Helicobacter pylori: microbiology of a 'slow' bacterial infection

Helicobacter pylori HP0018 Has a Potential Role in the Maintenance of the Cell Envelope

Helicobacter pylori is a bacterial pathogen that colonizes the human stomach, where it can cause a variety of diseases. H. pylori uses a cluster of sheathed flagella for motility, which is required for host colonization in animal models. The flagellar sheath is continuous with the outer membrane and is found in most Helicobacter species identified to date. HP0018 is a predicted lipoprotein of unknown function that is conserved in Helicobacter species that have flagellar sheaths but is absent in Helicobacter species that have sheath-less flagella. Deletion of hp0018 in H. pylori B128 resulted in the formation of long chains of outer membrane vesicles, which were most evident in an aflagellated variant of the Δhp0018 mutant that had a frameshift mutation in fliP. Flagellated cells of the Δhp0018 mutant possessed what appeared to be a normal flagellar sheath, suggesting that HP0018 is not required for sheath formation. Cells of the Δhp0018 mutant were also less helical in shape compared to wild-type cells. A HP0018-superfolder green fluorescent fusion protein expressed in the H. pylori Δhp0018 mutant formed fluorescent foci at the cell poles and lateral sites. Co-immunoprecipitation assays with HP0018 identified two enzymes involved in the modification of the cell wall peptidoglycan, AmiA and MltD, as potential HP0018 interaction partners. HP0018 may modulate the activity of AmiA or MltD, and in the absence of HP0018, the unregulated activity of these enzymes may alter the peptidoglycan layer in a manner that results in an altered cell shape and hypervesiculation.

A Multi-Omics Study on the Effect of Helicobacter Pylori-Related Genes in the Tumor Immunity on Stomach Adenocarcinoma

Background

Helicobacter pylori (HP), a gram-negative spiral-shaped microaerophilic bacterium, colonizes the stomach of approximately 50% of the world’s population, which is considered a risk factor for gastritis, peptic ulcers, gastric cancer, and other malignancies. HP is also considered carcinogenic since it involves the mutation and damage of multiple HP-related genes. Stomach adenocarcinoma (STAD) is a common stom5ach cancer with a poor prognosis and high risk of metastasis in the advanced stage. Therefore, an early diagnosis and targeted therapies are needed to ensure a better prognosis. In this study, a scoring system was constructed based on three HP infection–related candidate genes to enable a more accurate prediction of tumor progression and metastasis and response to immunotherapies.

Methods

HP infection–induced mutation patterns of STAD samples from six cohorts were comprehensively assessed based on 73 HP-related genes, which were then correlated with the immune cell–infiltrating characteristics of the tumor microenvironment (TME). The risk signature was constructed to quantify the influence of HP infection on individual tumors. Subsequently, an accurate nomogram was generated to improve the clinical applicability of the risk signature. We conducted immunohistochemical experiments and used the Affiliated Hospital of Youjiang Medical University for Nationalities (AHYMUN) cohort data set with survival information to further verify the clinical value of this risk signature.

Results

Two distinct HP-related mutation patterns with different immune cell–infiltrating characteristics (ICIC) and survival possibility were identified. We demonstrated that the evaluation of HP infection–induced mutation patterns of tumor could assist the prediction of stages, phenotypes, stromal activity, genetic diversity, and patient prognosis. A low risk score involved an increased mutation burden and activation of immune responses, with a higher 5-year survival rate and enhanced response to anti-PD-1/L1 immunotherapy, while a high risk score involved stromal activation and poorer survival. The efficiency of the risk signature was further evidenced by the nomogram.

Conclusions

STAD patients with a low risk score demonstrated significant therapeutic advantages and clinical benefits. HP infection–induced mutations play a nonnegligible role in STAD development. Quantifying the HP-related mutation patterns of individual tumors will contribute to phenotype classification, guide more effective targeted and personalized therapies, and enable more accurate predictions of metastasis and prognosis.

Methylation Motifs in Promoter Sequences May Contribute to the Maintenance of a Conserved m5C Methyltransferase in Helicobacter pylori

DNA methylomes of Helicobacter pylori strains are complex due to the large number of DNA methyltransferases (MTases) they possess. H. pylori J99 M.Hpy99III is a 5-methylcytosine (^m5C) MTase that converts GCGC motifs to G^m5CGC. Homologs of M.Hpy99III are found in essentially all H. pylori strains. Most of these homologs are orphan MTases that lack a cognate restriction endonuclease, and their retention in H. pylori strains suggest they have roles in gene regulation. To address this hypothesis, green fluorescent protein (GFP) reporter genes were constructed with six putative promoters that had a GCGC motif in the extended −10 region, and the expression of the reporter genes was compared in wild-type H. pylori G27 and a mutant lacking the M.Hpy99III homolog (M.HpyGIII). The expression of three of the GFP reporter genes was decreased significantly in the mutant lacking M.HpyGIII. In addition, the growth rate of the H. pylori G27 mutant lacking M.HpyGIII was reduced markedly compared to that of the wild type. These findings suggest that the methylation of the GCGC motif in many H. pylori GCGC-containing promoters is required for the robust expression of genes controlled by these promoters, which may account for the universal retention of M.Hpy99III homologs in H. pylori strains.

Loss of a Cardiolipin Synthase in Helicobacter pylori G27 Blocks Flagellum Assembly

Helicobacter pylori uses a cluster of polar, sheathed flagella for motility, which it requires for colonization of the gastric epithelium in humans. As part of a study to identify factors that contribute to localization of the flagella to the cell pole, we disrupted a gene encoding a cardiolipin synthase (clsC) in H. pylori strains G27 and B128. Flagellum biosynthesis was abolished in the H. pylori G27 clsC mutant but not in the B128 clsC mutant. Transcriptome sequencing analysis showed that flagellar genes encoding proteins needed early in flagellum assembly were expressed at wild-type levels in the G27 clsC mutant. Examination of the G27 clsC mutant by cryo-electron tomography indicated the mutant assembled nascent flagella that contained the MS ring, C ring, flagellar protein export apparatus, and proximal rod. Motile variants of the G27 clsC mutant were isolated after allelic exchange mutagenesis using genomic DNA from the B128 clsC mutant as the donor. Genome resequencing of seven motile G27 clsC recipients revealed that each isolate contained the flgI (encodes the P-ring protein) allele from B128. Replacing the flgI allele in the G27 clsC mutant with the B128 flgI allele rescued flagellum biosynthesis. We postulate that H. pylori G27 FlgI fails to form the P ring when cardiolipin levels in the cell envelope are low, which blocks flagellum assembly at this point. In contrast, H. pylori B128 FlgI can form the P ring when cardiolipin levels are low and allows for the biosynthesis of mature flagella.IMPORTANCE H. pylori colonizes the epithelial layer of the human stomach, where it can cause a variety of diseases, including chronic gastritis, peptic ulcer disease, and gastric cancer. To colonize the stomach, H. pylori must penetrate the viscous mucous layer lining the stomach, which it accomplishes using its flagella. The significance of our research is identifying factors that affect the biosynthesis and assembly of the H. pylori flagellum, which will contribute to our understanding of motility in H. pylori, as well as other bacterial pathogens that use their flagella for host colonization.

Prokaryotic and Mitochondrial Lipids: A Survey of Evolutionary Origins

Mitochondria and bacteria share a myriad of properties since it is believed that the powerhouses of the eukaryotic cell have evolved from a prokaryotic origin. Ribosomal RNA sequences, DNA architecture and metabolism are strikingly similar in these two entities. Proteins and nucleic acids have been a hallmark for comparison between mitochondria and prokaryotes. In this chapter, similarities (and differences) between mitochondrial and prokaryotic membranes are addressed with a focus on structure-function relationship of different lipid classes. In order to be suitable for the theme of the book, a special emphasis is reserved to the effects of bioactive sphingolipids, mainly ceramide, on mitochondrial membranes and their roles in initiating programmed cell death.

Inhibition of bacterial toxin recognition of membrane components as an anti-virulence strategy

Over recent years, the development of new antibiotics has not kept pace with the rate at which bacteria develop resistance to these drugs. For this reason, many research groups have begun to design and study alternative therapeutics, including molecules to specifically inhibit the virulence of pathogenic bacteria. Because many of these pathogenic bacteria release protein toxins, which cause or exacerbate disease, inhibition of the activity of bacterial toxins is a promising anti-virulence strategy. In this review, we describe several approaches to inhibit the initial interactions of bacterial toxins with host cell membrane components. The mechanisms by which toxins interact with the host cell membrane components have been well-studied over the years, leading to the identification of therapeutic targets, which have been exploited in the work described here. We review efforts to inhibit binding to protein receptors and essential membrane lipid components, complex assembly, and pore formation. Although none of these molecules have yet been demonstrated in clinical trials, the in vitro and in vivo results presented here demonstrate their promise as novel alternatives and/or complements to traditional antibiotics.

The Gastric and Intestinal Microbiome: Role of Proton Pump Inhibitors

PURPOSE OF REVIEW

The discovery of Helicobacter pylori and other organisms colonizing the stomach and the intestines has shed some light on the importance of microbiome in maintaining overall health and developing pathological conditions when alterations in biodiversity are present. The gastric acidity plays a crucial role in filtering out bacteria and preventing development of enteric infections. In this article, we discuss the physiology of gastric acid secretion and bacterial contribution to the composition of gastric and intestinal barriers and review the current literature on the role of proton pump inhibitors (PPIs) in the microbial biodiversity of the gastrointestinal tract.

RECENT FINDINGS

Culture-independent techniques, such as 16S rRNA sequencing, have revolutionized our understanding of the microbial biodiversity in the gastrointestinal tract. Luminal and mucosa-associated microbial populations are not identical. Streptococcus is overrepresented in the biopsies of patients with antral gastritis and may also be responsible for the development of peptic ulcer disease. The use of PPIs favors relative streptococcal abundance irrespective of H. pylori status and may explain the persistence of dyspeptic symptoms in patients on PPI therapy. Increased risk of enteric infections has also been seen in patients taking PPIs. The overuse of PPIs leads to significant shift of the gastrointestinal microbiome towards a less healthy state. With the advent of PPIs, many studies have demonstrated the significant changes in the microbial composition of both gastric and intestinal microbiota. Although they are considered relatively safe over-the-counter medications, PPIs in many cases are over- and even inappropriately used. Future studies assessing the safety of PPIs and their role in the development of microbiome changes should be encouraged.

Host pathogen interactions in Helicobacter pylori related gastric cancer

Helicobacter pylori (H. pylori), discovered in 1982, is a microaerophilic, spiral-shaped gram-negative bacterium that is able to colonize the human stomach. Nearly half of the world's population is infected by this pathogen. Its ability to induce gastritis, peptic ulcers, gastric cancer and mucosa-associated lymphoid tissue lymphoma has been confirmed. The susceptibility of an individual to these clinical outcomes is multifactorial and depends on H. pylori virulence, environmental factors, the genetic susceptibility of the host and the reactivity of the host immune system. Despite the host immune response, H. pylori infection can be difficult to eradicate. H. pylori is categorized as a group I carcinogen since this bacterium is responsible for the highest rate of cancer-related deaths worldwide. Early detection of cancer can be lifesaving. The 5-year survival rate for gastric cancer patients diagnosed in the early stages is nearly 90%. Gastric cancer is asymptomatic in the early stages but always progresses over time and begins to cause symptoms when untreated. In 97% of stomach cancer cases, cancer cells metastasize to other organs. H. pylori infection is responsible for nearly 60% of the intestinal-type gastric cancer cases but also influences the development of diffuse gastric cancer. The host genetic susceptibility depends on polymorphisms of genes involved in H. pylori-related inflammation and the cytokine response of gastric epithelial and immune cells. H. pylori strains differ in their ability to induce a deleterious inflammatory response. H. pylori-driven cytokines accelerate the inflammatory response and promote malignancy. Chronic H. pylori infection induces genetic instability in gastric epithelial cells and affects the DNA damage repair systems. Therefore, H. pylori infection should always be considered a pro-cancerous factor.

Activity in the Limulus amebocyte lysate assay and induction of tumor necrosis factor-α by diverse Helicobacter pylori lipopolysaccharide preparations

Different chemically characterized H. pylori LPS preparations, such as smooth (S)- and rough (R)-form LPS, a completely dephosphorylated R-LPS, and three lipid A chemotypes, from the S- and R- form LPS (S- and R-lipid A) as well as a dephosphorylated derivative of S-lipid A, respectively, were evaluated for expression of potency in a quantitative chromogenic Limulus amebocyte (CLAL) lysate assay and for release of tumor necrosis factor-α (TNF-α) from activated human mononuclear cells. As far as the CLAL activity is concerned, no statistically significant differences could be observed between S- and R-LPS. Dephosphorylation of both R-LPS and S-lipid A caused a significant decrease of CLAL activity. In general terms, all the lipid A chemotypes were significantly less effective than the native LPS molecule and, in particular, R-lipid A expressed the lowest Limulus activity of all preparations. With regard to TNF-α release, R-LPS was the most potent inducer of this cytokine, even though its dephosphorylation reduced activity. In conclusion, the results show that phosphate groups influence both CLAL activity and, to a lesser extent, TNF-α release, and that the core oligosaccharide synergically cooperates with lipid A for the production of this cytokine, being, however, not essential for the expression of CLAL activity. Furthermore, preliminary structural data show that H. pylori D-glucosamine disaccharide backbone, besides being underphosphorylated at position 4', is also characterized by a reduced number of acyloxyacyl residues in comparison with enterobacterial lipid A. These findings, besides providing useful information on the structure-bioactivity relationships within H. pylori LPS, further support the evidence that this non-invasive, slow bacterium possesses the ability to modulate the local cellular immune response via LPS and related inflammatory cytokines.

Helicobacter pylori FlhA Binds the Sensor Kinase and Flagellar Gene Regulatory Protein FlgS with High Affinity

Flagellar biogenesis is a complex process that involves multiple checkpoints to coordinate transcription of flagellar genes with the assembly of the flagellum. In Helicobacter pylori, transcription of the genes needed in the middle stage of flagellar biogenesis is governed by RpoN and the two-component system consisting of the histidine kinase FlgS and response regulator FlgR. In response to an unknown signal, FlgS autophosphorylates and transfers the phosphate to FlgR, initiating transcription from RpoN-dependent promoters. In the present study, export apparatus protein FlhA was examined as a potential signal protein. Deletion of its N-terminal cytoplasmic sequence dramatically decreased expression of two RpoN-dependent genes, flaB and flgE. Optical biosensing demonstrated a high-affinity interaction between FlgS and a peptide consisting of residues 1 to 25 of FlhA (FlhANT). The KD (equilibrium dissociation constant) was 21 nM and was characterized by fast-on (kon = 2.9 × 10(4) M(-1)s(-1)) and slow-off (koff = 6.2 × 10(-4) s(-1)) kinetics. FlgS did not bind peptides consisting of smaller fragments of the FlhANT sequence. Analysis of binding to purified fragments of FlgS demonstrated that the C-terminal portion of the protein containing the kinase domain binds FlhANT. FlhANT binding did not stimulate FlgS autophosphorylation in vitro, suggesting that FlhA facilitates interactions between FlgS and other structures required to stimulate autophosphorylation.

IMPORTANCE

The high-affinity binding of FlgS to FlhA characterized in this study points to an additional role for FlhA in flagellar assembly. Beyond its necessity for type III secretion, the N-terminal cytoplasmic sequence of FlhA is required for RpoN-dependent gene expression via interaction with the C-terminal kinase domain of FlgS.

Does a relationship still exist between gastroesophageal reflux and Helicobacter pylori in patients with reflux symptoms?

Background

The nature of the relationship between Helicobacter pylori and reflux esophagitis (RE) is not fully understood. In addition, the effect of H. pylori eradication on RE and gastroesophageal reflux disease (GERD) is unclear. This study was designed to investigate the relationship between H. pylori infection and the grade of GERD in patients with reflux symptoms.

Methods

Between January 2010 and July 2013, 184 consecutive patients with daily reflux symptoms for at least one year were evaluated at the ambulatory for functional esophageal disease, Tor Vergata University Hospital, Rome, Italy. All patients underwent a pretreatment evaluation, which included anamnesis, clinical examination, Esophagogastroduodenoscopy (EGDS) with biopsy, esophageal manometry and 24-hour pH-metry. All statistical elaborations were obtained using Statigraphies 5 plus for Window XP.

Results

There was no statistical difference regarding Lower Esophageal Sphincter (LES) pressure between patients who were H. pylori-positive and H. Pylori-negative (19.2 ± 9.5 (range: 3.7 to 46.2) and 19.7 ± 11.0 (range: 2.6 to 61), respectively). Further, no significant difference was evidenced in esophageal wave length (mean value: 3.1 seconds in H. pylori-negative patients versus 3.2 seconds in H. pylori-positive patients) or in esophageal wave height (mean value: 72.2 ± 39.3 in H. pylori-negative patients versus 67.7 ± 28.4 in H. pylori-positive patients). We observed that hiatal hernia (P = 0.01), LES opening (P = 0.05), esophageal wave length (P = 0.01) and pathological reflux number (P = 0.05) were significantly related to the presence of esophagitis. However, H. pylori infection was not significantly related to the presence of reflux esophagitis.

Conclusions

Our clinical, endoscopic, manometric and pH-metric data shows no significant role of H. pylori infection in the development of GERD or in the pathogenesis of reflux esophagitis. However, current data do not provide sufficient evidence to define this relationship and further prospective large studies are needed.

Evaluation of Helicobacter pylori vacA and cagA Genotypes and Correlation With Clinical Outcome in Patients With Dyspepsia in Hamadan Province, Iran

Background:

Helicobacter pylori is known to be a causative agent of chronic active gastritis, peptic ulcer and gastric cancer in human. Diverse genotypes of H. pylori strains have different virulence potency and geographic distribution.

Objectives:

The purpose of this study was to investigate the association between the cytotoxin-associated gene (cagA), and the various vacuolating cytotoxin (vacA) genotypes of H. pylori strains and clinical outcomes in patients referred to Shahid-Beheshti Hospital in Hamadan, Iran.

Patients and Methods:

In this cross-sectional study, biopsy samples were collected consecutively from 153 patients with gastric cancer (GC), peptic ulcer dyspepsia (PUD) and non-ulcer dyspepsia (NUD) in the gastroenterology department of Shahid-Beheshti Hospital in Hamadan province, the west of Iran. H. pylori infection was confirmed in 83 patients (3 with GC, 27 with PUD, and 53 with NUD) by histology, rapid urease test (RUT) and culture. Genomic DNA was extracted from the bacterial isolate and was further confirmed with 16S rRNA gene sequencing as H. pylori, and characterized based on cagA and vacA genotyping using the polymerase chain reaction (PCR) method.

Results:

In this study, vacA genotypes s1/m2, s1/m1, s2/m2 and s2/m1 were determined in 43.4%, 19.3%, 13.2% and 6% of the isolated H. pylori, respectively. The vacAs1 genotype was detected in 52 (62.6%) isolates, of which the vacAs1a genotype was detected in 45.2, 40.7, and 66.6% of the isolates from patients with NUD, PUD, and GC, respectively. The cagA-positive genotype was determined in 73 (87.9%) isolates and 10 (12.1%) were negative. The frequency rates of cagA gene were 84.9, 92.6 and 100% in isolates of patients with NUD, PUD, and GC, respectively. The cagA-positive genotype is strongly associated with s1a/m2 and s1a/m1 vacA genotypes.

Conclusions:

The most predominant VacA genotypes in our areas were s1/m2 and s1/m1, which regard as the genotypes with more virulence intensity. The H. pylorivacAs1a, cagA genotypes have a significant relationship with the presence of PUD and GC in Iranian patients with dyspepsia.

Vector-encoded Helicobacter pylori neutrophil-activating protein promotes maturation of dendritic cells with Th1 polarization and improved migration

Helicobacter pylori neutrophil-activating protein (HP-NAP) is a major virulence factor involved in H. pylori infection. Both HP-NAP protein and oncolytic viruses encoding HP-NAP have been suggested as immunotherapeutic anticancer agents and adjuvants for vaccination but with little known about its mode of action to activate adaptive immunity. Dendritic cells (DCs) are key players in bridging innate and adaptive immune responses, and in this study we aim to evaluate the effect of HP-NAP on DC maturation, migration, and induction of adaptive immune response. Maturation markers CD83, CD80, CD86, HLA-DR, CD40, and CCR7 were upregulated on human DCs after treatment with supernatants from HP-NAP adenovirus-infected cells. HP-NAP-activated DCs had a Th1 cytokine secretion profile, with high IL-12 and relatively low IL-10 secretion, and migrated toward CCL19. Ag-specific T cells were efficiently expanded by Ag-presenting HP-NAP-activated DCs, which is an important property of functionally mature DCs. Furthermore, intradermal injections of HP-NAP-encoding adenovirus in C57BL/6 mice enhanced resident DC migration to draining lymph nodes, which was verified by imaging lymph nodes by two-photon microscopy and by phenotyping migrating cells by flow cytometry. In conclusion, therapeutic effects of HP-NAP are mediated by maturation of DCs and subsequent activation of Ag-specific T cells in addition to provoking innate immunity.

Requirement of the flagellar protein export apparatus component FliO for optimal expression of flagellar genes in Helicobacter pylori

Flagellar biogenesis in Helicobacter pylori involves the coordinated expression of flagellar genes with assembly of the flagellum. The H. pylori flagellar genes are organized into three regulons based on the sigma factor needed for their transcription (RpoD [σ(80)], RpoN [σ(54)], or FliA [σ(28)]). Transcription of RpoN-dependent genes is activated by a two-component system consisting of the sensor kinase FlgS and the response regulator FlgR. While the cellular cues sensed by the FlgS/FlgR two-component system remain to be elucidated, previous studies revealed that disrupting certain components of the flagellar export apparatus inhibited transcription of the RpoN regulon. FliO is the least conserved of the membrane-bound components of the export apparatus and has not been annotated for any of the H. pylori genomes sequenced to date. A PSI-BLAST analysis identified a potential H. pylori FliO protein which membrane topology algorithms predict to possess a large N-terminal periplasmic domain that is absent from FliO of Escherichia coli and Salmonella, the paradigms for flagellar structure/function studies. FliO was necessary for flagellar biogenesis as well as wild-type levels of motility and transcription of RpoN-dependent and FliA-dependent flagellar genes in H. pylori strain B128. FliO also appears to be required for wild-type levels of the export apparatus protein FlhA in the membrane. Interestingly, the periplasmic and cytoplasmic domains were somewhat dispensable for flagellar gene regulation and assembly, suggesting that these domains have relatively minor roles in flagellar synthesis.

Antimicrobial and anti-inflammatory properties of Funtumia elastica

CONTEXT

Funtumia elastica (Preuss) Stapf. (Apocynaceae) has a long ethnopharmacological history for uses such as treatment of whooping cough, asthma, blennorhea, painful menstruation, fungal infections, and wounds.

OBJECTIVE

To investigate the antimicrobial and anti-inflammatory properties of ethanol extracts from the leaves and stem bark of Funtumia elastica based on its ethnopharmacological uses and also determine the secondary metabolites present in the extracts.

MATERIALS AND METHODS

The antimicrobial activities of ethanol leaf and bark extracts of F. elastica were determined using the microdilution technique (MIC determination) and agar diffusion method using 10, 25, and 50 mg/mL concentrations against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Candida albicans, Aspergillus flavus and Aspergillus niger as test organisms. Anti-inflammatory activities of the doses of extracts at 30, 100, and 300 mg/kg per body weight were determined by carrageenan-induced edema in the footpad of 7-day-old chicks and the foot volumes measured at hourly interval post-treatment for 5 h.

RESULTS

The MIC ranges of both ethanol leaf and bark extracts against the test organisms were 125 (lowest MIC) to 1550 µg/mL (highest MIC) and 125 (lowest MIC) to 1750 µg/mL (highest MIC), respectively. The ethanol leaf and bark extract of F. elastica showed significant anti-inflammatory activity (p ≤ 0.001) at 30, 100 and 300 mg/kg. Preliminary phytochemical screening revealed that F. elastica bark contains hydrolysable tannins, sapogenetic glycosides, steroids and saponins while the leaves contain hydrolysable tannins, flavonoids, starch and alkaloids. Tannin contents of the leaf and stem bark were 2.4 and 1.3% w/w (related to the dried material), respectively.

DISCUSSION AND CONCLUSION

Both ethanol leaf and bark extracts of F. elastica showed antimicrobial and anti-inflammatory activities and these pharmacological properties may be responsible for the ethnomedicinal uses of the leaves and stem bark of the plant.

Prevalence of Helicobacter pylori infection and the incidence of ureA and clarithromycin resistance gene 23S rRNA genotypes status in Saudi Arabia

OBJECTIVES

To determine the prevalence of Helicobacter pylori ureA and clarithromycin resistance gene 23S rRNA genotypes among H. pylori in Saudi Arabia.

METHODS

A total of 100 serum and fecal samples from 70 patients and 30 healthy volunteers, from patients who presented with symptoms suggestive of gastritis or peptic ulcer disease, were taken from the main hospital in the Southern region of Saudi Arabia from September 2010 C.E. to March 2011 C.E. corresponding to Shawwal 1431 A.H. to Rabi Al-Thani 1432 A.H. We cultured the samples for H. pylori and a polymerase chain reaction was carried out to check for the presence or absence of ureA gene and clarithromycin resistance gene 23S rRNA genotypes.

RESULTS

Among the 70 suspected patients, the suspected bacteria isolated from the fecal samples of 60, (85.7%) were positive using the culture techniques. The presence of ureA gene and clarithromycin resistance gene 23S rRNA was determined by using the polymerase chain reaction, Among the 100 fecal specimens, 65 fecal specimens from 70% patients showed positive results to clarithromycin resistance gene 23S rRNA (sensitivity, 93%; Specificity, 100% and Accuracy, 95%), Only 60 fecal specimens were positive with ureA gene (sensitivity, 86%; Specificity, 100% and Accuracy, 90%).

CONCLUSION

23S rRNA gene was associated with clarithromycin resistance in H. pylori. There was a high prevalence of H. pylori resistance to clarithromycin in Saudi Arabia. H. pylori is a neutrophilic bacteria that has been able to colonize the human stomach by using a variety of acid-adaptive mechanisms as Urease activity that hydrolyzed the Urea producing 2 NH3 and H2CO3.

Insertion mutations in Helicobacter pylori flhA reveal strain differences in RpoN-dependent gene expression

Flagellar biogenesis in the gastric pathogen Helicobacter pylori involves a transcriptional hierarchy that utilizes all three sigma factors found in this bacterium (RpoD, RpoN and FliA). Transcription of the RpoN-dependent genes requires the sensor kinase FlgS and response regulator FlgR. It is thought that FlgS senses some cellular cue to regulate transcription of the RpoN-dependent flagellar genes, but this signal has yet to be identified. Previous studies showed that transcription of the RpoN-dependent genes is inhibited by mutations in flhA, which encodes a membrane-bound component of the flagellar protein export apparatus. We found that depending on the H. pylori strain used, insertion mutations in flhA had different effects on expression of RpoN-dependent genes. Mutations in flhA in H. pylori strains B128 and ATCC 43504 (the type strain) were generated by inserting a chloramphenicol resistance cassette so as to effectively eliminate expression of the gene (ΔflhA), or within the gene following codon 77 (designated flhA77) or codon 454 (designated flhA454), which could allow expression of truncated FlhA proteins. All three flhA mutations severely inhibited transcription of the RpoN-dependent genes flaB and flgE in H. pylori B128. In contrast, levels of flaB and flgE transcripts in H. pylori ATCC 43504 bearing either flhA77 or flhA454, but not ΔflhA, were ~60 % of wild-type levels. The FlhA(454) variant was detected in membrane fractions prepared from H. pylori ATCC 43504 but not H. pylori B128, which may account for the phenotypic differences in the flhA mutations of the two strains. Taken together, these findings suggest that only the N-terminal region of FlhA is needed for transcription of the RpoN regulon. Interestingly, expression of an flaB'-'xylE reporter gene in H. pylori ATCC 43504 bearing the flhA77 allele was about eightfold higher than that of a strain with the wild-type allele, suggesting that expression of flaB is not only regulated at the level of transcription but also regulated post-transcriptionally.

Fut2-null mice display an altered glycosylation profile and impaired BabA-mediated Helicobacter pylori adhesion to gastric mucosa

Glycoconjugates expressed on gastric mucosa play a crucial role in host-pathogen interactions. The FUT2 enzyme catalyzes the addition of terminal alpha(1,2)fucose residues, producing the H type 1 structure expressed on the surface of epithelial cells and in mucosal secretions of secretor individuals. Inactivating mutations in the human FUT2 gene are associated with reduced susceptibility to Helicobacter pylori infection. H. pylori infects over half the world's population and causes diverse gastric lesions, from gastritis to gastric cancer. H. pylori adhesion constitutes a crucial step in the establishment of a successful infection. The BabA adhesin binds the Le(b) and H type 1 structures expressed on gastric mucins, while SabA binds to sialylated carbohydrates mediating the adherence to inflamed gastric mucosa. In this study, we have used an animal model of nonsecretors, Fut2-null mice, to characterize the glycosylation profile and evaluate the effect of the observed glycan expression modifications in the process of H. pylori adhesion. We have demonstrated expression of terminal difucosylated glycan structures in C57Bl/6 mice gastric mucosa and that Fut2-null mice showed marked alteration in gastric mucosa glycosylation, characterized by diminished expression of alpha(1,2)fucosylated structures as indicated by lectin and antibody staining and further confirmed by mass spectrometry analysis. This altered glycosylation profile was further confirmed by the absence of Fucalpha(1,2)-dependent binding of calicivirus virus-like particles. Finally, using a panel of H. pylori strains, with different adhesin expression profiles, we have demonstated an impairment of BabA-dependent adhesion of H. pylori to Fut2-null mice gastric mucosa, whereas SabA-mediated binding was not affected.

Association of anti-Helicobacter pylori neutrophil-activating protein antibody response with anti-aquaporin-4 autoimmunity in Japanese patients with multiple sclerosis and neuromyelitis optica

There are two distinct subtypes of multiple sclerosis (MS) in Asians: opticospinal (OSMS) and conventional (CMS). OSMS has similar features to neuromyelitis optica (NMO) and half of OSMS patients have the NMO-Immunoglobulin G (IgG)/ anti-aquaporin-4 (AQP4) antibody. We reported that Helicobacter pylori (H. pylori) infection was significantly less common in CMS patients than controls. To reveal the immune responses to the H. pylori neutrophil-activating protein (HP-NAP) in Japanese MS patients, according to anti-AQP4 antibody status, sera from 162 MS patients, 37 patients with other inflammatory neurological diseases (OIND), and 85 healthy subjects were assayed for anti-H. pylori antibodies, anti-HP-NAP antibodies, and myeloperoxidase (MPO) by enzyme immunoassays. H. pylori seropositivity rates were significantly higher in anti-AQP4 antibody-positive MS/NMO (AQP4 + /MS) patients (19/27, 70.4%) than anti-AQP4 antibody-negative CMS (AQP4 - /CMS) patients (22/83, 26.5%). Among H. pylori-infected individuals, the anti-HP-NAP antibody was significantly more common in AQP4 + /MS and AQP4 - /OSMS patients than healthy subjects (36.8%, 34.6% versus 2.8%). Among the AQP4 + /MS patients, a significant positive correlation between anti-HP-NAP antibody levels and the final Kurtzke's Expanded Disability Status Scale scores was found, and MPO levels were higher in anti-HP-NAP antibody-positive patients than anti-HP-NAP antibody-negative ones. Therefore, HP-NAP may be associated with the pathology of anti-AQP4 antibody-related neural damage in MS/NMO patients.

Helicobacter pylori, asthma and allergy

Bronchial asthma and allergic diseases are orchestrated by T-cells producing T-helper type 2 (Th2) cytokines, such as interleukin-4 (IL-4) and IL-5, and are inhibited by Th1 responses. Helicobacter pylori has chronically infected the human population for c. 100,000 years and preferentially elicits a Th1 mucosal immune response with the production of interferon-gamma and IL-12. Among several bacterial factors, the neutrophil-activating protein of H. pylori (HP-NAP) not only plays a key role in driving Th1 inflammation but it is also able to inhibit Th2 responses in vitro and in vivo in allergic bronchial asthma, in humans and mice. Both systemic and mucosal administrations of HP-NAP are successful in reducing eosinophilia, immunoglobulin E and systemic Th2 cytokines at the bronchial level. Thus, these results identify HP-NAP as a candidate for novel strategies for the prevention and treatment of allergic diseases.

Helicobacter pylori and gastroesophageal reflux disease

BACKGROUND

The nature of the relationship between Helicobacter pylori and reflux oesophagitis is still not clear. To investigate the correlation between Helicobacter pylori infection and GERD taking into account endoscopic, pH-metric and histopathological data.

METHODS

Between January 2001 and January 2003 a prospective study was performed in 146 patients with GERD in order to determine the prevalence of Helicobacter pylori infection at gastric mucosa; further the value of the De Meester score endoscopic, manometric and pH-metric parameters, i.e. reflux episodes, pathological reflux episodes and extent of oesophageal acid exposure, of the patients with and without Helicobacter pylori infection were studied and statistically compared. Finally, univariate analysis of the above mentioned data were performed in order to evaluate the statistical correlation with reflux esophagitis.

RESULTS

There were no statistically significant differences between the two groups, HP infected and HP negative patients, regarding age, gender and type of symptoms. There was no statistical difference between the two groups regarding severity of symptoms and manometric parameters. The value of the De Meester score and the ph-metric parameters were similar in both groups. On univariate analysis, we observed that hiatal hernia (p = 0,01), LES size (p = 0,05), oesophageal wave length (p = 0,01) and pathological reflux number (p = 0,05) were significantly related to the presence of reflux oesophagitis.

CONCLUSION

Based on these findings, it seems that there is no significant evidence for an important role for H. pylori infection in the development of GERD and erosive esophagitis. Nevertheless, current data do not provide sufficient evidence to define the relationship between HP and GERD. Further assessments in prospective large studies are warranted.

The human gastric pathogen Helicobacter pylori has a potential acetone carboxylase that enhances its ability to colonize mice

Background

Helicobacter pylori colonizes the human stomach and is the etiological agent of peptic ulcer disease. All three H. pylori strains that have been sequenced to date contain a potential operon whose products share homology with the subunits of acetone carboxylase (encoded by acxABC) from Xanthobacter autotrophicus strain Py2 and Rhodobacter capsulatus strain B10. Acetone carboxylase catalyzes the conversion of acetone to acetoacetate. Genes upstream of the putative acxABC operon encode enzymes that convert acetoacetate to acetoacetyl-CoA, which is metabolized further to generate two molecules of acetyl-CoA.

Results

To determine if the H. pylori acxABC operon has a role in host colonization the acxB homolog in the mouse-adapted H. pylori SS1 strain was inactivated with a chloramphenicol-resistance (cat) cassette. In mouse colonization studies the numbers of H. pylori recovered from mice inoculated with the acxB:cat mutant were generally one to two orders of magnitude lower than those recovered from mice inoculated with the parental strain. A statistical analysis of the data using a Wilcoxin Rank test indicated the differences in the numbers of H. pylori isolated from mice inoculated with the two strains were significant at the 99% confidence level. Levels of acetone associated with gastric tissue removed from uninfected mice were measured and found to range from 10–110 μmols per gram wet weight tissue.

Conclusion

The colonization defect of the acxB:cat mutant suggests a role for the acxABC operon in survival of the bacterium in the stomach. Products of the H. pylori acxABC operon may function primarily in acetone utilization or may catalyze a related reaction that is important for survival or growth in the host. H. pylori encounters significant levels of acetone in the stomach which it could use as a potential electron donor for microaerobic respiration.

The Helicobacter pylori's protein VacA has direct effects on the regulation of cell cycle and apoptosis in gastric epithelial cells

In this study, we have evaluated the effects on cell cycle regulation of VacA alone and in combination with other two Helicobacter pylori proteins, cytotoxin-associated protein (CagA) and HspB, using the human gastric epithelial cells (AGS). Our results indicate that VacA alone was able to inhibit the G1 to S progression of the cell cycle. The VacA capacity of inhibiting cell progression from G1 to S phase was also observed when cells were co-transfected with CagA or HspB. Moreover, VacA over-expression caused apoptosis in AGS cells through activation of caspase 8 and even more of caspase 9, thus indicating an involvement of both the receptor-mediated and the mitochondrial pathways of apoptosis. Indeed, the two pathways probably can co-operate to execute cell death with a prevalence of the mitochondrial pathways. Our data taken together provide additional information to further enhance our understanding of the molecular mechanism by which H. pylori proteins alter the growth status of human gastric epithelial cells.

Helicobacter pylori evolution: lineage- specific adaptations in homologs of eukaryotic Sel1-like genes

Geographic partitioning is postulated to foster divergence of Helicobacter pylori populations as an adaptive response to local differences in predominant host physiology. H. pylori's ability to establish persistent infection despite host inflammatory responses likely involves active management of host defenses using bacterial proteins that may themselves be targets for adaptive evolution. Sequenced H. pylori genomes encode a family of eight or nine secreted proteins containing repeat motifs that are characteristic of the eukaryotic Sel1 regulatory protein, whereas the related Campylobacter and Wolinella genomes each contain only one or two such "Sel1-like repeat" (SLR) genes ("slr genes"). Signatures of positive selection (ratio of nonsynonymous to synonymous mutations, dN/dS = omega > 1) were evident in the evolutionary history of H. pylori slr gene family expansion. Sequence analysis of six of these slr genes (hp0160, hp0211, hp0235, hp0519, hp0628, and hp1117) from representative East Asian, European, and African H. pylori strains revealed that all but hp0628 had undergone positive selection, with different amino acids often selected in different regions. Most striking was a divergence of Japanese and Korean alleles of hp0519, with Japanese alleles having undergone particularly strong positive selection (omegaJ > 25), whereas alleles of other genes from these populations were intermingled. Homology-based structural modeling localized most residues under positive selection to SLR protein surfaces. Rapid evolution of certain slr genes in specific H. pylori lineages suggests a model of adaptive change driven by selection for fine-tuning of host responses, and facilitated by geographic isolation. Characterization of such local adaptations should help elucidate how H. pylori manages persistent infection, and potentially lead to interventions tailored to diverse human populations.

Helicobacter pylori evolution and phenotypic diversification in a changing host

Helicobacter pylori colonizes the stomachs of more than 50% of the world's population, making it one of the most successful of all human pathogens. One striking characteristic of H. pylori biology is its remarkable allelic diversity and genetic variability. Not only does almost every infected person harbour their own individual H. pylori strain, but strains can undergo genetic alteration in vivo, driven by an elevated mutation rate and frequent intraspecific recombination. This genetic variability, which affects both housekeeping and virulence genes, has long been thought to contribute to host adaptation, and several recently published studies support this concept. We review the available knowledge relating to the genetic variation of H. pylori, with special emphasis on the changes that occur during chronic colonization, and argue that H. pylori uses mutation and recombination processes to adapt to its individual host by modifying molecules that interact with the host. Finally, we put forward the hypothesis that the lack of opportunity for intraspecies recombination as a result of the decreasing prevalence of H. pylori could accelerate its disappearance from Western populations.

VacA and HP-NAP, Ying and Yang of Helicobacter pylori-associated gastric inflammation

Helicobacter pylori is a Gram-negative bacterium which infects almost half of the population worldwide and represents the major cause of gastroduodenal pathologies, such as duodenal and gastric ulcer, gastric cancer, B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) and autoimmune gastritis. H. pylori colonization is followed by infiltration of the gastric mucosa by polymorphonuclear cells, macrophages and lymphocytes. Two of the major H. pylori virulence factors are the vacuolating cytotoxin (VacA) and the H. pylori neutrophil-activating protein (HP-NAP). VacA has been proposed as a modulator of immune cell function because of its capacity to interfere with antigen presentation and to inhibit T-cell activation. HP-NAP was designated as neutrophil-activating protein because it stimulates high production of oxygen radicals from neutrophils. We have recently demonstrated that HP-NAP is able to recruit leukocytes in vivo and to stimulate either neutrophils or monocytes to release IL-12, a key cytokine for the differentiation of naive Th cells into the Th1 phenotype. Altogether these evidences indicate that both VacA and HP-NAP play a major role in generating and maintaining the gastric inflammatory response associated with the H. pylori infection.

Helicobacter pylori infection is a potential protective factor against conventional multiple sclerosis in the Japanese population

Persistent Helicobacter pylori (H. pylori) infection is a chronic inflammatory stimulus to hosts with an inverse correlation to atopic disorders. In this study, a total of 105 consecutive multiple sclerosis (MS) patients were divided into 52 opticospinal MS (OSMS) and 53 conventional MS (CMS), and their sera, along with those from 85 healthy controls (HC), were examined by an enzyme-linked immunosorbent assay using antibodies against H. pylori. H. pylori seropositivity was significantly lower in patients with CMS (22.6%) compared with HC (42.4%) and patients with OSMS (51.9%) (p=0.0180 and p=0.0019, respectively). In patients with CMS, H. pylori seropositivity showed a significant inverse association with mean EDSS score and fulfillment of McDonald MRI criteria for space (OR=0.61, p=0.0344 and OR=0.11, p=0.0297). These findings suggest that H. pylori infection is a protective factor against CMS in Japanese.

Inhibition of urease by bismuth(III): Implications for the mechanism of action of bismuth drugs

Bismuth compounds are widely used for the treatment of peptic ulcers and Helicobacter pylori infections. It has been suggested that enzyme inhibition plays an important role in the antibacterial activity of bismuth towards this bacterium. Urease, an enzyme that converts urea into ammonia and carbonic acid, is crucial for colonization of the acidic environment of the stomach by H. pylori. Here, we show that three bismuth complexes exhibit distinct mechanisms of urease inhibition, with some differences dependent on the source of the enzyme. Bi(EDTA) and Bi(Cys)(3) are competitive inhibitors of jack bean urease with K(i) values of 1.74 +/- 0.14 and 1.84 +/- 0.15 mM, while the anti-ulcer drug, ranitidine bismuth citrate (RBC) is a non-competitive inhibitor with a K (i) value of 1.17 +/- 0.09 mM. A (13)C NMR study showed that Bi(Cys)(3) reacts with jack bean urease during a 30 min incubation, releasing free cysteines from the metal complex. Upon incubation with Bi(EDTA) and RBC, the number of accessible cysteine residues in the homohexameric plant enzyme decreased by 5.80 +/- 0.17 and 11.94 +/- 0.13, respectively, after 3 h of reaction with dithiobis(2-nitrobenzoic acid). Kinetic analysis showed that Bi(EDTA) is both a competitive inhibitor and a time-dependent inactivator of the recombinant Klebsiella aerogenes urease. The active C319A mutant of the bacterial enzyme displays a significantly reduced sensitivity toward inactivation by Bi(EDTA) compared with the wild-type enzyme, consistent with binding of Bi(3+) to the active site cysteine (Cys(319)) as the mechanism of enzyme inactivation.

The lipid A 1-phosphatase of Helicobacter pylori is required for resistance to the antimicrobial peptide polymyxin

Modification of the phosphate groups of lipid A with amine-containing substituents, such as phosphoethanolamine, reduces the overall net negative charge of gram-negative bacterial lipopolysaccharide, thereby lowering its affinity to cationic antimicrobial peptides. Modification of the 1 position of Helicobacter pylori lipid A is a two-step process involving the removal of the 1-phosphate group by a lipid A phosphatase, LpxEHP (Hp0021), followed by the addition of a phosphoethanolamine residue catalyzed by EptAHP (Hp0022). To demonstrate the importance of modifying the 1 position of H. pylori lipid A, we generated LpxEHP-deficient mutants in various H. pylori strains by insertion of a chloramphenicol resistance cassette into lpxEHP and examined the significance of LpxE with respect to cationic antimicrobial peptide resistance. Using both mass spectrometry analysis and an in vitro assay system, we showed that the loss of LpxEHP activity in various H. pylori strains resulted in the loss of modification of the 1 position of H. pylori lipid A, thus confirming the function of LpxEHP. Due to its unique lipid A structure, H. pylori is highly resistant to the antimicrobial peptide polymyxin (MIC > 250 microg/ml). However, disruption of lpxEHP in H. pylori results in a dramatic decrease in polymyxin resistance (MIC, 10 microg/ml). In conclusion, we have characterized the first gram-negative LpxE-deficient mutant and have shown the importance of modifying the 1 position of H. pylori lipid A for resistance to polymyxin.

The Helicobacter pylori VacA cytotoxin activates RBL-2H3 cells by inducing cytosolic calcium oscillations

Helicobacter pylori causes an acute inflammatory response followed by chronic infection of the human gastric mucosa. Identification of the bacterial molecules endowed with a pro-inflammatory activity is essential to a molecular understanding of the pathogenesis of H. pylori associated diseases. The vacuolating cytotoxin A (VacA) induces mast cells to release pro-inflammatory cytokines. Here, we show that VacA activates the mast cell line RBL-2H3 by rapidly inducing an oscillation of the level of cytosolic calcium with exocytosis of secretory granules. Cytosolic calcium derives mainly from intracellular stores. VacA also stimulates a calcium-dependent production of pro-inflammatory cytokines, including tumour necrosis factor alpha (TNF-alpha). These observations indicate that VacA may act as a pro-inflammatory factor of H. pylori at very early stages of the innate immune response.

Stable accumulation of sigma54 in Helicobacter pylori requires the novel protein HP0958

Several flagellar genes in Helicobacter pylori are dependent on sigma(54) (RpoN) for their expression. These genes encode components of the basal body, the hook protein, and a minor flagellin, FlaB. A protein-protein interaction map for H. pylori constructed from a high-throughput screen of a yeast two-hybrid assay (http://pim.hybrigenics.com/pimriderext/common/) revealed interactions between sigma(54) and the conserved hypothetical protein HP0958. To see if HP0958 influences sigma(54) function, the corresponding gene was disrupted with a kanamycin resistance gene (aphA3) in H. pylori ATCC 43504 and the resulting mutant was analyzed. The hp0958:aphA3 mutant was nonmotile and failed to produce flagella. Introduction of a functional copy of hp0958 into the genome of the hp0958:aphA3 mutant restored flagellar biogenesis and motility. The hp0958:aphA3 mutant was deficient in expressing two sigma(54)-dependent reporter genes, flaB'-'xylE and hp1120'-'xylE. Levels of sigma(54) in the hp0958 mutant were substantially lower than those in the parental strain, suggesting that the failure of the mutant to express the genes in the RpoN regulon and produce flagella was due to reduced sigma(54) levels. Expressing sigma(54) at high levels by putting rpoN under the control of the ureA promoter restored flagellar biogenesis and motility in the hp0958:aphA3 mutant. Turnover of sigma(54) was more rapid in the hp0958:aphA3 mutant than it was in the wild-type strain, suggesting that HP0958 supports wild-type sigma(54) levels in H. pylori by protecting it from proteolysis.

Occurrence of Helicobacter pylori DNA in the coastal environment of southern Italy (Straits of Messina)

AIMS

The occurrence of Helicobacter pylori in the coastal zone of the Straits of Messina (Italy) as free-living and associated with plankton was studied.

METHODS AND RESULTS

Monthly sampling of seawater and plankton was carried out from April 2002 to March, 2003. All environmental samples analysed by cultural method, did not show the presence of H. pylori. The DNA extracted from all environmental samples was tested by PCR by using primers for H. pylori 16S rRNA, ureA and cagA. 16S rRNA PCR yielded amplified products of 522-bp in 15 of 36 (41.7%) of the environmental samples. By using the ureA primers to amplify the urea signal sequences, the predicted PCR products of 491-bp were obtained from eight (22.2%) of 36 environmental samples. PCR with cagA primers yielded amplified products of 349-bp in DNA extracted of seven of 36 (19.4%) of the environmental samples. When 16S rRNA, ureA and cagA amplified gene sequences were aligned with H. pylori 26695 and J99 genome sequences, we obtained a percentage of alignment over 90%.

CONCLUSIONS

The detection of H. pylori genes in marine samples allows us to consider the marine environment a possible reservoir for this pathogenic bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

The direct detection of H. pylori genes may be relevant in order to consider the marine environment as significant reservoir for this bacterium.

Antagonistic activity against Helicobacter pylori infection in vitro by a strain of Enterococcus faecium TM39

Lactic acid bacteria (LAB) strains from infant feces were screened for anti-Helicobacter pylori use. In the beginning, we selected the strains based on their capability to adhere to the human intestinal epithelial cell (Int-407), colonial enterocyte-like Caco-2 cell, human cervical epithelioid carcinoma cell (HeLa), and human gastric carcinoma cell (TSGH 9201). Then, acid and bile salt tolerance of these LAB strains was evaluated. In addition, the ability of these LAB strains to inhibit the growth of H. pylori and to expel H. pylori cells from TSGH 9201 were studied. The spent culture supernatant (SCS) of a selected strain TM39, i.e., TM39-SCS, significantly inhibited the viability of H. pylori in vitro. It also inhibited the urease activity of H. pylori in vitro. For these antagonistic effects, in addition to pH and lactic acid, some factors in TM39-SCS might play the major role. Treatment of H. pylori with the SCS or cells of strain TM39 significant reduced its binding to TSGH 9201 cells. Although strain TM39 is identified as Enterococcus faecium, it is not vancomycin resistant and is proved to be safe through the invasion study and a 28-day feeding study with Wistar rats.

Toxicity evaluation for an Enterococcus faecium strain TM39 in vitro and in vivo

Previously, we have screened lactic acid bacteria (LAB) strains from infant feces and evaluated their functional properties. We found a strain of Enterococcus faecium termed as TM39 which is acid and bile tolerant, able to adhere to the intestinal epithelium and with antagonistic activity against Helicobacter pylori. In this study, we demonstrate that strain TM39 is not vancomycin resistant, not invasive to human gastric carcinoma cell line TSGH 9201 and human intestinal epithelial cell line Int-407 in vitro. In addition, we have conducted the in vivo study to evaluate the toxicity of this E. faecium strain TM39 in Wistar rats. For such study, cells of strain TM39 were daily oral administrated with dose of 1 x 10(12), 5 x 10(11) and 2 x 10(10) CFU/kg of body weight, respectively, to the rats for 28 consecutive days. There were no adverse effects on the general condition, behavior, growth, feed and water consumption, hematology, clinical chemistry values, organ weights and histopathologic analysis of the rats. Results of this study demonstrate that consumption of strain E. faecium TM39, even in large quantities, is not associated with any obvious signs of toxicity in Wistar rats.

Molecular mechanism of action of major Helicobacter pylori virulence factors

Although Helicobacter pylori infects 50% of the total human population, only a small fraction of the infected people suffer from severe diseases like peptic ulcers and gastric adenocarcinoma. H. pylori strains, host genotypes and environmental factors play important role in deciding the extent and severity of the gastroduodenal diseases. The bacteria has developed a unique set of virulence factors to survive in the extreme ecological niche of human stomach. Together these virulence factors make H. pylori one of the most successful human pathogenic bacteria colonizing more than half of the human population. Understanding the mechanism of action of the major H. pylori virulence factors will shed light into the molecular basis of its pathogenicity.

The multiple cellular activities of the VacA cytotoxin of Helicobacter pylori

Helicobacter pylori has elaborated a unique set of virulence factors that allow it to colonize the stomach wall. These factors include urease, helicoidal shape, flagella, adhesion and pro-inflammatory molecules. Here we discuss the molecular and cellular mechanisms of action of the vacuolating cytotoxin VacA. Its activities are discussed in terms of tissue alterations which promote the release of nutrients necessary to the growth and survival of the bacterium in its nutrient-poor ecological niche. This toxin also shows some pro-inflammatory and immunosuppressive activities which may be functional to the establishment of a chronic type of inflammation.

Membrane channel structure of Helicobacter pylori vacuolating toxin: role of multiple GXXXG motifs in cylindrical channels

Helicobacter pylori is a human pathogen responsible for severe gastric diseases such as peptic ulcers, gastric adenocarcinoma, and gastric lymphoma. Vacuolating toxin (VacA) is crucial in facilitating the colonization of the gastric lining by inducing cell apoptosis and immune suppression. VacA inserts into membranes and forms a hexameric, anion-selective pore. Here we present a structural model of the VacA pore that strongly resembles the structure of an unrelated anion-selective channel, MscS. In our model, Gly residues in GXXXG motifs pack against small Ala or Val side chains to generate the pore. Our model suggests that the same design of two anion-selective channels was achieved by two different evolutionary paths and provides insight into the mechanism of VacA function.

Helicobacter pylori vacuolating cytotoxin enters cells, localizes to the mitochondria, and induces mitochondrial membrane permeability changes correlated to toxin channel activity

The Helicobacter pylori vacuolating cytotoxin (VacA) intoxicates mammalian cells resulting in reduction of mitochondrial transmembrane potential (Delta Psi m reduction) and cytochrome c release, two events consistent with the modulation of mitochondrial membrane permeability. We now demonstrate that the entry of VacA into cells and the capacity of VacA to form anion-selective channels are both essential for Delta Psi m reduction and cytochrome c release. Subsequent to cell entry, a substantial fraction of VacA localizes to the mitochondria. Neither Delta Psi m reduction nor cytochrome c release within VacA-intoxicated cells requires cellular caspase activity. Moreover, VacA cellular activity is not sensitive to cyclosporin A, suggesting that VacA does not induce the mitochondrial permeability transition as a mechanism for Delta Psi m reduction and cytochrome c release. Time-course and dose-response studies indicate that Delta Psi m reduction occurs substantially before and at lower concentrations of VacA than cytochrome c release. Collectively, these results support a model that VacA enters mammalian cells, localizes to the mitochondria, and modulates mitochondrial membrane permeability by a mechanism dependent on toxin channel activity ultimately resulting in cytochrome c release. This model represents a novel mechanism for regulation of a mitochondrial-dependent apoptosis pathway by a bacterial toxin.

Effects ofHelicobacter pylori infection on cell cycle progression and the expression of cell cycle regulatory proteins

Helicobacter pylori lives in the stomach lumen adhering and specifically interacting with gastric epithelial cells. H. pylori infection can cause a broad range of diseases. Although most infected individuals only develop a chronic inflammation of the stomach, some patients progress to chronic gastritis, duodenal ulceration, or, rarely, cancer. H. pylori is able to send and to receive signals from the gastric epithelium, allowing host and bacteria to become linked in a dynamic equilibrium. Several studies have demonstrated that H. pylori infection induces morphological changes of gastric epithelial cells other than cell proliferation, increase of mitosis and mutations. It has also been demonstrated that H. pylori may predispose to cancer by altering gastric epithelial cell turnover acting specifically on transcription factors. Although H. pylori is able to induce several host responses, it specifically perturbs the delicate balance of those factors that usually help to maintain cell homeostasis. The study of mechanisms of interaction between the bacterium and gastric cells will surely help to prevent the increase and diffusion of malignancies all over the world.

Cellular vacuolation and mitochondrial cytochrome c release are independent outcomes of Helicobacter pylori vacuolating cytotoxin activity that are each dependent on membrane channel formation

Helicobacter pylori vacuolating toxin (VacA) is a secreted toxin that is reported to produce multiple effects on mammalian cells. In this study, we explored the relationship between VacA-induced cellular vacuolation and VacA-induced cytochrome c release from mitochondria. Within intoxicated cells, vacuolation precedes cytochrome c release and occurs at lower VacA concentrations, indicating that cellular vacuolation is not a downstream consequence of cytochrome c release. Conversely, bafilomycin A1 blocks VacA-induced vacuolation but not VacA-induced cytochrome c release, which indicates that cytochrome c release is not a downstream consequence of cellular vacuolation. Acid activation of purified VacA is required for entry of VacA into cells, and correspondingly, acid activation of the toxin is required for both vacuolation and cytochrome c release, which suggests that VacA must enter cells to produce these two effects. Single amino acid substitutions (P9A and G14A) that ablate vacuolating activity and membrane channel-forming activity render VacA unable to induce cytochrome c release. Channel blockers known to inhibit cellular vacuolation and VacA membrane channel activity also inhibit cytochrome c release. These data indicate that cellular vacuolation and mitochondrial cytochrome c release are two independent outcomes of VacA intoxication and that both effects are dependent on the formation of anion-selective membrane channels.

Growth phase-dependent response of Helicobacter pylori to iron starvation

Iron is an essential nutrient that is often found in extremely limited available quantities within eukaryotic hosts. Because of this, many pathogenic bacteria have developed regulated networks of genes important for iron uptake and storage. In addition, it has been shown that many bacteria use available iron concentrations as a signal to regulate virulence gene expression. We have utilized DNA microarray technology to identify genes of the human pathogen Helicobacter pylori that are differentially regulated on a growth-inhibiting shift to iron starvation conditions. In addition, the growth phase-dependent expression of these genes was investigated by examining both exponential and stationary growth phase cultures. We identified known iron-regulated genes, as well as a number of genes whose regulation by iron concentration was not previously appreciated. Included in the list of regulated factors were the known virulence genes cagA, vacA, and napA. We examined the effect of iron starvation on the motility of H. pylori and found that exponential- and stationary-phase cultures responded differently to the stress. We further found that while growing cells are rapidly killed by iron starvation, stationary-phase cells show a remarkable ability to survive iron depletion. Finally, bioinformatic analysis of the predicted promoter regions of the differentially regulated genes led to identification of several putative Fur boxes, suggesting a direct role for Fur in iron-dependent regulation of these genes.

Helicobacter pylori tissue tropism: mouse-colonizing strains can target different gastric niches

Studies with the mouse-adapted Helicobacter pylori strain SS1 had supported an idea that infections by this pathogen start in the gastric antrum and spread to the corpus after extensive mucosal damage. This paper shows that the unrelated strain X47 colonizes the corpus preferentially. Differences between strains in preferred gastric region were detected by co-inoculating mice with a mixture of SS1 and X47, and genotyping H. pylori recovered after 2-8 weeks of infection by vacA s allele PCR and RAPD fingerprinting. Mixed infections were found in each of 59 co-inoculated young C57BL/6J mice. On average, however, SS1 was fourfold more abundant than X47 in the antrum and X47 was threefold more abundant than SS1 in the corpus. Similar results were obtained in mice inoculated first with one strain and then the other strain 2 weeks later. SS1 was even more abundant in the antrum of elderly (>1 year old) mice (97 % of isolates). Qualitatively similar SS1 and X47 tissue distributions were seen using unrelated mouse lines (AKR/J, A/J, DBA/2J, BALB/cJ, LG/J, SM/J), but with significantly different SS1 : X47 ratios in some cases. These results suggest the existence of at least two distinct gastric niches whose characteristics may be affected by host genotype and age (physiology), and indicate that strains differ in how effectively they colonize each niche. Differences among gastric regions and the mixed infections that these allow may contribute to H. pylori diversity and genome evolution.

Molecular and cellular mechanisms of action of the vacuolating cytotoxin (VacA) and neutrophil-activating protein (HP-NAP) virulence factors of Helicobacter pylori

Helicobacter pylori has elaborated a unique set of virulence factors that allow it to colonise the stomach wall. These factors include urease, helicoidal shape, flagella and adhesion molecules. Here we discuss the molecular characteristics and mechanisms of action of the vacuolating cytotoxin, VacA, and the neutrophil-activating protein, HP-NAP. Their activities are discussed in terms of tissue alterations, which promote the release of nutrients necessary for the growth and survival of the bacterium in its nutrient-poor ecological niche.

Helicobacter pylori mutants defective in RuvC Holliday junction resolvase display reduced macrophage survival and spontaneous clearance from the murine gastric mucosa

Homologous recombination contributes to the extraordinary genetic diversity of Helicobacter pylori and may be critical for surface antigen expression and adaptation to environmental challenges within the stomach. We generated isogenic, nonpolar H. pylori ruvC mutants to investigate the function of RuvC, a Holliday junction endonuclease that resolves recombinant joints into nicked duplex products. Inactivation of ruvC reduced the frequency of homologous recombination of H. pylori between 17- and 45-fold and increased sensitivity to DNA-damaging agents and the antimicrobial agents levofloxacin and metronidazole. The H. pylori ruvC mutants were more susceptible to oxidative stress and exhibited reduced survival within macrophages. Experiments with the H. pylori SS1 mouse model revealed that the 50% infective dose of the ruvC mutant was approximately 100-fold higher than that of the wild-type SS1 strain. Although the ruvC mutant was able to establish colonization with bacterial loads that were initially similar to those of the parental SS1 strain, infection was spontaneously cleared from the murine gastric mucosa over periods that varied from 36 to 67 days. These results demonstrate that, in this infection model, RuvC is essential for continued survival of H. pylori in vivo and raises the possibility that inactivation of ruvC might be of value in an attenuated vaccine strain.