Kinetics and mechanisms of extracellular protein release by Helicobacter pylori

Disruption of redox homeostasis leads to oxidative DNA damage in spermatocytes of Wolbachia-infected Drosophila simulans

Molecular interactions between symbiotic bacteria and their animal hosts are, as yet, poorly understood. The most widespread bacterial endosymbiont, Wolbachia pipientis, occurs in high density in testes of infected Drosophila simulans and causes cytoplasmic incompatibility (CI), a form of male-derived zygotic lethality. Wolbachia grow and divide within host vacuoles that generate reactive oxygen species (ROS), which in turn stimulate the up-regulation of antioxidant enzymes. These enzymes appear to protect the host from ROS-mediated damage, as there is no obvious fitness cost to Drosophila carrying Wolbachia infections. We have now determined that DNA from Wolbachia-infected mosquito Aedes albopictus (Aa23) cells shows a higher amount of the base 8-oxo-deoxyguanosine, a marker of oxidative DNA damage, than DNA from uninfected cells, and that Wolbachia infection in D. simulans is associated with an increase in DNA strand breaks in meiotic spermatocytes. Feeding exogenous antioxidants to male and female D. simulans dramatically increased Wolbachia numbers with no obvious effects on host fitness. These results suggest that ROS-induced DNA damage in sperm nuclei may contribute to the modification characteristic of CI expression in Wolbachia-infected males and that Wolbachia density is sensitive to redox balance in these flies.

Perspectives on methodology for in vitro culture of Helicobacter pylori

Over the past 25 years, a variety of methods have been developed for culture of Helicobacter pylori in vitro. H. pylori is a capnophilic and microaerophilic organism that is typically cultured using complex culture media. Analysis of H. pylori growth in chemically defined media has provided insight into the nutritional requirements, physiology, and metabolic capacities of this organism.

Perspectives on methodology for in vitro culture of Helicobacter pylori

Over the past 25 years, a variety of methods have been developed for culture of Helicobacter pylori in vitro. H. pylori is a capnophilic and microaerophilic organism that is typically cultured using complex culture media. Analysis of H. pylori growth in chemically defined media has provided insight into the nutritional requirements, physiology, and metabolic capacities of this organism.

The superoxide dismutase SodA is targeted to the periplasm in a SecA-dependent manner by a novel mechanism

The manganese/iron-type superoxide dismutase (SodA) of Rhizobium leguminosarum bv. viciae 3841 is exported to the periplasm of R. l. bv. viciae and Escherichia coli. However, it does not possess a hydrophobic cleaved N-terminal signal peptide typically present in soluble proteins exported by the Sec-dependent (Sec) pathway or the twin-arginine translocation (TAT) pathway. A tatC mutant of R. l. bv. viciae exported SodA to the periplasm, ruling out export of SodA as a complex with a TAT substrate as a chaperone. The export of SodA was unaffected in a secB mutant of E. coli, but its export from R. l. bv. viciae was inhibited by azide, an inhibitor of SecA ATPase activity. A temperature-sensitive secA mutant of E. coli was strongly reduced for SodA export. The 10 N-terminal amino acid residues of SodA were sufficient to target the reporter protein alkaline phosphatase to the periplasm. Our results demonstrate the export of a protein lacking a classical signal peptide to the periplasm by a SecA-dependent, but SecB-independent targeting mechanism. Export of the R. l. bv. viciae SodA to the periplasm was not limited to the genus Rhizobium, but was also observed in other proteobacteria.

Helicobacter pylori acidic stress response factor HP1286 is a YceI homolog with new binding specificity

HP1286 from Helicobacter pylori is among the proteins that play a relevant role in bacterial colonization and persistence in the stomach. Indeed, it was demonstrated to be overexpressed under acidic stress conditions, together with other essential virulence factors. Here we describe its crystal structure, determined at 2.1 A resolution. The molecular model, a dimer characterized by two-fold symmetry, shows that HP1286 structurally belongs to the YceI-like protein family, which in turn is characterized by the lipocalin fold. The latter characterizes proteins possessing an internal cavity with the function of binding and/or transport of amphiphilic molecules. Surprisingly, a molecule of erucamide was found bound in the internal cavity of each monomer of recombinant HP1286, cloned and expressed in an Escherichia coli heterologous system. The shape and length of the cavity indicate that, at variance with other members of the family, HP-YceI has a binding specificity for amphiphilic compounds with a linear chain of about 22 carbon atoms. These features, along with the fact that the protein is secreted by the bacterium and is involved in adaptation to an acidic environment, suggest that its function could be that of sequestering specific fatty acids or amides from the environment, either to supply the bacterium with the fatty acids necessary for its metabolism, or to protect and detoxify it from the detergent-like antimicrobial activity of fatty acids that are eventually present in the external milieu.

Proteomic and functional characterization of the outer membrane vesicles from the gastric pathogen Helicobacter pylori

The gastric pathogen Helicobacter pylori causes a spectrum of gastro‐duodenal diseases, which may be mediated in part by the outer membrane vesicles (OMVs) constitutively shed by the pathogen. We aimed to determine the proteome of H. pylori OMV to help evaluate the mechanisms whereby these structures confer their known immuno‐modulatory and cytotoxic activities to host cells, as such disease‐associated activities are also conferred by the bacterium from which the vesicles are derived. We also evaluated the effect of the OMV on gastric/colonic epithelial cells, duodenal explants and neutrophils. A proteomic analysis of the OMV proteins separated by SDS‐PAGE from two strains of H. pylori (J99 and NCTC 11637) was undertaken and 162 OMV‐associated proteins were identified in J99 and 91 in NCTC 11637 by LC‐MS/MS. The vesicles are rich in membrane proteins, porins, adhesins and several molecules known to modulate chemokine secretion, cell proliferation and other host cellular processes. Further, the OMVs are also vehicles for the carriage of the cytotoxin‐associated gene A cytotoxin in addition to the previously documented toxin, vacuolating cytotoxin. Taken together, it is evident from the proteome of H. pylori OMV that these structures are equipped with the molecules required to interact with host cells in a manner not dissimilar from the intact pathogen.

Gene expression of AGS cells stimulated with released proteins by Helicobacter pylori

BACKGROUND AND AIM

Interactions between released proteins by Helicobacter pylori (H. pylori) and the cells of gastric epithelium to which it adheres may contribute to gastric inflammation and epithelial damage. The present study was performed to evaluate the gene expression of AGS gastric cancer cells stimulated with released proteins by H. pylori.

METHODS

Gene expression of AGS cells to the stimulation by H. pylori-released proteins (G27 strain) were monitored using oligonucleotide microarrays.

RESULTS

Eighty-eight genes (0.88%) and eight genes (0.08%) were up- or downregulated, respectively, by treating AGS cells with H. pylori-released proteins but not by H. pylori adhesion after 12 h of coculture. Out of the selected 40 up- and five downregulated genes, 29 upregulated genes classified as general RNA polymerase II transcription factor activity (GTF2B, PPARGC1A), SH3/SH2 adaptor activity (CRKL), transferase activity (ACLY, CRKL, PIGC, PLK4), and oxidoreductase activity (IDH1) were confirmed to be upregulated by released proteins and not by H. pylori adhesion by real-time reverse transcription-polymerase chain reaction. When the concentrated H. pylori-cultured supernatant prepared by our protocol was treated by boiling, the upregulations of 26 of these 29 genes (89.7%) except for CD160, ZNF268, and PSAT1 disappeared. This confirmed that most of these upregulations were caused by released proteins.

CONCLUSION

Host genes involving transcription, signaling and stress are significantly modulated by the proteins released by H. pylori. This might strengthen the gastroduodenal pathogenesis induced by H. pylori.

Direct analysis of the extracellular proteome from two strains of Helicobacter pylori

Helicobacter pylori extracellular proteins are of interest because of possible roles in pathogenesis, host recognition, and vaccine development. We utilized a unique approach by growing two strains (including one nonsequenced strain) in a defined serum-free medium and directly analyzing the proteins present in the culture supernatants by LC-MS/MS. Over 125 proteins were identified in the extracellular proteomes of two H. pylori strains. Forty-five of these proteins were enriched in the extracellular fraction when compared to soluble cell-associated protein samples. Our analysis confirmed and expanded on the previously reported H. pylori extracellular proteome. Extracellular proteins of interest identified here included cag pathogenicity island protein Cag24 (CagD); proteases HP0657 and HP1012; a polysaccharide deacetylase, HP0310, possibly involved in the hydrolysis of acetyl groups from host N-acetylglucosamine residues or from residues on the cell surface; and HP0953, an uncharacterized protein that appears to be restricted to Helicobacter species that colonize the gastric mucosa. In addition, our analysis found eight previously unidentified outer membrane proteins and two lipoproteins that could be important cell surface proteins.

Human polymorphonuclear leukocytes are sensitive in vitro to Helicobacter pylori vaca toxin

BACKGROUND

Interactions between bacterial components and polymorphonuclear leukocytes (PMNL) play a major pathogenic role in Helicobacter pylori-associated diseases. Activation of PMNL can be induced by contact with whole bacteria or by different H. pylori products released in the extracellular space either by active secretion or by bacterial autolysis. Among these products, H. pylori VacA is a secreted toxin inducing vacuolation and apoptosis of epithelial cells.

METHODS AND RESULTS

We found that non-opsonic human PMNL were sensitive to the vacuolating effect of VacA+ broth culture filtrate (BCF) and of purified VacA toxin. PMNL incubated with VacA+ BCF showed Rab7-positive large intracytoplasmic vacuoles. PMNL preincubation with H. pylori BCF of different phenotypes dramatically potentialized the oxidative burst induced by zymosan, increased phagocytosis of opsonized fluorescent beads, and up-regulated CD11b cell surface expression, but independently of the BCF VacA phenotype. Moreover, by using purified VacA toxin we showed that vacuolation induced in PMNL did not modify the rate of spontaneous PMNL apoptosis measured by caspase 3 activity.

CONCLUSIONS

Taken together, these data showed that human PMNL is a sensitive cell population to H. pylori VacA toxin. However, activation of PMNL (i.e., oxidative burst, phagocytosis, CD11b up-regulation) and PMNL apoptosis are not affected by VacA, raising question about the role of VacA toxin on PMNL in vivo.

Proteomic profiling of cell envelope-associated proteins from Staphylococcus aureus

The emergence of highly virulent community acquired Staphylococcus aureus and continued progression of resistance to multiple antimicrobials, including methicillin and vancomycin, marks the reemergence of S. aureus as a serious health care threat. Investigation of proteins localized to the cell surface could help to elucidate mechanisms of virulence and antibiotic resistance in S. aureus. In this study, proteomic profiling methods were developed to solubilize, display, and evaluate abundance levels of proteins present in the supernatants of the lysostaphin-digested cell envelope from cultured vancomycin-intermediate S. aureus (VISA) cells. Combining approaches of 2-DE or chromatographic separation of proteins with MS analyses resulted in the identification of 144 proteins of particular interest. Of these proteins, 48 contained predicted cell wall localization or export signal motifs, including 14 with distinct covalent peptidoglycan-anchor sites, four of which are uncharacterized to date. One of the two most abundant cell envelope proteins, which showed remarkably high variations in MW and pI in the 2-DE gel display, was the S. aureus surface protein G. The display of numerous secreted proteins that are not covalently cell wall-anchored, suggests that, in the exponential growth phase, secreted proteins can be retained physiologically in the cell envelope and may interact with cell wall-anchored proteins and carbohydrate structures in a manner yet to be determined. The remaining 96 proteins, devoid of recognizable motifs, were repeatedly profiled in the VISA cell envelope fractions. We describe a novel semiquantitative method to determine abundance factors of such proteins in 2-DE gels of cell envelope fractions relative to whole cell lysates and discuss these data in the context of true cell envelope localization versus experimentally caused cell lysis.

Modification of a mammalian cell protein in the presence of [32P-adenylate]NAD: evidence for ADP ribosylation activity associated with Helicobacter pylori

Culture filtrates from Helicobacter pylori promote the transfer of the radiolabel from [32P-adenylate]NAD to one or more heat-labile factors within extracts prepared from several mammalian cell lines, with the predominate radiolabeled species exhibiting an apparent molecular mass of greater than 130 kDa. Our results suggest that several H. pylori strains release a factor that ADP-ribosylates a mammalian target protein.

A novel mechanism of autolysis in Helicobacter pylori: possible involvement of peptidergic substances

BACKGROUND

Helicobacter pylori survival in a hostile acidic environment is known to be caused by its production of urease, which is not released by known secretion pathways. It has been proposed that H. pylori cells undergo spontaneous autolysis during cultivation and that urease becomes surface-associated only concomitant with bacterial autolysis. The aim of this study was to elucidate mechanisms by which H. pylori cells undergo autolysis during cultivation.

MATERIALS AND METHODS

Autolysis of H. pylori KZ109 cells was estimated by measuring the turbidity of the culture, by detection of cytoplasmic protein release into the culture supernatant and by scanning electron microscopic observation of H. pylori cells during cultivation. An autolysis-inducing factor (AIF) was partially purified from the culture supernatant by a partition method using ethyl acetate.

RESULTS

Bacterial turbidity of KZ109 cells was drastically decreased after late-log phase accompanying release of urease and HspB into the extracellular space. Concomitantly, cell lytic activity was detected in the culture supernatant. Scanning electron microscopic observation suggested that partially purified AIF induced cell lysis. It was also shown that the AIF is different from other autolytic enzymes or substances so far reported.

CONCLUSIONS

This study demonstrated the presence of the peptidergic autolytic substances in the culture supernatant of H. pylori KZ109 cells. The results of this study should be useful for further studies aimed at elucidation of the strategy of survival of H. pylori in the gastric environment and elucidation of the mechanisms of pathogenesis induced by H. pylori.

Subproteomes of soluble and structure-bound Helicobacter pylori proteins analyzed by two-dimensional gel electrophoresis and mass spectrometry

Helicobacter pylori is one of the most common bacterial pathogens and causes a variety of diseases, such as peptic ulcer or gastric cancer. Despite intensive study of this human pathogen in the last decades, knowledge about its membrane proteins and, in particular, those which are putative components of the type IV secretion system encoded by the cag pathogenicity island (PAI) remains limited. Our aim is to establish a dynamic two-dimensional electrophoresis-polyacrylamide gel electrophoresis (2-DE-PAGE) database with multiple subproteomes of H. pylori (http://www.mpiib-berlin.mpg.de/2D-PAGE) which facilitates identification of bacterial proteins important in pathogen-host interactions. Using a proteomic approach, we investigated the protein composition of two H. pylori fractions: soluble proteins and structure-bound proteins (including membrane proteins). Both fractions differed markedly in the overall protein composition as determined by 2-DE. The 50 most abundant protein spots in each fraction were identified by peptide mass fingerprinting. We detected four cag PAI proteins, numerous outer membrane proteins (OMPs), the vacuolating cytotoxin VacA, other potential virulence factors, and few ribosomal proteins in the structure-bound fraction. In contrast, catalase (KatA), gamma-glutamyltranspeptidase (Ggt), and the neutrophil-activating protein NapA were found almost exclusively in the soluble protein fraction. The results presented here are an important complement to genome sequence data, and the established 2-D PAGE maps provide a basis for comparative studies of the H. pylori proteome. Such subproteomes in the public domain will be effective instruments for identifying new virulence factors and antigens of potential diagnostic and/or curative value against infections with this important pathogen.

All subtypes of the cytotoxin VacA adsorb to the surface of Helicobacter pylori post-secretion

The major secreted virulence factor of Helicobacter pylori, the vacuolating cytotoxin VacA, is known to insert into eukaryotic membranes and has been observed in association with the surface of H. pylori cells that are actively producing it. Here, it is demonstrated that VacA is capable of interacting with the surface of H. pylori and Escherichia coli after secretion. It is shown that this interaction is resistant to disruption of electrostatic and hydrophobic forces, and that it appears to occur despite truncation of LPS and the removal of trypsin-accessible surface proteins. Adsorption to bacterial cell surfaces was independent of the VacA subtype, suggesting that it is not mediated through recognition of a known receptor by the VacA p58 subunit. Similarly, adsorption to bacterial cell surfaces is unlikely to be instigated by the extreme N-terminus of VacA, since a hydrophilic extension at this location that is known to disrupt VacA-induced vacuolation did not interfere with adsorption to H. pylori cells.

Downregulation of CXCR1 and CXCR2 expression on human neutrophils by Helicobacter pylori: a new pathomechanism in H. pylori infection?

In Helicobacter pylori gastritis, neutrophil activation and migration, which play central roles in the pathogenesis of the disease, are regulated by the neutrophil attractant chemokines interleukin 8 (IL-8) and Groalpha, whose secretion is induced by H. pylori. However, the modulation of the corresponding chemokine receptors CXCR1 and CXCR2 on human neutrophils under the influence of H. pylori has not been investigated. Incubation of neutrophils with cag(+) and cag deletion H. pylori strains resulted in a complete downregulation of the CXCR1 and the CXCR2 receptors after 0.5 h, as tested by fluorescence-activated cell sorter analysis, independent of the cag status. Downregulation of CXCR1 and CXCR2 seems to occur via receptor internalization and rapid degradation, as shown by confocal microscopy and immunoblotting. Neither the proinflammatory cytokines IL-8 and tumor necrosis factor alpha produced by the neutrophils themselves nor H. pylori lipopolysaccharide, which are the known regulators of these two chemokine receptors, was responsible for the downregulation. Reverse transcription-PCR analysis showed that CXCR1 and CXCR2 mRNAs of neutrophils were reduced at a later time than the CXCR1 and CXCR2 proteins. Moreover, cag(+) H. pylori strains induced significantly stronger downregulation of CXCR1 and CXCR2 mRNAs than the cag deletion mutant. Therefore, receptor protein and mRNA downregulation seem to be mediated by two independent mechanisms. Data obtained by immunohistochemistry suggested that downmodulation of CXCR1 and CXCR2 on neutrophils may also occur in vivo in the human stomach during H. pylori infection. Downregulation of CXCR1 and CXCR2 expression on neutrophils in H. pylori infection by H. pylori itself may represent a new mechanism of modulating neutrophil migration and activation in the gastric mucosa.

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.

Molecular fingerprinting of Helicobacter pylori strains from duodenal ulcer patients

AIMS

To characterize the molecular fingerprinting of Helicobacter pylori population isolated in duodenal ulcer patients treated with triple therapy.

METHODS AND RESULTS

Gastric biopsy specimens from corpus and antrum, were cultured for H. pylori isolation. Helicobacter pylori eradication was evaluated after 4 and 16 weeks. DNAs of all isolates were characterized by random amplified polymorphic DNA typing and cagA gene was also detected. After the therapy, five patients harboured the microorganism at 4 weeks and two of them remained H. pylori positive at 16 weeks. The analysis of DNA fingerprinting of strains isolated from antrum and corpus of patients susceptible to treatment, showed similar patterns. Instead, when the therapy was not effective, strains isolated from sequential biopsies from initial and after 4 and 16 weeks, showed distinct fingerprintings and retained the cagA status, over time.

CONCLUSIONS

The drugs used for therapy could exercise an effect in genotypical rearrangement among H. pylori cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The variableness among H. pylori strains represents a way to challenge environmental stress.

Proteins released by Helicobacter pylori in vitro

Secretion of proteins by Helicobacter pylori may contribute to gastric inflammation and epithelial damage. An in vitro analysis was designed to identify proteins released by mechanisms other than nonspecific lysis. The radioactivity of proteins in the supernatant was compared with that of the intact organism by two-dimensional gel phosphorimaging following a 4-h pulse-chase. The ratio of the amount of UreB, a known cytoplasmic protein, in the supernatant to that in the pellet was found to be 0.25, and this was taken as an index of lysis during the experiments (n = 6). Ratios greater than that of UreB were used to distinguish proteins that were selectively released into the medium. Thus, proteins enriched more than 10-fold in the supernatant compared to UreB were identified by mass spectrometry. Sixteen such proteins were present in the supernatant: VacA; a conserved secreted protein (HP1286); putative peptidyl cis-trans isomerase (HP0175); six proteins encoded by HP0305, HP0231, HP0973, HP0721, HP0129, and HP0902; thioredoxin (HP1458); single-stranded-DNA-binding 12RNP2 precursor (HP0827); histone-like DNA-binding protein HU (HP0835); ribosomal protein L11 (HP1202); a putative outer membrane protein (HP1564); and outer membrane proteins Omp21 (HP0913) and Omp20 (HP0912). All except HP0902, thioredoxin, HP0827, HP0835, and HP1202 had a signal peptide. When nalidixic acid, a DNA synthesis inhibitor, was added to inhibit cell division but not protein synthesis, to decrease possible contamination due to outer membrane shedding, two outer membrane proteins (Omp21 and Omp20) disappeared from the supernatant, and the amount of VacA also decreased. Thus, 13 proteins were still enriched greater than 10-fold in the medium after nalidixic acid treatment, suggesting these were released specifically, possibly by secretion. These proteins may be implicated in H. pylori-induced effects on the gastric epithelium.

Proteome analysis of secreted proteins of the gastric pathogen Helicobacter pylori

Secreted proteins (the secretome) of the human pathogen Helicobacter pylori may mediate important pathogen-host interactions, but such proteins are technically difficult to analyze. Here, we report on a comprehensive secretome analysis that uses protein-free culture conditions to minimize autolysis, an efficient recovery method for extracellular proteins, and two-dimensional gel electrophoresis followed by peptide mass fingerprinting for protein resolution and identification. Twenty-six of the 33 separated secreted proteins were identified. Among them were six putative oxidoreductases that may be involved in the modification of protein-disulfide bonds, three flagellar proteins, three defined fragments of the vacuolating toxin VacA, the serine protease HtrA, and eight proteins of unknown function. A cleavage site for the amino-terminal passenger domain of VacA between amino acids 991 and 992 was determined by collision-induced dissociation mass spectrometry. Several of the secreted proteins are interesting targets for antimicrobial chemotherapy and vaccine development.

Cutting edge: urease release by Helicobacter pylori stimulates macrophage inducible nitric oxide synthase

Inducible NO synthase (iNOS) expression and production of NO are both up-regulated with Helicobacter pylori infection in vivo and in vitro. We determined whether major pathogenicity proteins released by H. pylori activate iNOS by coculturing macrophages with wild-type or mutant strains deficient in VacA, CagA, picB product, or urease (ureA(-)). When filters were used to separate H. pylori from macrophages, there was a selective and significant decrease in stimulated iNOS mRNA, protein, and NO(2)(-) production with the ureA(-) strain compared with wild-type and other mutants. Similarly, macrophage NO(2)(-) generation was increased by H. pylori protein water extracts of all strains except ureA(-). Recombinant urease stimulated significant increases in macrophage iNOS expression and NO(2)(-) production. Taken together, these findings indicate a new role for the essential H. pylori survival factor, urease, implicating it in NO-dependent mucosal damage and carcinogenesis.

Clarithromycin increases the release of heat shock protein B from Helicobacter pylori

BACKGROUND

Clarithromycin (CAM) may have certain indirect effects on Helicobacter pylori (H. pylori) other than its inhibitory activity on bacterial growth, as indicated in other infections with Gram-negative micro-organisms. In the present study, we examined the effects of lower concentrations of CAM on the release of heat shock protein B (HspB), one of the major antigenic proteins from H. pylori cells, as well as the changes in humoral immune response and histological degree of antral gastritis in patients who received eradication therapy with CAM.

METHODS

The H. pylori strain 26695 and three CAM-resistant clinical isolates were cultured in broth with and without CAM (2-500 ng/mL). Expression of H. pylori proteins was examined by two-dimensional (2D)-electrophoresis followed by N-terminal amino acid sequencing. Changes in host immune response and histological degree of antral gastritis were monitored in patients with peptic ulcer disease who received H. pylori eradication therapy.

RESULTS

2D electrophoresis showed 26 spots in extracellularly released proteins with different profiles from those in cytoplasmic proteins. The release of HspB increased after incubation with CAM (30-500 ng/mL) in all three H. pylori clinical isolates tested. Patients with failed H. pylori eradication after triple therapy with CAM, but not those with failed eradication after dual therapy without CAM, showed an increase in serum IgG1 and IgG2 antibodies against HspB along with a decrease in the degree of neutrophil and H. pylori colonization density in tissue sections.

CONCLUSIONS

CAM may induce a humoral immune response against H. pylori and a decrease in gastric mucosal inflammation through up-regulation of the release of HspB from the bacteria in infected patients.

Helicobacter pylori growth and urease detection in the chemically defined medium Ham's F-12 nutrient mixture

Obstacles continue to hinder in vitro studies of the gastric human pathogen Helicobacter pylori, including difficulty culturing the organism in the absence of serum or blood, rapid loss of viability following exponential growth due to autolysis, and the necessity for using high starting inocula. We demonstrate that H. pylori grows in the chemically defined broth medium Ham's F-12 nutrient mixture (F-12) in the absence of fetal bovine serum (FBS); this represents a breakthrough for studies in which serum components or proteins interfere with interpretation of results. Cultures can be continually passaged in fresh, FBS-free F-12 medium at an initial inoculum of only approximately 10(3) CFU/ml. All H. pylori strains (n = 21), including fresh clinical isolates, grew in serum-free F-12. H. pylori grew poorly in the related medium, F-10, unless additional zinc was supplied. Enhanced growth of H. pylori in F-12 broth was obtained by addition of bovine serum albumin (BSA) (1 mg/ml), beta-cyclodextrin (200 microg/ml), or cholesterol (50 microg/ml). H. pylori also grew in several simplified versions of F-12 broth lacking glucose and most vitamins but containing hypoxanthine, pyruvate, and all 20 amino acids. On F-12 medium solidified with agar, H. pylori only grew when BSA (98% pure; 1 mg/ml), cholesterol (50 microg/ml), beta-cyclodextrin (200 microg/ml), or FBS (2 to 4%) was added; addition of urea and phenol allowed colorimetric detection of urease activity. Thus, F-12 agar plus cholesterol or beta-cyclodextrin represents the first transparent chemically defined agar and the first urease indicator agar for H. pylori. Several lines of evidence suggested that BSA itself is not responsible for H. pylori growth enhancement in F-12 containing BSA or FBS. Taken together, these innovations represent significant advances in the cultivation and recovery of H. pylori using chemically defined media. Use of F-12 or its derivatives may lead to improved understanding of H. pylori metabolism, virulence factors, and transmission, and result in improved recovery and identification of H. pylori from clinical specimens.

High extracellular levels of Mycobacterium tuberculosis glutamine synthetase and superoxide dismutase in actively growing cultures are due to high expression and extracellular stability rather than to a protein-specific export mechanism

Glutamine synthetase (GS) and superoxide dismutase (SOD), large multimeric enzymes that are thought to play important roles in the pathogenicity of Mycobacterium tuberculosis, are among the bacterium's major culture filtrate proteins in actively growing cultures. Although these proteins lack a leader peptide, their presence in the extracellular medium during early stages of growth suggested that they might be actively secreted. To understand their mechanism of export, we cloned the homologous genes (glnA1 and sodA) from the rapid-growing, nonpathogenic Mycobacterium smegmatis, generated glnA1 and sodA mutants of M. smegmatis by allelic exchange, and quantitated expression and export of both mycobacterial and nonmycobacterial GSs and SODs in these mutants. We also quantitated expression and export of homologous and heterologous SODs from M. tuberculosis. When each of the genes was expressed from a multicopy plasmid, M. smegmatis exported comparable proportions of both the M. tuberculosis and M. smegmatis GSs (in the glnA1 strain) or SODs (in the sodA strain), in contrast to previous observations in wild-type strains. Surprisingly, recombinant M. smegmatis and M. tuberculosis strains even exported nonmycobacterial SODs. To determine the extent to which export of these large, leaderless proteins is expression dependent, we constructed a recombinant M. tuberculosis strain expressing green fluorescent protein (GFP) at high levels and a recombinant M. smegmatis strain coexpressing the M. smegmatis GS, M. smegmatis SOD, and M. tuberculosis BfrB (bacterioferritin) at high levels. The recombinant M. tuberculosis strain exported GFP even in early stages of growth and at proportions very similar to those of the endogenous M. tuberculosis GS and SOD. Similarly, the recombinant M. smegmatis strain exported bacterioferritin, a large (approximately 500-kDa), leaderless, multimeric protein, in proportions comparable to GS and SOD. In contrast, high-level expression of the large, leaderless, multimeric protein malate dehydrogenase did not lead to extracellular accumulation because the protein was highly unstable extracellularly. These findings indicate that, contrary to expectations, export of M. tuberculosis GS and SOD in actively growing cultures is not due to a protein-specific export mechanism, but rather to bacterial leakage or autolysis, and that the extracellular abundance of these enzymes is simply due to their high level of expression and extracellular stability. The same determinants likely explain the presence of other leaderless proteins in the extracellular medium of actively growing M. tuberculosis cultures.

Helicobacter pylori lipopolysaccharide hinders polymorphonuclear leucocyte apoptosis

A prominent histologic feature of Helicobacter pylori infection is a dense infiltration of polymorphonuclear leukocytes (PMNL) in gastric mucosa. H. pylori lipopolysaccharide (LPS) has been recognized as a primary virulence factor evoking acute mucosal inflammatory reaction. Previous works have shown that H. pylori LPS immunologic activities are lower than those of enterobacterial LPS. However, the effect of H. pylori LPS on spontaneous PMNL apoptosis, and mechanisms by which this H. pylori LPS may promote PMNL survival remain to be established. In this study, we investigated, by both morphologic and biochemical approaches, the action of H. pylori LPS on PMNL apoptosis in vitro, using broth culture filtrates (BCF) of H. pylori strains with different genotypes. We found that BCF from H. pylori caused a significant delay in spontaneous PMNL apoptosis and this delay was independent of the VacA, cag pathogenicity island and urease status. We demonstrated that LPS in BCF is responsible for this effect because it was abrogated by the LPS antagonist B287 (a synthetic analog of Rhodobactersphaeroides lipid A). Moreover, BCF from H. pylori induced P42/44MAP kinase activation in PMNL. Similar results were obtained with BCF of an Escherichia coli strain. Taken together these data suggest that longer survival of PMNL induced by H. pylori LPS may increase gastric epithelium injury in H. pylori-associated diseases.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infects over half of the world population. Infection with the bacterium causes gastritis and peptic ulcer disease and is associated with the development of gastric cancers. However, only a small proportion of individuals develop these complications of infection. Therefore, identification of both host and bacterial factors that mediate disease is an intense area of current research interest. This review highlights recent advances in understanding of the mechanisms underlying disease pathophysiology following infection with H. pylori.

Helicobacter pylori colonization and diarrhoeal illness: results of a population-based cross-sectional study in adults

It has been suggested that Helicobacter pylori colonization may protect against diarrhoeagenic gastrointestinal infections. The aim of this analysis was to investigate the association between H. pylori infection and the frequency of diarrhoeal episodes among adults. Helicobacter pylori infection status was determined by 13C-urea breath test. Overall, 784 adults (mean age: 48.7 +/- 17.7; range 18-85 years) who participated in two epidemiological studies were included in the analysis. Overall H. pylori prevalence was 25.5%. Episodes of diarrhoea within prior 3 months were less often reported for H. pylori infected subjects compared with H. pylori negative subjects (40.2 vs. 51.6%, p = 0.016). Compared to H. pylori negative subjects the odds ratio (OR) for the occurrence of diarrhoea within the prior 3 months was 0.63 (95% CI: 0.45-0.87) for H. pylori infected subjects. After adjustment for covariates the OR was 0.67 (95% CI: 0.47-0.95). These results support the hypothesis that colonization with H. pylori may protect from gastrointestinal infections that cause diarrhoea.