathogenesis.

Comprehensive proteomic profiling of outer membrane vesicles from Campylobacter jejuni

Gram-negative bacteria constitutively release outer membrane vesicles (OMVs) during cell growth that play significant roles in bacterial survival, virulence and pathogenesis. In this study, comprehensive proteomic analysis of OMVs from a human gastrointestinal pathogen Campylobacter jejuni NCTC11168 was performed using high-resolution mass spectrometry. The OMVs of C. jejuni NCTC11168 were isolated from culture supernatants then characterized using electron microscopy and dynamic light scattering revealing spherical OMVs of an average diameter of 50nm. We then identified 134 vesicular proteins using high-resolution LTQ-Orbitrap mass spectrometry. Subsequent functional analysis of the genes revealed the relationships of the vesicular proteins. Furthermore, known N-glycoproteins were identified from the list of the vesicular proteome, implying the potential role of the OMVs as a delivery means for biologically relevant bacterial glycoproteins. These results enabled us to elucidate the overall proteome profile of pathogenic bacterium C. jejuni and to speculate on the function of OMVs in bacterial infections and communication.

BIOLOGICAL SIGNIFICANCE

This work demonstrates the importance of understanding vesicular proteomes from a human pathogen Campylobacter jejuni. From the secreted outer membrane vesicles (OMVs) of C. jejuni NCTC11168, we found a variety of virulence factors and essential proteins for bacterial survival. Bioinformatics analysis of these proteins predicted functional enrichment and localization. The most highly enriched were redox enzymes, which are considered to be essential for survival in oxygen-limiting environments and are predicted to be on the twin-arginine translocation (Tat) pathway suggesting a role for this pathway in the biogenesis of OMVs. This study additionally implicates a biological role for N-linked glycoproteins in OMVs. These approaches allow for a better understanding of the physiology of this important human pathogen.

Pro-inflammatory cytokines can act as intracellular modulators of commensal bacterial virulence

Interactions between commensal pathogens and hosts are critical for disease development but the underlying mechanisms for switching between the commensal and virulent states are unknown. We show that the human pathogen Neisseria meningitidis, the leading cause of pyogenic meningitis, can modulate gene expression via uptake of host pro-inflammatory cytokines leading to increased virulence. This uptake is mediated by type IV pili (Tfp) and reliant on the PilT ATPase activity. Two Tfp subunits, PilE and PilQ, are identified as the ligands for TNF-α and IL-8 in a glycan-dependent manner, and their deletion results in decreased virulence and increased survival in a mouse model. We propose a novel mechanism by which pathogens use the twitching motility mode of the Tfp machinery for sensing and importing host elicitors, aligning with the inflamed environment and switching to the virulent state.

Evaluation of nanoparticle-encapsulated outer membrane proteins for the control of Campylobacter jejuni colonization in chickens

Numerous vaccination strategies have been evaluated to develop effective vaccines against Campylobacter jejuni colonization in poultry but with limited success. The following experiments were conducted to investigate the effect of biodegradable and biocompatible poly (lactide-co-glycolide) nanoparticle (NP) encapsulated outer membrane proteins (OMP) of C. jejuni. Chickens were vaccinated with different routes [subcutaneous (s/c) or oral] and doses (25, 125, or 250 µg) of candidate nanoparticle vaccine with appropriate control groups. Serum and cloacal fecal samples were taken at regular intervals of time, and the birds were euthanized 7 d postchallenge with C. jejuni. The results were interpreted based on anti-OMP immunoglobulin response in chicken and intestinal colonization of C. jejuni. The C. jejuni colonization in cecal and cloacal contents at 7 d postchallenge was below the detection limit in the s/c vaccinated groups, but the other groups demonstrated varying degrees of colonization. The serum IgA was higher in the group vaccinated s/c with OMP only compared with the rest of the groups. The serum- and fecal-IgY titers were consistently higher in the s/c vaccinated groups (with or without NP) than the rest of the groups. Elevated levels of OMP specific serum antibodies correlated with below the limit of detection levels of Campylobacter colonization in broiler chickens receiving 125 μg of OMP alone and the OMP+NP vaccine s/c. In conclusion, the s/c route of vaccination with or without NP encapsulated OMP of C. jejuni may serve as a candidate vaccine for control of C. jejuni colonization in chickens.

Oral immunization with cholera toxin provides protection against Campylobacter jejuni in an adult mouse intestinal colonization model

Immunity to Campylobacter jejuni, a major diarrheal pathogen, is largely Penner serotype specific. For broad protection, a vaccine should be based on a common antigen(s) present in all strains. In our previous study (M. J. Albert, S. Haridas, D. Steer, G. S. Dhaunsi, A. I. Smith, and B. Adler, Infect. Immun. 75:3070–3073, 2007), we demonstrated that antibody to cholera toxin (CT) cross-reacted with the major outer membrane proteins (MOMPs) of all Campylobacter jejuni strains tested. In the current study, we investigated whether immunization with CT protects against intestinal colonization by C. jejuni in an adult mouse model and whether the nontoxic subunit of CT (CT-B) is the portion mediating cross-reaction. Mice were orally immunized with CT and later challenged with C. jejuni strains (48, 75, and 111) of different serotypes. Control animals were immunized with phosphate-buffered saline. Fecal shedding of challenge organisms was studied daily for 9 days. Serum and fecal antibody responses were studied by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. The cross-reactivity of rabbit CT-B antibody to MOMP was studied by immunoblotting. The reactivity of 21 overlapping 30-mer oligopeptides (based on MOMP’s sequence) against rabbit CT antibody was tested by ELISA. Test animals produced antibodies to CT and MMP in serum and feces and showed resistance to colonization, the vaccine efficacies being 49% (for strain 48), 37% (for strain 75), and 34% (for strain 111) (P, ≤0.05 to ≤0.001). One peptide corresponding to a variable region of MOMP showed significant reactivity. CT-B antibody cross-reacted with MOMP. Since CT-B is a component of oral cholera vaccines, it might be possible to control C. jejuni diarrhea with these vaccines.

Campylobacter jejuni is a major cause of diarrhea worldwide. Patients who recover from C. jejuni diarrhea develop immunity to the infecting serotype and remain susceptible to infection with other serotypes. A vaccine based on a common protective antigen(s) present in all C. jejuni serotypes is expected to provide broad protection. In our previous study, we showed that antibody to cholera toxin (CT) reacted with the major outer membrane proteins (MOMPs) from different strains of C. jejuni. We assumed that the B subunit of the toxin (CT-B), which is nontoxic and a component of licensed oral cholera vaccines, might be the component that cross-reacts with MOMP. In the current study, we showed that orally immunizing mice with CT protected them against colonization upon challenge with different serotypes of C. jejuni. We also showed that CT-B is the component mediating cross-reaction. Therefore, it might be possible to use cholera vaccines to prevent C. jejuni diarrhea. This could result in significant savings in vaccine development and treatment of the disease.

Using major outer membrane protein typing as an epidemiological tool to investigate outbreaks caused by milk-borne Campylobacter jejuni isolates in California

We describe using major outer membrane protein (MOMP) typing as a screen to compare the Campylobacter jejuni porA gene sequences of clinical outbreak strains from human stool with the porA sequences of dairy farm strains isolated during two milk-borne campylobacteriosis outbreak investigations in California. The genetic relatedness of clinical and environmental strains with identical or closely related porA sequences was confirmed by multilocus sequence typing and pulsed-field gel electrophoresis analysis. The first outbreak involved 1,644 C. jejuni infections at 11 state correctional facilities and was associated with consumption of pasteurized milk supplied by an on-site dairy (dairy A) at a prison in the central valley. The second outbreak involved eight confirmed and three suspect C. jejuni cases linked to consumption of commercial raw milk and raw chocolate colostrum at another central valley dairy (dairy B). Both dairies bottled fluid milk on the farm and distributed the finished product to off-site locations. Altogether, C. jejuni was isolated from 7 of 15 (46.7%) bovine fecal, 12 of 20 (60%) flush alley water, and 1 of 20 (5%) lagoon samples collected on dairy A. At dairy B, C. jejuni was cultured from 9 of 26 (34.6%) bovine fecal samples. Environmental strains indistinguishable from the clinical outbreak strains were found in five flush alley water samples (dairy A) and four bovine fecal samples (dairy B). The findings demonstrate that MOMP typing is a useful tool to triage environmental isolates prior to conducting more labor-intensive molecular typing methods.

Estimating the relative roles of recombination and point mutation in the generation of single locus variants in Campylobacter jejuni and Campylobacter coli

Single locus variants (SLVs) are bacterial sequence types that differ at only one of the seven canonical multilocus sequence typing (MLST) loci. Estimating the relative roles of recombination and point mutation in the generation of new alleles that lead to SLVs is helpful in understanding how organisms evolve. The relative rates of recombination and mutation for Campylobacter jejuni and Campylobacter coli were estimated at seven different housekeeping loci from publically available MLST data. The probability of recombination generating a new allele that leads to an SLV is estimated to be roughly seven times more than that of mutation for C. jejuni, but for C. coli recombination and mutation were estimated to have a similar contribution to the generation of SLVs. The majority of nucleotide differences (98 % for C. jejuni and 85 % for C. coli) between strains that make up an SLV are attributable to recombination. These estimates are much larger than estimates of the relative rate of recombination to mutation calculated from more distantly related isolates using MLST data. One explanation for this is that purifying selection plays an important role in the evolution of Campylobacter. A simulation study was performed to test the performance of our method under a range of biologically realistic parameters. We found that our method performed well when the recombination tract length was longer than 3 kb. For situations in which recombination may occur with shorter tract lengths, our estimates are likely to be an underestimate of the ratio of recombination to mutation, and of the importance of recombination for creating diversity in closely related isolates. A parametric bootstrap method was applied to calculate the uncertainty of these estimates.

Molecular mechanisms and biological role of Campylobacter jejuni attachment to host cells

Adhesion to host cells is an important step in pathogenesis of Campylobacter jejuni, which is the most prevalent bacterial cause of human gastroenteritis worldwide. In contrast to other bacteria such as E. coli and Salmonella, adherence of C. jejuni is not mediated by fimbria or pili. A number of C. jejuni adhesion-related factors have been described. However, the results obtained by different researchers in different laboratories are often contradictory and inconclusive, with only some of the factors described being confirmed as true adhesins. In this review, we present the current state of studies on the mechanisms of attachment of C. jejuni to host cells.

Induction of immune responses by purified outer membrane protein complexes from Neisseria meningitidis

A broad-spectrum vaccine against disease caused by serogroup B of Neisseria meningitidis is still a challenge due to antigenic variability. In the present study outer membrane protein complexes and their components were analysed using non-denaturing 2D electrophoresis and identified using LC/MS-MS and MALDI-TOF. Outer membrane protein complexes were purified from both the wild-type strain H44/76 and their knock-out mutants lacking PorA, PorB, RmpM or FetA. The immune responses elicited by the whole outer membrane vesicles (OMV) and the purified complexes were analysed for bactericidal activity, antibody surface binding, antibody-mediated C3b/iC3b deposition, membrane attack complex (MAC) deposition and induction of opsonophagocytosis, both on the homologous and several heterologous strains. The main antigenic complexes found were homomeric, formed by the 60 kDa chaperonin (MSP63) or PorB, or heteromeric, formed by different combinations of PorA, PorB and/or RmpM. The lack of some of these proteins in the OMVs from the knock-out mutants did not affect significantly the immune responses analysed except MAC, which was significantly reduced in the anti-PorA- and anti-PorB- sera, and bactericidal activity, which was absent in the anti-PorA- serum. The sera against purified native complexes showed variable activities against the homologous strain, with greatest responses observed for anti-chaperonin and anti-PorA/PorB/RmpM sera. When tested against heterologous strains, the only anti-complex serum showing consistent responses was that against the 60 kDa chaperonin. The comparison of the responses elicited by the different sera suggests an important role of conformational epitopes, present only in native complexes, in the induction of more effective responses against N. meningitidis.

Evaluation of Salmonella-vectored Campylobacter peptide epitopes for reduction of Campylobacter jejuni in broiler chickens

Campylobacter is a leading cause of bacterial gastroenteritis in humans and is often linked to contaminated poultry products. Live Salmonella vectors expressing three linear peptide epitopes from Campylobacter proteins Cj0113 (Omp18/CjaD), Cj0982c (CjaA), and Cj0420 (ACE393) were administered to chicks by oral gavage on the day of hatch, and the chicks were challenged with Campylobacter jejuni on day 21. All three candidate vaccines produced consistent humoral immune responses with high levels of serum IgG and mucosal secretory IgA (sIgA), with the best response from the Cj0113 peptide-expressing vector. Campylobacter challenge following vaccination of three candidate vaccine groups decreased Campylobacter recovery from the ileum compared to that for controls on day 32. The Cj0113 peptide-expressing vector reduced Campylobacter to below detectable levels. The Salmonella-vectored Cj0113 subunit vaccine appears to be an excellent candidate for further evaluation as a tool for the reduction of Campylobacter in poultry for improved food safety.

Recombinant PorA, the major outer membrane protein of Campylobacter jejuni, provides heterologous protection in an adult mouse intestinal colonization model

Immunity against Campylobacter jejuni, a major food-borne pathogen causing diarrhea, is largely serotype specific. The major outer membrane protein (MOMP) of C. jejuni, PorA, is a common antigen with the potential to provide broad protection. Adult BALB/c mice were orally immunized with a recombinant glutathione S-transferase (GST) fused to PorA prepared from Campylobacter jejuni C31 (O:6,7) (GST-PorA) combined with a modified heat-labile enterotoxin of Escherichia coli as an adjuvant and later orally challenged with C31 strain or three heterologous strains: 48 (O:19), 75 (O:3), and 111 (O:1,44). Protection from colonization with the challenge organism was studied by fecal screening daily for 9 days. Serum and intestinal lavage fluid antibodies against the vaccine and Sarkosyl-purified MOMP from C31 were measured by using an enzyme-linked immunosorbent assay. The vaccine produced robust antibody responses against both antigens in serum and secretion. Since strain C31 was a poor colonizer, homologous protection could not be studied. The protective efficacies of heterologous strains were 43% (for strain 48, P < 0.001), 29% (for strain 75, P < 0.005), and 42% (for strain 111, P < 0.001) for the 9-day period compared to control mice given phosphate-buffered saline. Thus, PorA provided appreciable protection against colonization with heterologous serotypes.

Proteomic analysis of Neorickettsia sennetsu surface-exposed proteins and porin activity of the major surface protein P51

Neorickettsia sennetsu is an obligate intracellular bacterium of monocytes and macrophages and is the etiologic agent of human Sennetsu neorickettsiosis. Neorickettsia proteins expressed in mammalian host cells, including the surface proteins of Neorickettsia spp., have not been defined. In this paper, we isolated surface-exposed proteins from N. sennetsu by biotin surface labeling followed by streptavidin-affinity chromatography. Forty-two of the total of 936 (4.5%) N. sennetsu open reading frames (ORFs) were detected by liquid chromatography-tandem mass spectrometry (LC/MS/MS), including six hypothetical proteins. Among the major proteins identified were the two major β-barrel proteins: the 51-kDa antigen (P51) and Neorickettsia surface protein 3 (Nsp3). Immunofluorescence labeling not only confirmed surface exposure of these proteins but also showed rosary-like circumferential labeling with anti-P51 for the majority of bacteria and polar to diffuse punctate labeling with anti-Nsp3 for a minority of bacteria. We found that the isolated outer membrane of N. sennetsu had porin activity, as measured by a proteoliposome swelling assay. This activity allowed the diffusion of L-glutamine, the monosaccharides arabinose and glucose, and the tetrasaccharide stachyose, which could be inhibited with anti-P51 antibody. We purified native P51 and Nsp3 under nondenaturing conditions. When reconstituted into proteoliposomes, purified P51, but not Nsp3, exhibited prominent porin activity. This the first proteomic study of a Neorickettsia sp. showing new sets of proteins evolved as major surface proteins for Neorickettsia and the first identification of a porin for the genus Neorickettsia.

Development and Evaluation of CmeC Subunit Vaccine against Campylobacter jejuni

Campylobacter jejuni is the leading bacterial cause of human enteritis in many industrialized countries. There is no commercial vaccine against C. jejuni available to date. CmeC is an essential outer membrane component of CmeABC multidrug efflux pump that plays a critical role in antibiotic resistance and in vivo colonization of C. jejuni. CmeC is prevalent in C. jejuni strains and is dramatically induced and immunogenic in vivo. In this study, we analyzed CmeC sequence homology, examined in vitro immune protection of CmeC peptide antibodies, and produced full-length recombinant CmeC (rCmeC) for evaluating immunogenicity and protective efficacy of the CmeC subunit vaccine against C. jejuni using chicken model system. Amino acid sequences of CmeC from 24 diverse C. jejuni strains were determined and subjected to alignment, which revealed that CmeC is highly conserved in C. jejuni with a identity ranging from 97.3% to 100%. CmeC peptide antibodies inhibited the function of CmeABC efflux pump and enhanced susceptibility of C. jejuni to bile salts, the natural antimicrobial present in the intestine. Two full-length rCmeC proteins with N- or C-terminal His tag were produced in E. coli; the N-terminal His-tagged rCmeC with high purity and yield was obtained by single step affinity purification. The purified rCmeC was used in two vaccination trials using a chicken model of C. jejuni infection. Stimulation of CmeC-specific serum IgG responses via oral vaccination required immunization with higher doses of rCmeC (200μg) together with 70μg of mucosal adjuvant mLT (modified E. coli heat-labile enterotoxin). Subcutaneous vaccination of chickens with rCmeC remarkably stimulated both serum IgG and IgA responses. However, CmeC-specific intestinal secretory IgA response was not significantly stimulated regardless of vaccination regimen and the rCmeC vaccination did not confer protection against C. jejuni infection. Together, these findings provide further compelling evidence that CmeC is a promising subunit vaccine candidate against C. jejuni infection. However, the CmeC vaccination regimen should be optimized to enhance CmeC-specific mucosal immune response in for protection against C. jejuni.

Novel approaches for Campylobacter control in poultry

The Gram-negative bacterium Campylobacter is the most common bacterial cause of human gastroenteritis in the United States and many industrialized countries. Poultry, particularly chickens, is considered a major source of human campylobacteriosis. Thus, on-farm control of Campylobacter in poultry would reduce the risk of human exposure to this pathogen and have a significant impact on food safety and public health. To date, three general strategies have been proposed to control Campylobacter in poultry at the farm level: (1) reduction of environmental exposure (biosecurity measures), (2) an increase in poultry's host resistance to reduce Campylobacter carriage in the gut (e.g., competitive exclusion, vaccination, and host genetics selection), and (3) the use of antimicrobial alternatives to reduce and even eliminate Campylobacter from colonized chickens (e.g., bacteriophage therapy and bacteriocin treatment). Except for biosecurity measures, the other intervention approaches are currently not commercially available and are still under development. This review is focused on two promising strategies--vaccination and bacteriocin treatment. In particular, we extensively review recent research aimed at discovering and characterizing potent anti-Campylobacter bacteriocins to reduce Campylobacter load at the primary production level in poultry.

Pathogenicity of an emergent, ovine abortifacient Campylobacter jejuni clone orally inoculated into pregnant guinea pigs

OBJECTIVE

To compare pathogenicity of an emergent abortifacient Campylobacter jejuni (IA 3902) with that of reference strains after oral inoculation in pregnant guinea pigs.

ANIMALS

58 pregnant guinea pigs.

PROCEDURES

12 animals were challenged IP with C jejuni IA 3902 along with 5 sham-inoculated control animals to confirm abortifacient potential. Once pathogenicity was confirmed, challenge via oral inoculation was performed whereby 12 guinea pigs received IA 3902, 12 received C jejuni isolated from ovine feces (OF48), 12 received a fully sequenced human C jejuni isolate (NCTC 11168), and 5 were sham-inoculated control animals. After abortions, guinea pigs were euthanized; samples were collected for microbial culture, histologic examination, and immunohistochemical analysis.

RESULTS

C jejuni IA 3902 induced abortion in all 12 animals following IP inoculation and 6 of 10 animals challenged orally. All 3 isolates colonized the intestines after oral inoculation, but only IA 3902 induced abortion. Evidence of infection existed for both IA 3902 and NCTC 11168; however, C jejuni was only recovered from fetoplacental units of animals inoculated with IA 3902. Immunohistochemical analysis localized C jejuni IA 3902 infection to subplacental trophoblasts, perivascular tissues, and phagocytes in the placental transitional zone.

CONCLUSIONS AND CLINICAL RELEVANCE

This study revealed that C jejuni IA 3902 was a unique, highly abortifacient strain with the ability to colonize the intestines, induce systemic infection, and cause abortion because of its affinity for the fetoplacental unit. Guinea pigs could be effectively used in the study of septic abortion after oral inoculation with this Campylobacter strain.

Genetic diversity and stability of the porA allele as a genetic marker in human Campylobacter infection

The major outer-membrane protein (MOMP) of Campylobacter jejuni and Campylobacter coli, encoded by the porA gene, is extremely genetically diverse. Conformational MOMP epitopes are important in host immunity, and variation in surface-exposed regions probably occurs as a result of positive immune selection during infection. porA diversity has been exploited in genotyping studies using highly discriminatory nucleotide sequences to identify potentially epidemiologically linked cases of human campylobacteriosis. To understand the overall nature and extent of porA diversity and stability in C. jejuni and C. coli we investigated sequences in isolates (n=584) obtained from a defined human population (approx. 600 000) over a defined time period (1 year). A total of 196 distinct porA variants were identified. Regions encoding putative extracellular loops were the most variable in both nucleotide sequence and length. Phylogenetic analysis identified three porA allele clusters that originated in (i) predominantly C. jejuni and a few C. coli, (ii) solely C. jejuni or (iii) predominantly C. coli and a few C. jejuni. The stability of porA within an individual human host was investigated using isolates cultured longitudinally from 64 sporadic cases, 27 of which had prolonged infection lasting between 5 and 98 days (the remainder having illness of normal duration, 0–4 days), and 20 cases from family outbreaks. Evidence of mutation was detected in two patients with prolonged illness. Despite demonstrable positive immune selection in these two unusual cases, the persistence of numerous variants within the population indicated that the porA allele is a valuable tool for use in extended typing schemes.

Molecular, antigenic, and functional characteristics of ferric enterobactin receptor CfrA in Campylobacter jejuni

The ferric enterobactin receptor CfrA not only is responsible for high-affinity iron acquisition in Campylobacter jejuni but also is essential for C. jejuni colonization in animal intestines. In this study, we determined the feasibility of targeting the iron-regulated outer membrane protein CfrA for immune protection against Campylobacter colonization. Alignment of complete CfrA sequences from 15 Campylobacter isolates showed that the levels of amino acid identity for CfrA range from 89% to 98%. Immunoblotting analysis using CfrA-specific antibodies demonstrated that CfrA was dramatically induced under iron-restricted conditions and was widespread and produced in 32 Campylobacter primary strains from various sources and from geographically diverse areas. The immunoblotting survey results were highly correlated with the results of an enterobactin growth promotion assay and a PCR analysis using cfrA-specific primers. Inactivation of the cfrA gene also impaired norepinephrine-mediated growth promotion, suggesting that CfrA is required for C. jejuni to sense intestinal stress hormones during colonization. Complementation of the cfrA mutant with a wild-type cfrA allele in trans fully restored the production and function of CfrA. A growth assay using purified anti-CfrA immunoglobulin G demonstrated that specific CfrA antibodies could block the function of CfrA, which diminished ferric enterobactin-mediated growth promotion under iron-restricted conditions. The inhibitory effect of CfrA antibodies was dose dependent. Immunoblotting analysis also indicated that CfrA was expressed and immunogenic in chickens experimentally infected with C. jejuni. Amino acid substitution mutagenesis demonstrated that R327, a basic amino acid that is highly conserved in CfrA, plays a critical role in ferric enterobactin acquisition in C. jejuni. Together, these findings strongly suggest that CfrA is a promising vaccine candidate for preventing and controlling Campylobacter infection in humans and animal reservoirs.

Systematic identification of genetic loci required for polymyxin resistance in Campylobacter jejuni using an efficient in vivo transposon mutagenesis system

The aim of this study was to identify genetic loci required for polymyxin (PM) resistance in Campylobacter jejuni using an efficient in vivo random mutagenesis system. PM has been widely used as a model peptide to examine mechanisms of bacterial resistance to antimicrobial peptides (AMPs), the major effectors of host innate immunity and also candidates for a new generation of antibiotics. In this study, a commercially available transposon mutagenesis approach (EZ-Tn5 <KAN-2> Transposome; Epicentre, Madison, WI) was evaluated and used to systematically identify Campylobacter mutants with increased susceptibility to PM. This simple, yet efficient, transposon mutagenesis approach identified 12 mutants representing seven different genes of C. jejuni 81-176 involved in acquired PM resistance. Backcrossing of the transposon mutations into the parent strain confirmed that the PM-sensitive phenotype in each mutant was linked to the gene with a specific transposon insertion. The genes are identified as being involved in the synthesis of cell-surface carbohydrates, modification of intracellular targets, signal transduction, and modulation of transmembrane potential. The mutant with the highest susceptibility to PM contains a transposon insertion in a putative galU gene that is essential for production of uridine diphosphate glucose (UDP)-glucose, a precursor required for lipooligosaccharide (LOS) synthesis. LOS analysis by tricine SDSPAGE showed significant truncation of the LOS core structure in the galU mutant. Susceptibility assays also indicated that GalU contributed C. jejuni resistance to some natural AMPs. Complementation of the galU mutant in trans fully restored LOS synthesis and resistance to the levels of the parent strain. Together, these results define seven C. jejuni genetic loci that will be useful for characterizing the molecular basis of Campylobacter resistance to PM and natural AMPs, and also highlight the usefulness of the in vivo mutagenesis approach for systematic characterization of functionally important Campylobacter genes.

Evaluation of procedures for outer membrane isolation from Campylobacter jejuni

Although infection with Campylobacter jejuni is one of the leading causes of gastroenteritis worldwide, relatively little is known about the factors that are required to elicit a protective immune response. The need for a vaccine against this pathogen is well recognized and a number of vaccine candidates have been tested with varying degrees of success; however, there is still a lack of a suitable vaccine. To gain a better understanding of the outer-membrane protein components of this organism, a 'gold standard' method to purify the outer membrane is needed. Therefore, we attempted to develop a robust and reliable method which resulted in a pure outer-membrane fraction. A total of nine methodologies were examined and analysed by SDS-PAGE and immunoblotting using subcellular markers for the cytoplasm, cytoplasmic membrane and outer membrane. We found that glycine extraction, differential detergent extraction using Triton X-100, serial extraction using 1 M Tris pH 7, spheroplasting by lysozyme and sonication, and carbonate extraction did not produce pure outer-membrane preparations. However, we identified three methods that provided outer-membrane fractions free from subcellular contamination. Isopycnic centrifugation using a 30-60 % sucrose gradient produced seven fractions free from cytoplasmic or cytoplasmic membrane contamination; however, these fractions did not correspond as well as expected with the typical outer-membrane-associated peak (e.g. Escherichia coli or Salmonella). The spheroplast method using lysozyme alone also resulted in pure outer-membrane fraction, as did carbonate washing of this sample. The extraction of outer membranes using N-lauroylsarcosine (Sarkosyl) produced the purest and most reproducible sample. These outer-membrane preparations will be useful for future studies aimed at identifying C. jejuni surface proteins as vaccine components.

Monoclonal antibody binding to the major outer membrane protein of Campylobacter coli

Campylobacter species are major enteric pathogens causing diarrhea illness in humans and animals. Immunological tests are needed for accurate and rapid identification of C. coli, in conjunction with the use of standard biochemical tests. We initiated the creation of monoclonal antibodies (MAbs) using whole C. coli cells as antigen. Four positive clones were identified, namely MAb2G6, MAb3B9, MAb4A10 and MAb5B9. Dot-blot assay and ELISA revealed that only MAb2G6 did not cross react with C. jejuni and other Campylobacter isolates. As demonstrated by dot-blot assay, MAb2G6 reacted with all 23 C. coli isolates tested but did not react with 29 isolates of C. jejuni, 3 other Campylobacter spp. isolates and 19 non-Campylobacter isolates, with the lowest detection limit was in the range of 10(3) to 10(4) bacteria. Western blots and dot blots showed that the antigen of MAb2G6 was a native protein, with immunoprecipitation assay showed that MAb2G6 bound to a protein band of approximately 43 kDa in size, corresponding to major outer membrane protein (MOMP) of C. coli revealed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). Immunofluorescence assay (IFA) showed that MOMP of C. coli was indeed the antigen of MAb2G6, with immunogold-electron microscopy demonstrated that MAb2G6 conjugated with immunogold particles bound to all over the surface of C. coli cells. MAb2G6 also showed potential usage in direct detection of C. coli in faecal samples.

Incidence and ecology of Campylobacter jejuni and coli in animals

Since its initial emergence in the 1970s, Campylobacter has become one of the most common causative agents of bacterial foodborne illness. Campylobacter species readily colonize the gastrointestinal tracts of domestic, feral and wild animals and while they rarely cause clinical disease in food animals, they can produce severe acute gastroenteritis in humans. Prevalence of Campylobacter in food animals can exceed 80% thus challenging processors to employ post-harvest pathogen reduction strategies. Reduction of pathogens before arrival to the abattoir is also of interest because the implementation of pre-harvest interventions may compliment existing post-harvest control techniques to further diminish possible retail sources of infection. Such multiple hurdle approaches that simultaneously utilize pre- and post-harvest control techniques are expected to be the most effective approach for decreasing human illness associated with foodborne pathogens.

Expression and porin activity of P28 and OMP-1F during intracellular Ehrlichia chaffeensis development

Ehrlichia chaffeensis, an obligatory intracellular gram-negative bacterium, must take up various nutrients and metabolic compounds because it lacks many genes involved in metabolism. Nutrient uptake by a gram-negative bacterium occurs primarily through pores or channels in the bacterial outer membrane. Here we demonstrate that isolated E. chaffeensis outer membranes have porin activities, as determined by a proteoliposome swelling assay. The activity was partially blocked by an antibody that recognizes the two most abundant outer membrane proteins, P28/OMP-19 and OMP-1F/OMP-18. Both proteins were predicted to have structural features characteristic of porins, including 12 transmembrane segments comprised of amphipathic and antiparallel beta-strands. The sodium dodecyl sulfate stability of the two proteins was consistent with a beta-barrel structure. Isolated native P28 and OMP-1F exhibited porin activities, with pore sizes similar to and larger than, respectively, that of OprF, which is the porin with the largest pore size known to date. E. chaffeensis experiences temperature changes during transmission by ticks. During the intracellular development of E. chaffeensis, both P28 and OMP-1F were expressed mostly in the mid-exponential growth phase at 37 degrees C and the late-exponential growth phase at 28 degrees C. The porin activity of proteoliposomes reconstituted with proteins from the outer membrane fractions derived from bacteria in the mid- and late-exponential growth phases at 28 degrees C and 37 degrees C correlated with the expression levels of P28 and OMP-1F. These results imply that P28 and OMP-1F function as porins with large pore sizes, suggesting that the differential expression of these two proteins might regulate nutrient uptake during intracellular E. chaffeensis development at both temperatures.

Emergence of a tetracycline-resistant Campylobacter jejuni clone associated with outbreaks of ovine abortion in the United States

Campylobacter infection is one of the major causes of ovine abortions worldwide. Historically, Campylobacter fetus subsp. fetus was the major cause of Campylobacter-associated abortion in sheep; however, Campylobacter jejuni is increasingly associated with sheep abortions. We examined the species distribution, genotypes, and antimicrobial susceptibilities of abortion-associated Campylobacter isolates obtained from multiple lambing seasons on different farms in Iowa, Idaho, South Dakota, and California. We found that C. jejuni has replaced C. fetus as the predominant Campylobacter species causing sheep abortion in the United States. Most strikingly, the vast majority (66 of 71) of the C. jejuni isolates associated with sheep abortion belong to a single genetic clone, as determined by pulsed-field gel electrophoresis, multilocus sequence typing, and cmp gene (encoding the major outer membrane protein) sequence typing. The in vitro antimicrobial susceptibilities of these isolates to the antibiotics that are routinely used in food animal production were determined using the agar dilution test. All of the 74 isolates were susceptible to tilmicosin, florfenicol, tulathromycin, and enrofloxacin, and 97% were sensitive to tylosin. However, all were resistant to tetracyclines, the only antibiotics currently approved in the United States for the treatment of Campylobacter abortion in sheep. This finding suggests that feeding tetracycline for the prevention of Campylobacter abortions is ineffective and that other antibiotics should be used for the treatment of sheep abortions in the United States. Together, these results indicate that a single tetracycline-resistant C. jejuni clone has emerged as the major cause of Campylobacter-associated sheep abortion in the United States.

Production of a monoclonal antibody specific for the major outer membrane protein of Campylobacter jejuni and characterization of the epitope

Campylobacter species are important enteric pathogens causing disease in humans and animals. There is a lack of a good immunological test that can be used routinely to separate Campylobacter jejuni from other Campylobacter species. We produced monoclonal antibodies (MAbs) directed against the major outer membrane protein (MOMP) of C. jejuni using recombinant MOMP as the antigen. One MAb, designated MAb5C4 and of the immunoglobulin G1 isotype, was found to be potentially specific for C. jejuni. Dot blots demonstrated that MAb5C4 reacted with all 29 isolates of C. jejuni tested but did not react with 2 C. jejuni isolates, 26 other Campylobacter spp. isolates, and 19 non-Campylobacter isolates. Western blotting showed that MAb5C4 bound to a single protein band approximately 43 kDa in size, corresponding to the expected size of C. jejuni MOMP. The detection limit of MAb5C4 in a dot blot assay was determined to be about 5 x 10(3) bacteria. The epitope on the MOMP was mapped to a region six amino acids in length with the sequence 216GGQFNP221, which is 97% conserved among C. jejuni strains but divergent in other Campylobacter spp.; a GenBank search indicated that 95% of C. jejuni isolates will be able to be detected from non-Campylobacter spp. based on the highly specific and conserved region of the GGQFNP polypeptide. The epitope is predicted to be located in a region that is exposed to the periplasm. MAb5C4 is a potentially specific and sensitive MAb that can be used for the specific detection and identification of C. jejuni.