Identification of surface-exposed outer membrane antigens of Helicobacter pylori

A Tripartite Efflux System Affects Flagellum Stability in Helicobacter pylori

Helicobacter pylori uses a cluster of polar, sheathed flagella for swimming motility. A search for homologs of H. pylori proteins that were conserved in Helicobacter species that possess flagellar sheaths but were underrepresented in Helicobacter species with unsheathed flagella identified several candidate proteins. Four of the identified proteins are predicted to form part of a tripartite efflux system that includes two transmembrane domains of an ABC transporter (HP1487 and HP1486), a periplasmic membrane fusion protein (HP1488), and a TolC-like outer membrane efflux protein (HP1489). Deleting hp1486/hp1487 and hp1489 homologs in H. pylori B128 resulted in reductions in motility and the number of flagella per cell. Cryo-electron tomography studies of intact motors of the Δhp1489 and Δhp1486/hp1487 mutants revealed many of the cells contained a potential flagellum disassembly product consisting of decorated L and P rings, which has been reported in other bacteria. Aberrant motors lacking specific components, including a cage-like structure that surrounds the motor, were also observed in the Δhp1489 mutant. These findings suggest a role for the H. pylori HP1486-HP1489 tripartite efflux system in flagellum stability. Three independent variants of the Δhp1486/hp1487 mutant with enhanced motility were isolated. All three motile variants had the same frameshift mutation in fliL, suggesting a role for FliL in flagellum disassembly.

Phylogenetic Distribution, Ultrastructure, and Function of Bacterial Flagellar Sheaths

A number of Gram-negative bacteria have a membrane surrounding their flagella, referred to as the flagellar sheath, which is continuous with the outer membrane. The flagellar sheath was initially described in Vibrio metschnikovii in the early 1950s as an extension of the outer cell wall layer that completely surrounded the flagellar filament. Subsequent studies identified other bacteria that possess flagellar sheaths, most of which are restricted to a few genera of the phylum Proteobacteria. Biochemical analysis of the flagellar sheaths from a few bacterial species revealed the presence of lipopolysaccharide, phospholipids, and outer membrane proteins in the sheath. Some proteins localize preferentially to the flagellar sheath, indicating mechanisms exist for protein partitioning to the sheath. Recent cryo-electron tomography studies have yielded high resolution images of the flagellar sheath and other structures closely associated with the sheath, which has generated insights and new hypotheses for how the flagellar sheath is synthesized. Various functions have been proposed for the flagellar sheath, including preventing disassociation of the flagellin subunits in the presence of gastric acid, avoiding activation of the host innate immune response by flagellin, activating the host immune response, adherence to host cells, and protecting the bacterium from bacteriophages.

The unique trimeric assembly of the virulence factor HtrA from Helicobacter pylori occurs via N-terminal domain swapping

Knowledge of the molecular mechanisms of specific bacterial virulence factors can significantly contribute to antibacterial drug discovery. Helicobacter pylori is a Gram-negative microaerophilic bacterium that infects almost half of the world's population, leading to gastric disorders and even gastric cancer. H. pylori expresses a series of virulence factors in the host, among which high-temperature requirement A (HpHtrA) is a newly identified serine protease secreted by H. pylori. HpHtrA cleaves the extracellular domain of the epithelial cell surface adhesion protein E-cadherin and disrupts gastric epithelial cell junctions, allowing H. pylori to access the intercellular space. Here we report the first crystal structure of HpHtrA at 3.0 Å resolution. The structure revealed a new type of HtrA protease trimer stabilized by unique N-terminal domain swapping distinct from other known HtrA homologs. We further observed that truncation of the N terminus completely abrogates HpHtrA trimer formation as well as protease activity. In the presence of unfolded substrate, HpHtrA assembled into cage-like 12-mers or 24-mers. Combining crystallographic, biochemical, and mutagenic data, we propose a mechanistic model of how HpHtrA recognizes and cleaves the well-folded E-cadherin substrate. Our study provides a fundamental basis for the development of anti-H. pylori agents by using a previously uncharacterized HtrA protease as a target.

Reductive evolution in outer membrane protein biogenesis has not compromised cell surface complexity in Helicobacter pylori

Helicobacter pylori is a gram‐negative bacterial pathogen that chronically inhabits the human stomach. To survive and maintain advantage, it has evolved unique host–pathogen interactions mediated by Helicobacter‐specific proteins in the bacterial outer membrane. These outer membrane proteins (OMPs) are anchored to the cell surface via a C‐terminal β‐barrel domain, which requires their assembly by the β‐barrel assembly machinery (BAM). Here we have assessed the complexity of the OMP C‐terminal β‐barrel domains employed by H. pylori, and characterized the H. pyloriBAM complex. Around 50 Helicobacter‐specific OMPs were assessed with predictive structural algorithms. The data suggest that H. pylori utilizes a unique β‐barrel architecture that might constitute H. pylori‐specific Type V secretions system. The structural and functional diversity in these proteins is encompassed by their extramembrane domains. Bioinformatic and biochemical characterization suggests that the low β‐barrel‐complexity requires only minimalist assembly machinery. The H. pylori proteins BamA and BamD associate to form a BAM complex, with features of BamA enabling an oligomerization that might represent a mechanism by which a minimalist BAM complex forms a larger, sophisticated machinery capable of servicing the outer membrane proteome of H. pylori.

Characterization of Key Helicobacter pylori Regulators Identifies a Role for ArsRS in Biofilm Formation

Helicobacter pylori must be able to rapidly respond to fluctuating conditions within the stomach. Despite this need for constant adaptation, H. pylori encodes few regulatory proteins. Of the identified regulators, the ferric uptake regulator (Fur), the nickel response regulator (NikR), and the two-component acid response system (ArsRS) are each paramount to the success of this pathogen. While numerous studies have individually examined these regulatory proteins, little is known about their combined effect. Therefore, we constructed a series of isogenic mutant strains that contained all possible single, double, and triple regulatory mutations in Fur, NikR, and ArsS. A growth curve analysis revealed minor variation in growth kinetics across the strains; these were most pronounced in the triple mutant and in strains lacking ArsS. Visual analysis showed that strains lacking ArsS formed large aggregates and a biofilm-like matrix at the air-liquid interface. Biofilm quantification using crystal violet assays and visualization via scanning electron microscopy (SEM) showed that all strains lacking ArsS or containing a nonphosphorylatable form of ArsR (ArsR-D52N mutant) formed significantly more biofilm than the wild-type strain. Molecular characterization of biofilm formation showed that strains containing mutations in the ArsRS pathway displayed increased levels of cell aggregation and adherence, both of which are key to biofilm development. Furthermore, SEM analysis revealed prevalent coccoid cells and extracellular matrix formation in the ArsR-D52N, ΔnikR ΔarsS, and Δfur ΔnikR ΔarsS mutant strains, suggesting that these strains may have an exacerbated stress response that further contributes to biofilm formation. Thus, H. pylori ArsRS has a previously unrecognized role in biofilm formation.

IMPORTANCE

Despite a paucity of regulatory proteins, adaptation is key to the survival of H. pylori within the stomach. While prior studies have focused on individual regulatory proteins, such as Fur, NikR, and ArsRS, few studies have examined the combined effect of these factors. Analysis of isogenic mutant strains that contained all possible single, double, and triple regulatory mutations in Fur, NikR, and ArsS revealed a previously unrecognized role for the acid-responsive two-component system ArsRS in biofilm formation.

Immunoproteomic Approach for Screening Vaccine Candidates from Bacterial Outer Membrane Proteins

Outer membrane proteins (OMPs) are unique to Gram-negative bacteria and have been revealed as potential vaccine candidates for conferring protection against infections in recent years. Immunoproteomics is a powerful technique that is ideally suited to screen and identify potential vaccine candidates. This chapter presents a brief outline of the screening of immunogenic OMPs from Vibrio parahaemolyticus by an immunoproteomic strategy that was based on two-dimensional electrophoresis (2-DE) and immunoblotting. The protective efficacy provided by the immunogenic OMP Vp0802 determined by active protection experiment assays is also presented in brief.

Analysis of surface-exposed outer membrane proteins in Helicobacter pylori

More than 50 Helicobacter pylori genes are predicted to encode outer membrane proteins (OMPs), but there has been relatively little experimental investigation of the H. pylori cell surface proteome. In this study, we used selective biotinylation to label proteins localized to the surface of H. pylori, along with differential detergent extraction procedures to isolate proteins localized to the outer membrane. Proteins that met multiple criteria for surface-exposed outer membrane localization included known adhesins, as well as Cag proteins required for activity of the cag type IV secretion system, putative lipoproteins, and other proteins not previously recognized as cell surface components. We identified sites of nontryptic cleavage consistent with signal sequence cleavage, as well as C-terminal motifs that may be important for protein localization. A subset of surface-exposed proteins were highly susceptible to proteolysis when intact bacteria were treated with proteinase K. Most Hop and Hom OMPs were susceptible to proteolysis, whereas Hor and Hof proteins were relatively resistant. Most of the protease-susceptible OMPs contain a large protease-susceptible extracellular domain exported beyond the outer membrane and a protease-resistant domain at the C terminus with a predicted β-barrel structure. These features suggest that, similar to the secretion of the VacA passenger domain, the N-terminal domains of protease-susceptible OMPs are exported through an autotransporter pathway. Collectively, these results provide new insights into the repertoire of surface-exposed H. pylori proteins that may mediate bacterium-host interactions, as well as the cell surface topology of these proteins.

Comparative proteomics analysis of sarcosine insoluble outer membrane proteins from clarithromycin resistant and sensitive strains of Helicobacter pylori

Helicobacter pylori causes disease manifestations in humans including chronic gastric and peptic ulcers, gastric cancer, and lymphoid tissue lymphoma. Increasing rates of H. pylori clarithromycin resistance has led to higher rates of disease development. Because antibiotic resistance involves modifications of outer membrane proteins (OMP) in other Gram-negative bacteria, this study focuses on identification of H. pylori OMP's using comparative proteomic analyses of clarithromycin-susceptible and -resistant H. pylori strains. Comparative proteomics analyses of isolated sarcosine-insoluble OMP fractions from clarithromycin-susceptible and -resistant H. pylori strains were performed by 1) one dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis protein separation and 2) in-gel digestion of the isolated proteins and mass spectrometry analysis by Matrix Assisted Laser Desorption Ionization-tandem mass spectrometry. Iron-regulated membrane protein, UreaseB, EF-Tu, and putative OMP were down-regulated; HopT (BabB) transmembrane protein, HofC, and OMP31 were up-regulated in clarithromycin-resistant H. pylori. Western blotting and real time PCR, respectively, validated UreaseB subunit and EF-Tu changes at the protein level, and mRNA expression of HofC and HopT. This limited proteomic study provides evidence that alteration of the outer membrane proteins' profile may be a novel mechanism involved in clarithromycin resistance in H. pylori.

Cag type IV secretion system: CagI independent bacterial surface localization of CagA

Helicobacter pylori Cag type IV secretion system (Cag-T4SS) is a multi-component transporter of oncoprotein CagA across the bacterial membranes into the host epithelial cells. To understand the role of unique Cag-T4SS component CagI in CagA translocation, we have characterized it by biochemical and microscopic approaches. We observed that CagI is a predominantly membrane attached periplasmic protein partially exposed to the bacterial surface especially on the pili. The association of the protein with membrane appeared to be loose as it could be easily recovered in soluble fraction. We documented that the stability of the protein is dependent on several key components of the secretion system and it has multiple interacting partners including a non-cag-PAI protein HP1489. Translocation of CagA across the bacterial membranes to cell surface is CagI-independent process. The observations made herein are expected to assist in providing an insight into the substrate translocation by the Cag-T4SS system and Helicobacter pylori pathogenesis.

Protein glycosylation in Helicobacter pylori: beyond the flagellins?

Glycosylation of flagellins by pseudaminic acid is required for virulence in Helicobacter pylori. We demonstrate that, in H. pylori, glycosylation extends to proteins other than flagellins and to sugars other than pseudaminic acid. Several candidate glycoproteins distinct from the flagellins were detected via ProQ-emerald staining and DIG- or biotin- hydrazide labeling of the soluble and outer membrane fractions of wild-type H. pylori, suggesting that protein glycosylation is not limited to the flagellins. DIG-hydrazide labeling of proteins from pseudaminic acid biosynthesis pathway mutants showed that the glycosylation of some glycoproteins is not dependent on the pseudaminic acid glycosylation pathway, indicating the existence of a novel glycosylation pathway. Fractions enriched in glycoprotein candidates by ion exchange chromatography were used to extract the sugars by acid hydrolysis. High performance anion exchange chromatography with pulsed amperometric detection revealed characteristic monosaccharide peaks in these extracts. The monosaccharides were then identified by LC-ESI-MS/MS. The spectra are consistent with sugars such as 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-nonulosonic acid (Pse5Ac7Ac) previously described on flagellins, 5-acetamidino-7-acetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-nonulosonic acid (Pse5Am7Ac), bacillosamine derivatives and a potential legionaminic acid derivative (Leg5AmNMe7Ac) which were not previously identified in H. pylori. These data open the way to the study of the mechanism and role of protein glycosylation on protein function and virulence in H. pylori.

Identification of Helicobacter pylori strain cagPAI+ and cagPAI- Antigens by IgG antibodies from sera of experimentally colonized meriones unguiculatus (Mongolian gerbils)

BACKGROUND

 Mongolian gerbils that are experimentally infected with Helicobacter pylori develop a chronic inflammation that is similar to natural infections in humans. The aim of this study was to compare the antigens of H. pylori cagPAI+ and cagPAI- strains that are expressed during Meriones unguiculatus colonization.

MATERIALS AND METHODS

 We identified H. pylori cagPAI+ and cagPAI- strain antigens via Western blotting of samples from Mongolian gerbils that were subjected to unique, mixed, and sequential bacterial infections.

RESULTS

 The antigens from the J99/CG3 (cagPAI+) strain had a lower molecular weight than the antigens from the 251F/CG3 (cagPAI-) strain. There were fewer identified antigens in the single unique infections compared with the mixed and sequential infections. The number of recognized antigens that had a frequency of recognition >60% was higher for the simultaneous and sequential infection groups compared with the single infection group. A 57-kDa antigen was present in >60% of the samples and four of the five experimental groups. Antigens specific to each bacterial strain were identified; the 190- and 158-kDa antigens appear to be specific for cagPAI-, and the 70-kDa antigen appears to be specific for cagPAI+.

CONCLUSIONS

 In this study, we identified antigens that are common and specific to the H. pylori cagPAI+ and cagPAI- strains.

Morphological analysis of the sheathed flagellum of Brucella melitensis

Background

It was recently shown that B. melitensis is flagellated. However, the flagellar structure remains poorly described.

Findings

We analyzed the structure of the polar sheathed flagellum of B. melitensis by TEM analysis and demonstrated that the Ryu staining is a good method to quickly visualize the flagellum by optical microscopy. The TEM analysis demonstrated that an extension of the outer membrane surrounds a filament ending by a club-like structure. The ΔftcR, ΔfliF, ΔflgE and ΔfliC flagellar mutants still produce an empty sheath.

Conclusions

Our results demonstrate that the flagellum of B. melitensis has the characteristics of the sheathed flagella. Our results also suggest that the flagellar sheath production is not directly linked to the flagellar structure assembly and is not regulated by the FtcR master regulator.

Ferrous iron-binding protein Omb of Salmonella enterica serovar Choleraesuis promotes resistance to hydrophobic antibiotics and contributes to its virulence

Salmonella enterica serovar Choleraesuis (SC) is an important enteric pathogen that causes serious systemic infections in swine and humans. To identify the genes required for resistance to antimicrobial peptides, we constructed a bank of SC transposon mutants and screened them for hypersensitivity to the cationic peptide polymyxin B. Here we report one isolated polymyxin B-susceptible mutant that also exhibited increased sensitivity toward human neutrophil peptide alpha-defensin 1 (HNP-1) and hydrophobic antibiotics including erythromycin and novobiocin. The mutant had a mutation in an ORF identified as outer membrane beta-barrel protein gene omb. The purified recombinant Omb protein was characterized as a ferrous iron-binding protein. The constructed omb isogenic mutant grew more slowly in iron-limiting conditions than the wild-type (WT) parent strain. In addition, compared with the WT strain, the omb mutant exhibited an increase in net negative charge upon the cell surface and was more easily killed by polymyxin B, HNP-1 and hydrophobic antibiotics. The omb gene was transcribed, regardless of the iron content within the growth medium, and the Omb protein appeared exclusively in the outer membrane fraction. Infection experiments demonstrated virulence attenuation when the mutant was administered orally or intraperitoneally to mice. This study indicates that Omb is a previously unrecognized ferrous iron-binding protein. In vivo, Omb may be involved in the acquisition of ferrous iron during the initial stages of SC infection and appears to be an important virulence factor for SC in mice.

The role of heparan sulfate on adhesion of 47 and 51 kDa outer membrane proteins ofHelicobacter pylorito gastric cancer cellsThis study was done in memory of the late Dr. Roberto Carlos Vazquez-Juarez

Helicobacter pylori is a common gastrointestinal pathogenic bacterium in humans and the usual preference for the stomach’s outer membrane proteins (OMPs) are antigens involved in the adhesion process. Through SDS–PAGE and blotting analyses, using horseradish peroxidase-labeled heparan sulfate (HRP-HS) as a probe, we identified H. pylori OMPs with affinity for heparan sulfate (OMP-HS). Biotin–streptavidin bacterial-adhesion assay was used to evaluate participation of OMP-HS in the adhesion of H. pylori to semi-confluent HeLa S3 and Kato III cell monolayers. The results provide evidence that induction of antibodies against 2 OMP-HSs (HSBP-47 and HSBP-51) could reduce binding of H. pylori to both cell lines and induce detachment of cell-bound bacteria from infected cultured cells.

Helicobacter pylori lipopolysaccharide interacts with TFF1 in a pH-dependent manner

BACKGROUND & AIMS

Little is known about how bacteria establish chronic infections of mucosal surfaces. Helicobacter pylori (H. pylori), a chronic pathogen that lives in the gastric mucosa of humans, interacts with the trefoil factor family (TFF) protein TFF1, which is found in gastric mucus. We aimed to characterize the interaction of H. pylori with TFF1 and to assess the role of this interaction in mediating colonization.

METHODS

Subcellular fractions of H. pylori were immobilized and then probed with TFF1, TFF2, or TFF3. The effect of glycosidases and preincubation with monosaccharides on the interaction and binding of TFF1 to a H. pylori adhesin was assessed. The interaction between H. pylori adhesin and TFF1 was characterized using surface plasmon resonance, flow cytometry, nondenaturing polyacrylamide gel electrophoresis, coimmunofluoresence, and incubation with tissue sections.

RESULTS

The H. pylori core oligosaccharide portion (rough form) of lipopolysaccharide (RF-LPS) bound to TFF1 and to a lesser extent TFF3; this interaction was inhibited by incubation of RF-LPS with mannosidase, glucosidase, or mixed monosaccharides. TFF1 also bound to human serum albumin-conjugated mannose and glucose. The optimum pH for binding was 5.0-6.0 for TFF1 and 7.0 for TFF3. H. pylori bound TFF1 in gastric mucus ex vivo; binding of LPS-coated latex beads to human antral gastric tissue was inhibited by TFF1.

CONCLUSIONS

TFF1 interacts specifically with H. pylori RF-LPS. The pH dependence of this interaction indicates that binding of H. pylori to TFF1 in the stomach could promote colonization of the mucus layer adjacent to the gastric epithelial surface.

Protein subassemblies of the Helicobacter pylori Cag type IV secretion system revealed by localization and interaction studies

Type IV secretion systems are possibly the most versatile protein transport systems in gram-negative bacteria, with substrates ranging from small proteins to large nucleoprotein complexes. In many cases, such as the cag pathogenicity island of Helicobacter pylori, genes encoding components of a type IV secretion system have been identified due to their sequence similarities to prototypical systems such as the VirB system of Agrobacterium tumefaciens. The Cag type IV secretion system contains at least 14 essential apparatus components and several substrate translocation and auxiliary factors, but the functions of most components cannot be inferred from their sequences due to the lack of similarities. In this study, we have performed a comprehensive sequence analysis of all essential or auxiliary Cag components, and we have used antisera raised against a subset of components to determine their subcellular localization. The results suggest that the Cag system contains functional analogues to all VirB components except VirB5. Moreover, we have characterized mutual stabilization effects and performed a comprehensive yeast two-hybrid screening for potential protein-protein interactions. Immunoprecipitation studies resulted in identification of a secretion apparatus subassembly at the outer membrane. Combining these data, we provide a first low-resolution model of the Cag type IV secretion apparatus.

A surface-focused biotinylation procedure identifies the Yersinia pestis catalase KatY as a membrane-associated but non-surface-located protein

This study identified major surface proteins of the plague bacterium Yersinia pestis. We applied a novel surface biotinylation method, followed by NeutrAvidin (NA) bead capture, on-bead digestion, and identification by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The use of stachyose during biotinylation focused the reaction to the surface. Coupled with NA pulldown and immunoblot analysis, this method determined whether a protein was accessible to the surface. We applied the method to test the hypothesis that the catalase KatY is a surface protein of the plague bacterium Y. pestis. A rabbit serum recognized the catalase KatY as a major putative outer membrane-associated antigen expressed by Y. pestis cells grown at 37 degrees C. Similar findings by other groups had led to speculations that this protein might be exposed to the surface and might be a candidate for evaluation as a protective antigen for an improved plague vaccine. KatY was obtained only in the total membrane fraction, and stachyose greatly reduced its biotinylation as well as that of the periplasmic maltose binding protein, indicating that KatY is not on the bacterial surface. LC-MS-MS analysis of on-bead digests representing ca. 10(9) cells identified highly abundant species, including KatY, Pal, and OmpA, as well as the lipoprotein Pcp, all of which bound in a biotin-specific manner. Pla, Lpp, and OmpX (Ail) bound to the NA beads in a non-biotin-specific manner. There was no contamination from abundant cytoplasmic proteins. We hypothesize that OmpX and Pcp are highly abundant and likely to be important for the Y. pestis pathogenic process. We speculate that a portion of KatY associates with the outer membrane in intact cells but that it is located on the periplasmic side. Consistent with this idea, it did not protect C57BL/6 mice against bubonic plague.

HorB (HP0127) is a gastric epithelial cell adhesin

BACKGROUND

The Helicobacter pylori protein HorB (encoded by HP0127) is a member of a paralogous family that includes the adhesins BabA, AlpA, AlpB, and HopZ, which contribute to adhesion to gastric epithelial cells. Of the verified H. pylori porins, the HorB sequence is most similar to that of HopE, but the function of HorB is unknown. The aim of our study was to investigate the role of HorB in H. pylori gastric epithelial cell adhesion.

MATERIALS AND METHODS

We disrupted the horB gene in H. pylori and measured the adhesion to gastric epithelial cells (AGS cells). We then assessed the effect that HorB disruption had on lipopolysaccharide (LPS) O-chain production and Lewis x and Lewis y antigen expression. A HorB mutant in the mouse-adapted strain H. pylori SS1 was created by marker exchange and mouse stomach colonization was quantified. Using reverse transcription polymerase chain reaction, human gastric biopsy material from H. pylori-infected patients was then examined for expression of the horB gene.

RESULTS

Disruption of the horB gene reduced H. pylori adhesion by more than twofold. Adhesion in the horB knockout strain was restored to wild-type levels by re-introduction of HorB into the chromosome. Disruption of HorB reduced production of LPS O-chains and lowered the level of expression of Lewis x and Lewis y antigens. Insertional mutagenesis of the horB gene in H. pylori SS1 reduced mouse stomach colonization threefold. Finally, expression of the horB gene was detected in human gastric biopsy material from H. pylori-infected patients.

CONCLUSIONS

From these data we conclude that HorB has a role in H. pylori adhesion during infection.

Characterization of the outer membrane protein profile from disease-related Helicobacter pylori isolates by subcellular fractionation and nano-LC FT-ICR MS analysis

Because of the important role of membrane proteins in adhesion, invasion, and intracellular survival of pathogens in the host, membrane proteins are of potential interest in the search for drug targets or biomarkers. We have established a mass spectrometry-based method that allows characterization of the outer membrane protein (OMP) profile of clinical isolates from of the human gastric pathogen Helicobacter pylori. Subcellular fractionation and one-dimensional gel electrophoresis (1D-GE) analysis was combined with nano-liquid chromatography Fourier transform-ion cyclotron resonance mass spectrometry (nano-LC FT-ICR MS) and tandem mass spectrometry (MS/MS) analysis of fifteen H. pylori strains associated either with duodenal ulcers, gastric cancer, or isolated from asymptomatic H. pylori infected carriers. Over 60 unique membrane or membrane-associated proteins, including 30 of the 33 theoretically predicted OMPs, were identified from the strains. Several membrane proteins, including Omp11 and BabA, were found to be expressed by all strains. In the search for clinical markers we found that Omp26 was expressed by all disease-related strains but was only present in one out of five strains from asymptomatic carriers, which makes Omp26 a potential target for further investigation in the search for proteins unique to disease-related H. pylori strains. In addition, presence of Omp30 and absence of Omp6 seemed to be associated with H. pylori strains causing duodenal ulcer.

Flagellar glycosylation - a new component of the motility repertoire?

The biosynthesis, assembly and regulation of the flagellar apparatus has been the subject of extensive studies over many decades, with considerable attention devoted to the peritrichous flagella of Escherichia coli and Salmonella enterica. The characterization of flagellar systems from many other bacterial species has revealed subtle yet distinct differences in composition, regulation and mode of assembly of this important subcellular structure. Glycosylation of the major structural protein, the flagellin, has been shown most recently to be an important component of numerous flagellar systems in both Archaea and Bacteria, playing either an integral role in assembly or for a number of bacterial pathogens a role in virulence. This review focuses on the structural diversity in flagellar glycosylation systems and demonstrates that as a consequence of the unique assembly processes, the type of glycosidic linkage found on archaeal and bacterial flagellins is distinctive.

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori.

HpaA is essential for Helicobacter pylori colonization in mice

Infection with the human gastric pathogen Helicobacter pylori can give rise to chronic gastritis, peptic ulcer, and gastric cancer. All H. pylori strains express the surface-localized protein HpaA, a promising candidate for a vaccine against H. pylori infection. To study the physiological importance of HpaA, a mutation of the hpaA gene was introduced into a mouse-adapted H. pylori strain. To justify that the interruption of the hpaA gene did not cause any polar effects of downstream genes or was associated with a second site mutation, the protein expression patterns of the mutant and wild-type strains were characterized by two different proteomic approaches. Two-dimensional differential in-gel electrophoresis analysis of whole-cell extracts and subcellular fractionation combined with nano-liquid chromatography-Fourier transform ion cyclotron resonance mass spectrometry for outer membrane protein profiling revealed only minor differences in the protein profile between the mutant and the wild-type strains. Therefore, the mutant strain was tested for its colonizing ability in a well-established mouse model. While inoculation with the wild-type strain resulted in heavily H. pylori-infected mice, the HpaA mutant strain was not able to establish colonization. Thus, by combining proteomic analysis and in vivo studies, we conclude that HpaA is essential for the colonization of H. pylori in mice.

Variations in Helicobacter pylori lipopolysaccharide to evade the innate immune component surfactant protein D

Helicobacter pylori is a common and persistent human pathogen of the gastric mucosa. Surfactant protein D (SP-D), a component of innate immunity, is expressed in the human gastric mucosa and is capable of aggregating H. pylori. Wide variation in the SP-D binding affinity to H. pylori has been observed in clinical isolates and laboratory-adapted strains. The aim of this study was to reveal potential mechanisms responsible for evading SP-D binding and establishing persistent infection. An escape variant, J178V, was generated in vitro, and the lipopolysaccharide (LPS) structure of the variant was compared to that of the parental strain, J178. The genetic basis for structural variation was explored by sequencing LPS biosynthesis genes. SP-D binding to clinical isolates was demonstrated by fluorescence-activated cell sorter analyses. Here, we show that H. pylori evades SP-D binding through phase variation in lipopolysaccharide. This phenomenon is linked to changes in the fucosylation of the O chain, which was concomitant with slipped-strand mispairing in a poly(C) tract of the fucosyltransferase A (fucT1) gene. SP-D binding organisms are predominant in mucus in vivo (P = 0.02), suggesting that SP-D facilitates physical elimination. Phase variation to evade SP-D contributes to the persistence of this common gastric pathogen.

Identification of Helicobacter pylori surface proteins by selective proteinase K digestion and antibody phage display

Five surface proteins of Helicobacter pylori were identified by proteinase K treatment of live H. pylori followed by proteome analysis. One of the identified proteins, HopQ, is also recognized by an antibody selected by phage display screening of intact H. pylori.

Expression of Helicobacter pylori AlpA protein and its immunogenicity

AIM: To construct a recombinant strain which expresses adhesin AlpA of Helicobacter pylori (H pylori ) and to study the immunogenicity of adhesin AlpA.

METHODS: Gene Ab, which was amplified from H pylori chromosomal DNA by PCR technique, was sequenced and the biological information was analyzed, and inserted into the Nco I and Not I restriction fragments of the expression vector pET-22b(+) using T4 DNA ligase. The resulting plasmid pET-AlpA was transformed into competent E.coli BL21(DE3) cells using ampicillin resistance for selection. Recombinant strains were incubated in 5 mL LB with 100 μg/mL ampicillin overnight at 37 °C. Sonication of BL21(DE3)pET-22b(+)/AlpA was analyzed by Western blot to detect AlpA immunogenicity.

RESULTS: The gene encoding AlpA protein was amplified by PCR with chromosomal DNA of H pylori Sydney strain (SS1) as templates. It revealed that AlpA DNA fragment amplified by PCR had approximately 1 500 nucleotides, compatible with the previous reports. The recombinant plasmid pET-22b(+)/AB was successfully constructed. DNA sequencing showed one open reading frame with the length of 588 bp. It encoded seven conservative regions that showed good antigenicity and hydrophobicity by Parker and Welling method. Furthermore, INTERNET EXPASY, NNPREDICT and ISREC predicted that it was a porin-like structure consisting of β-pleated sheets that were embedded in the outer membrane. BLAST analyzed 836 767 protein sequences and found that the similar sequences were all belonging to H pylori OMP sequences. SDS-PAGE and scan analysis showed that the molecular weight of AB was 22.5 ku and recombinant protein amounted to 29% of the total bacterial protein, among which dissolved expression amounted to 21.9% of sonicated supernatant. The rAB purity amounted to 96% through affinity chromatography. Western blot analysis of rAB confirmed that it could be specially recognized by serum form rabbit immunized with AlpA and H pylori infected.

CONCLUSION: Adhesin AlpA recombinant protein may be a potential vaccine for control and treatment of H pylori infection.

Characterization of cinnamyl alcohol dehydrogenase of Helicobacter pylori. An aldehyde dismutating enzyme

Cinnamyl alcohol dehydrogenases (CAD; 1.1.1.195) catalyse the reversible conversion of p-hydroxycinnamaldehydes to their corresponding alcohols, leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helicobacter pylori (HpCAD) was cloned in Escherichia coli and the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium. It is specific for NADP(H) as cofactor and has a broad substrate specificity for alcohol and aldehyde substrates. Its substrate specificity is similar to the well-characterized plant enzymes. High substrate inhibition was observed and a mechanism of competitive inhibition proposed. The enzyme was found to be capable of catalysing the dismutation of benzaldehyde to benzyl alcohol and benzoic acid. This dismutation reaction has not been shown previously for this class of alcohol dehydrogenase and provides the bacterium with a means of reducing aldehyde concentration within the cell.

Proteomic analysis of the sarcosine-insoluble outer membrane fraction of Helicobacter pylori strain 26695

Helicobacter pylori causes gastroduodenal disease, which is mediated in part by its outer membrane proteins (OMPs). To identify OMPs of H. pylori strain 26695, we performed a proteomic analysis. A sarcosine-insoluble outer membrane fraction was resolved by two-dimensional electrophoresis with immobilized pH gradient strips. Most of the protein spots, with molecular masses of 10 to 100 kDa, were visible on the gel in the alkaline pI regions (6.0 to 10.0). The proteome of the OMPs was analyzed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Of the 80 protein spots processed, 62 spots were identified; they represented 35 genes, including 16 kinds of OMP. Moreover, we identified 9 immunoreactive proteins by immunoblot analysis. This study contributes to the characterization of the H. pylori strain 26695 proteome and may help to further elucidate the biological function of H. pylori OMPs and the pathogenesis of H. pylori infection.

Induction of colitis by a CD4+ T cell clone specific for a bacterial epitope

It is now well established that the intestinal flora plays an important role in the pathogenesis of inflammatory bowel disease (IBD). However, whether bacteria serve as the sole target of the immune response in this process or whether they act indirectly by triggering an anti-self response is still unclear. We have previously shown that specific pathogen-free IL-10-deficient (IL-10 KO) mice develop a T helper (Th1)-cytokine associated colitis after experimental infection with Helicobacter hepaticus. We here show that H. hepaticus Ag (SHelAg)-specific CD4+ Th1 clones transfer disease to H. hepaticus-infected T cell-deficient RAG KO hosts. Importantly, uninfected recipients of the SHelAg-specific clones did not develop intestinal inflammation, and a control Schistosoma mansoni-specific Th1 clone did not induce colitis upon transfer to infected RAG KO mice. The disease-inducing T cell clones recognized antigen(s) (Ag) specifically expressed by certain Helicobacter species as they responded when stimulated in vitro with H. hepaticus and Helicobacter typhlonius Ag, but not when cultured with Ag preparations from Helicobacter pylori, various non-helicobacter bacteria, or with cecal bacterial lysate from uninfected mice. Characterization of the Ag specificity of one of the clones showed that it reacts uniquely with a 15-mer peptide epitope on the flagellar hook protein (FlgE) of H. hepaticus presented by I-Ab. Together, our results demonstrate that colitis can be induced by clonal T cell populations that are highly specific for target Ag on intestinal bacteria, suggesting that an aberrant T cell response directed against gut flora is sufficient to trigger IBD.

Recombinant HpaA purified from Escherichia coli has biological properties similar to those of native Helicobacter pylori HpaA

The aim of this study was to recombinantly produce and purify Helicobacter pylori adhesin A (HpaA) from Escherichia coli and compare it to purified native H. pylori HpaA, for potential use as a vaccine antigen. The hpaA gene was cloned from H. pylori, transferred to two different expression vectors, and transformed into E. coli. Expression of rHpaA was analysed by immunoblot, inhibition ELISA, and semi-quantitative dot-blot. Using affinity chromatography, rHpaA was purified from E. coli and native HpaA from H. pylori. The binding of both purified proteins to sialic acid was analysed and antibody titres to native and rHpaA were compared after intraperitoneal immunisation of C57/Bl mice. The rHpaA protein was highly expressed in E. coli from both vectors. Purified recombinant and native HpaA bound similarly to fetuin but also to the non-sialylated asialofetuin. Both native HpaA and rHpaA induced comparable amounts of specific antibodies in serum after immunisation and they were identical in double immunodiffusion. In conclusion, rHpaA was successfully produced in E. coli. Purified rHpaA showed biological properties similar to those of native HpaA isolated from H. pylori and may therefore be further used as an antigen in the development of a vaccine against H. pylori infection.

Characterization and immunogenicity of the CagF protein of the cag pathogenicity island of Helicobacter pylori

Helicobacter pylori infection causes severe gastroduodenal diseases in humans. Its virulence is strongly increased by the presence of the cag pathogenicity island (cag PAI). It has been shown that CagA, a major antigen in humans, is translocated to the host cell via a secretion system encoded by the cag PAI. The roles of many of the proteins encoded within the cag PAI are not known. Here we report on the cloning and expression of CagF, one of those proteins. We show that CagF is associated to the outer membrane of H. pylori G27 and that the protein is always expressed with electrophoretic mobility variations among the 20 strains tested here. We have also found that natural infection with H. pylori is able to induce antibodies against CagF.

The hppA gene of Helicobacter pylori encodes the class C acid phosphatase precursor

Screening of the Helicobacter pylori genomic library with sera from infected humans and from immunized rabbits resulted in identification of the 25 kDa protein cell envelope (HppA) which exhibits acid phosphatase activity. Enzyme activity was demonstrated by specific enzymatic assays with whole-cell protein preparations of H. pylori strain N6 and from Escherichia coli carrying the hppA gene (pUWM192). HppA showed optimum activity at pH 5.6 and was resistant to inhibition by EDTA. Bioinformatics analysis and site-directed mutagenesis of two putative active site residues (D73 and D192) provide further insight into the sequence-structure-function relationships of HppA as a member of the DDDD phosphohydrolase superfamily.

Identification of surface proteins of Helicobacter pylori by selective biotinylation, affinity purification, and two-dimensional gel electrophoresis

Helicobacter pylori is a widespread human pathogen that can cause gastric ulcers and cancer. To identify surface proteins that may play a role in pathogen-host interactions and represent potential targets for the control of this infection, we selectively biotinylated intact H. pylori with the hydrophilic reagent sulfosuccinimidyl-6-(biotinamido)-hexanoate and purified the labeled proteins by membrane isolation, solubilization, and affinity chromatography. After separation of 82 biotinylated proteins on two-dimensional gels, 18 were identified with comparison to proteome data and peptide mass fingerprinting. Among the identified proteins, 9 have previously been shown to be surface-exposed, 7 are associated with virulence, and 11 are highly immunogenic in infected patients. In conclusion, this generally applicable combined proteome approach facilitates the rapid identification of promising targets for the control of H. pylori and might be applicable to numerous other human pathogens although larger biotinylation reagents might be required in some cases to prevent permeation of porin channels in the outer membrane.

Phase variation in the Helicobacter pylori phospholipase A gene and its role in acid adaptation

Previously, we have shown that Helicobacter pylori can spontaneously and reversibly change its membrane lipid composition, producing variants with low or high content of lysophospholipids. The "lyso" variant contains a high percentage of lysophospholipids, adheres better to epithelial cells, and releases more proteins such as urease and VacA, compared to the "normal" variant, which has a low content of lysophospholipids. Prolonged growth of the normal variant at pH 3.5, but not under neutral conditions, leads to enrichment of lyso variant colonies, suggesting that the colony switch is relevant to acid adaptation. In this study we show that the change in membrane lipid composition is due to phase variation in the pldA gene. A change in the (C) tract length of this gene results in reversible frameshifts, translation of a full-length or truncated pldA, and the production of active or inactive outer membrane phospholipase A (OMPLA). The role of OMPLA in determining the colony morphology was confirmed by the construction of an OMPLA-negative mutant. Furthermore, variants with an active OMPLA were able to survive acidic conditions better than variants with the inactive form. This explains why the lyso variant is selected at low pH. Our studies demonstrate that phase variation in the pldA gene, resulting in an active form of OMPLA, is important for survival under acidic conditions. We also demonstrated the active OMPLA genotype in fresh isolates of H. pylori from patients referred to gastroscopy for dyspepsia.

Polar flagellar motility of the Vibrionaceae

Polar flagella of Vibrio species can rotate at speeds as high as 100,000 rpm and effectively propel the bacteria in liquid as fast as 60 microm/s. The sodium motive force powers rotation of the filament, which acts as a propeller. The filament is complex, composed of multiple subunits, and sheathed by an extension of the cell outer membrane. The regulatory circuitry controlling expression of the polar flagellar genes of members of the Vibrionaceae is different from the peritrichous system of enteric bacteria or the polar system of Caulobacter crescentus. The scheme of gene control is also pertinent to other members of the gamma purple bacteria, in particular to Pseudomonas species. This review uses the framework of the polar flagellar system of Vibrio parahaemolyticus to provide a synthesis of what is known about polar motility systems of the Vibrionaceae. In addition to its propulsive role, the single polar flagellum of V. parahaemolyticus is believed to act as a tactile sensor controlling surface-induced gene expression. Under conditions that impede rotation of the polar flagellum, an alternate, lateral flagellar motility system is induced that enables movement through viscous environments and over surfaces. Although the dual flagellar systems possess no shared structural components and although distinct type III secretion systems direct the simultaneous placement and assembly of polar and lateral organelles, movement is coordinated by shared chemotaxis machinery.

Helicobacter pylori in gastric cancer and peptic ulcer disease in a Colombian population. Strain heterogeneity and antibody profiles

BACKGROUND

Helicobacter pylori infection is associated with peptic ulcer disease and gastric cancer. The aim of this work was to describe, to compare H. pylori antigenic profiles, and to characterize the antibody response against Colombian strains in gastric cancer and peptic ulcer patients.

MATERIALS AND METHODS

Liquid culture supernatants were used to determine the antigenic profiles of 35 H. pylori strains by immunoblotting using a pool of positive sera. Characterization of strains included the evaluation of cytotoxic and vacuolating activities. The serologic antibody profiles of 124 patients (54 duodenal ulcer and 70 gastric cancer) were analyzed against two native strains (Hpu24, Hpc29) and NCTC11638. Antibodies to specific antigenic bands in each strain were related with presentation.

RESULTS

Differences among antigenic profiles were observed between native isolates with each serum recognizing a wide range of antigens (30-120 Kd). A 68 Kd band in Hpu24 strain was recognized by 50% of sera from peptic ulcer patients but not by gastric cancer sera (p =.000). The immune profiles differed according to the strain used (i.e. a given sera did not recognize the same bands in different strains). Detection of H. pylori in gastric mucosa was associated with the presence of antibodies against low molecular weight antigenic bands.

CONCLUSIONS

The heterogeneity in the antibody response to H. pylori and the prevalence specific anti-H. pylori antibodies in a specific disease depend on the strain used as antigen. The results support the hypothesis that there may be a differential antibody response to carcinogenic and ulcerogenic strains and suggest that there are antigenic bands that could be useful as markers of disease.

Natural transformation competence in Helicobacter pylori is mediated by the basic components of a type IV secretion system

Helicobacter pylori (Hp), a Gram-negative bacterial pathogen and aetiologic agent of gastroduodenal disease in humans, is naturally competent for genetic transformation. Natural competence in bacteria is usually correlated with the presence of type IV pili or type IV pilin-like proteins, which are absent in Hp. Instead, we recently identified the comB operon in Hp, carrying four genes tentatively designated as orf2, comB1, comB2 and comB3. We show here that all ComB proteins and the 37-amino-acid Orf2 peptide display significant primary sequence and structural homology/identity to the basic components of a type IV secretion apparatus. ComB1, ComB2 and ComB3, now renamed ComB8, ComB9 and ComB10, correspond to the Agrobacterium tumefaciens VirB8, VirB9 and VirB10 proteins respectively. The peptide Orf2 carries a lipoprotein motif and a second cysteine residue homologous to VirB7, and was thus designated ComB7. The putative ATPase ComB4, encoded by the open reading frame hp0017 of strain 26695, corresponds to virB4 of the A. tumefaciens type IV secretion system. A Hp comB4 transposon insertion mutant was totally defective in natural transformation. By complementation of a Hp DeltacomB deletion mutant, we demonstrate that each of the proteins from ComB8 to ComB10 is absolutely essential for the development of natural transformation competence. The putative lipoprotein ComB7 is not essential, but apparently stabilizes the apparatus and modulates the transformation efficiency. Thus, pathogenic type I Hp strains contain two functional independent type IV transport systems, one for protein translocation encoded by the cag pathogenicity island and one for uptake of DNA by natural transformation. The latter system indicates a possible novel mechanism for natural DNA transformation in bacteria.

Characterization of proteins in the outer membrane preparation of a murine pathogen, Helicobacter bilis

Helicobacter bilis is a bacterial pathogen associated with multifocal hepatitis and inflammatory bowel disease in certain strains of mice. This bacterium colonizes the liver, bile, and lower intestine in mice and has also been isolated from a wide spectrum of laboratory animals. In this study, proteins present in the outer membrane preparation (OMP) of four H. bilis strains isolated from a mouse, a dog, a rat, and a gerbil were characterized and compared with that of Helicobacter pylori, a human gastric pathogen. All four H. bilis strains had similar OMP protein profiles that were distinct from those of H. pylori. Immunoblotting demonstrated that OMP proteins from H. bilis and H. pylori have little cross-reactivity, except for their flagellins. Nine major immunogenic polypeptides were present in the H. bilis OMPs. By using two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, five heat-modifiable proteins with molecular masses of 82, 66, 52, 47 and 37 kDa were identified. The N-terminal sequences of the 46- and 47-kDa OMP proteins had no homology with protein sequences available in public databases. These results indicate that H. bilis has a conserved, unique OMP protein profile that is distinct from those of H. pylori.

Serum immunoglobulin G immune response to Helicobacter pylori antigens in Mongolian gerbils

The Mongolian gerbil model for Helicobacter pylori infection is an animal model that mimics human disease. We examined the serum immune response to H. pylori infection in gerbils by enzyme-linked immunosorbent assay (ELISA) and Western blotting, both with whole-cell (H. pylori) extracts. A total of 66 7-week-old specific-pathogen-free male gerbils were inoculated orogastrically with H. pylori strain ATCC 43504. Sera were collected 1, 2, 4, 8, 12, 26, 38, and 52 weeks after H. pylori inoculation. Sixty-nine noninfected gerbils and their sera were used as controls. The specificity of the ELISA was 95.7%. The frequency of seropositivity increased over time: 2 of 10 (20%), 7 of 10 (70%), and 7 of 7 (100%) samples of sera from inoculated gerbils were positive for H. pylori at 2, 4, and 8 weeks postinoculation, respectively. Western blot assays showed that the primary immunoglobulin G (IgG) response against low-molecular-mass (25-, 30-, and 20-kDa) proteins appeared after a lag period of 2 to 8 weeks after inoculation. Antibodies against 160-, 150-, 110-, 120-, 80-, 66-, and 63-kDa proteins were observed 12 weeks after inoculation. The early reactive 30-kDa protein was identified as a urease alpha subunit by N-terminal amino acid sequencing. After 26 weeks, two groups of animals could be distinguished: one group developed ulcers (n = 5), and the other developed hyperplastic polyps without ulcers (n = 19). Gerbils in the gastric ulcer group showed significantly higher serum anti-H. pylori IgG levels than did gerbils in the hyperplastic group (P = 0.001) as measured by ELISA. Furthermore, a higher proportion of animals developed antibodies to H. pylori proteins of 26, 25, and 20 kDa in the ulcer group than those animals with hyperplastic polyps (75 to 100% versus 17 to 50%) in Western blot assays. These results highlight the importance of the immune response of the host in the development of H. pylori-related gastric lesions.

Differences in surface-exposed antigen expression between Helicobacter pylori strains isolated from duodenal ulcer patients and from asymptomatic subjects

We have analyzed possible qualitative and quantitative differences in antigen expression between Helicobacter pylori strains isolated from the antrum and different locations in the duodenum of 21 duodenal ulcer (DU) patients and 20 asymptomatic subjects (AS) by enzyme-linked immunosorbent assay (ELISA) and inhibition ELISA. Almost all antral and duodenal strains grown in vitro expressed the N-acetyl-neuroaminyllactose-binding hemagglutinin, flagellins (subunits FlaA and FlaB), urease, a 26-kDa protein, and a neutrophil-activating protein. In 75% of both the DU patients and the AS, antral H. pylori strains expressed either the blood group antigen Lewis y (Le(y)) alone or together with the Le(x) antigen. However, duodenal H. pylori strains of DU patients expressed Le(y) antigen more frequently than corresponding strains of AS (P < 0.05). Presence of Le(y) on H. pylori was related to the degree of active duodenitis (P < 0.05). Duodenal H. pylori strains isolated from AS were significantly more often Lewis nontypeable than duodenal strains of DU patients (P < 0.01). Presence of H. pylori blood group antigen-binding adhesin (BabA) was significantly higher on both antral and duodenal strains isolated from DU patients than on corresponding strains isolated from AS (P < 0.05). BabA-positive duodenal H. pylori strains isolated from DU patients were associated with active duodenitis more frequently than corresponding strains isolated from AS (P < 0.01). Infection with H. pylori strains positive for Le(y) and BabA in the duodenum is associated with development of duodenal ulcer formation.

Acid-dependent adherence of Helicobacter pylori urease to diverse polysaccharides

BACKGROUND & AIMS

The significance of acid-primed recognition of ligands by Helicobacter pylori urease is unknown. This study aimed to further characterize the specificity of urease adherence in vitro and verify whether specific inhibition will translate into in vivo suppression of colonization.

METHODS

A highly sensitive competitive enzyme-linked ligand capture assay was used to quantify the capacity of each test inhibitor to compete with labeled mucin for binding sites on immobilized native urease. A model polymer that strongly bound urease was used in an in vivo trial using euthymic hairless mice as an infection model.

RESULTS

The blockage of urease-gastric mucin interaction by certain inhibitors revealed an acid-functional lectin-like activity by urease, specifically recognizing bacterial lipopolysaccharides and certain species of polysaccharides, nonbacterial glycolipids, and glycoproteins. Dextran sulfate significantly (P < 0.01) suppressed colonization of mice by H. pylori when given before and/or after challenge.

CONCLUSIONS

The acid-driven high-affinity adherence of H. pylori urease to mucin and lipopolysaccharides contributes to gastric mucosal colonization by the bacterium based on in vivo targeting experiments using specific polysaccharides in a mouse model with acute infection. Acid-functional urease-homing polysaccharides that can interfere with urease-mucin or H. pylori whole cell-mucin interaction in vitro can significantly interfere with colonization by the bacterium in vivo.