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  • 1
    ISSN: 1523-5378
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Background.  Helicobacter pylori factors that contribute to disease outcome are largely unknown, but intimate contact with host cells mediated by outer membrane proteins is thought to play an important role. Expression of the outer membrane proteins OipA, HopZ, SabA, and SabB is regulated by phase-variable dinucleotide repeats in the coding regions of the respective genes. We have evaluated the correlation between the expression status of these four genes and disease outcome of H. pylori infection in a Dutch patient population.Materials and Methods.  H. pylori strains, isolated from 96 Dutch patients with gastritis (n = 29), duodenal ulcer (n = 28), gastric ulcer (n = 21), gastric carcinoma (n = 9), and lymphoma (n = 9), were analyzed for the ‘on/off’ expression status of the H. pylori genes oipA, hopZ, sabA, and sabB by direct DNA sequence analysis of amplified fragments.Results.  The off-status of sabB was significantly associated with duodenal ulcer (p = .036), but not with gastric ulcer. In contrast, the expression status of oipA, hopZ, and sabA did not correlate with disease outcome. Furthermore, lymphoma strains appeared to express a significantly smaller amount of putative adhesins when compared to gastritis, gastric ulcer, duodenal ulcer and gastric carcinoma strains (p 〈 .02 for all groups tested).Conclusion.  The off-status of sabB was found to be associated with duodenal ulcer disease, and thus represents a putative marker for disease outcome. Assuming that SabB is involved in bacterial adhesion, this association suggests that adherent H. pylori are more prone to elimination by the host immune system.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1574-695X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: To study the effect of initial colonisation on Helicobacter pylori gene expression, altered H. pylori gene transcription during co-culture with human gastric epithelial cells was determined. Therefore, an insertion library of H. pylori with random chromosomal fusions to a promoterless cat gene was grown in the presence of HM02 gastric epithelial cells and varying levels of chloramphenicol. One H. pylori transformant was chloramphenicol-resistant in the presence, but chloramphenicol-susceptible in the absence of gastric epithelial HM02 cells. This transformant had the promoterless cat gene inserted into the HP0887 gene, which encodes the vacuolating cytotoxin VacA, an important virulence factor of H. pylori. Reverse transcriptase polymerase chain reaction on cDNA of this transformant confirmed vacA upregulation near HM02 cells. These results show the applicability of this technique to study H. pylori gene regulation in its natural environment.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 38 (2003), S. 0 
    ISSN: 1574-695X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The transcriptional regulation, genetic variation and clinical relevance of the strain-specific hsp12 gene of the human gastric pathogen Helicobacter pylori were investigated. Although the transcription of the hsp12 gene in H. pylori strain 1061 was induced by growth under iron-, pH- and temperature-stress conditions, the gene was not essential for growth under these stress conditions. The locus containing the hsp12 gene showed considerable genetic variation. A total of eight different strain-specific alleles were identified, of which three are mosaic variants of the hsp12 gene and five that are unrelated to the hsp12 gene. The hsp12 locus of six paired sets of strains obtained from patients with 7–10-year time intervals remained unaltered, indicating that genetic variation does not occur during chronic infection. No significant association was found between the presence of a hsp12 gene and peptic ulcer disease in clinical isolates obtained from 26 patients. The stress-regulated, strain-specific hsp12 genes may be involved in adaptation of individual H. pylori strains to their specific hosts, and contribute to long-term colonization of the gastric niche.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 213 (2002), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Urease is an essential virulence factor of the human gastric pathogen Helicobacter pylori, and is expressed to very high levels. The promoter of the urease operon contains sequences resembling the canonical −10 and extended −10 motifs, but no discernible −35 motif. To establish the role of different motifs and regions in the urease promoter, we fused the urease promoter to a genomic lacZ reporter gene in H. pylori, made substitutions in the aforementioned promoter motifs, and also made deletions in the upstream sequences removing regulatory sequences. Substitutions in the −10, extended −10 and predicted −35 motifs all significantly altered expression of the lacZ reporter gene, demonstrating their importance in transcription of the H. pylori urease operon. In contrast, sequential deletions upstream of the −35 region did not affect expression of the lacZ reporter gene. This demonstrates the modular structure of the H. pylori urease promoter, where basal levels of transcription are initiated from a typical σ70 promoter, which requires −10 and extended −10 motifs, and also its −35 motif for efficient transcription. Upstream sequences are not involved in basal levels of urease transcription, but play an important role in responses to environmental stimuli like nickel.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 26 (2002), S. 0 
    ISSN: 1574-6976
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Enteric Campylobacter species cause gastrointestinal diseases in humans. Like almost all organisms, campylobacters have an absolute requirement for iron, but are faced with variable availability of iron in the environment and host tissues. Campylobacters have developed mechanisms to scavenge sufficient iron for metabolism and growth. However, iron also participates in the formation of reactive oxygen species, and this forces pathogens to maintain intracellular iron homeostasis and to cope with oxidative stresses. The presence of two separate, but possibly overlapping iron-responsive regulatory systems, which regulate iron acquisition and oxidative stress defense, and the presence of genes encoding multiple iron acquisition and detoxification systems in Campylobacter indicate the central role that iron plays in Campylobacter gene regulation and virulence.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Helicobacter pylori infection results in chronic gastritis, which is initiated by the release of cytokines like interleukin (IL)-12 and IL-8 from mononuclear cells, and IL-8 from gastric epithelial cells. The severity of gastritis is influenced both by host factors and by bacterial factors such as the Cag proteins and the vacuolating cytotoxin VacA. Amounts of IL-12 and IL-8 produced by monocytic THP-1 cells differed considerably between the eight H. pylori isolates tested, but in contrast to H. pylori-induced IL-8 production by gastric epithelial cells, did not correlate to the Cag and VacA types of the strains. Apparently, in addition to Cag and VacA, other bacterial factors determine the extent in which H. pylori induced IL production in monocytes.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 188 (2000), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: A lacZ-based reporter gene system was used to identify the promoter of the Campylobacter jejuni iron-responsive gene regulator Fur. In other Gram-negative bacteria, the fur promoter is usually located directly upstream of the fur gene and is often autoregulated in response to iron. In this study we demonstrate that expression of the C. jejuni fur gene is controlled from two promoters located in front of the first and second open reading frames upstream of fur. Neither of these promoters was iron-regulated, and the presence of both promoters in front of fur gives higher expression of the lacZ reporter than with either promoter alone. Expression from two distal promoters might be a mechanism for regulating the level of the C. jejuni Fur protein in response to unknown stimuli.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 196 (2001), S. 0 
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: A gene encoding a putative 2[4Fe–4S] ferredoxin (FdxA) was identified upstream of, and divergent to the peroxide stress defense gene ahpC of the microaerophilic pathogen Campylobacter jejuni. The transcription start site of fdxA was located 27 and 28 bp upstream of the fdxA start codon. Transcriptional fusions of the fdxA promoter to a lacZ reporter gene demonstrated that expression of fdxA is iron-induced, and thus oppositely regulated to the iron-repressed ahpC gene. Insertional mutagenesis of the fdxA gene did not affect microaerobic growth of C. jejuni, but significantly reduced aerotolerance of C. jejuni. The fdxA gene is the first reported iron-induced gene of C. jejuni, and encodes a novel component of its oxidative stress defense.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The Escherichia coli-based Fur titration assay (FURTA), although a powerful tool for identification of genes regulated by the ferric uptake regulator (Fur), was unsuccessful for the gastric pathogen Helicobacter pylori. The FURTA was modified by construction of an E. coli indicator strain producing H. pylori Fur only. The promoter regions of the ferric citrate receptor homolog fecA2 and the riboflavin synthesis gene ribBA were both positive in the modified FURTA, but negative in the original FURTA. Transcription of fecA2 and ribBA was demonstrated to be iron-repressed in H. pylori. This type of modification should allow FURTA analysis for bacteria with Fur binding sequences poorly recognized by E. coli Fur.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 44 (2005), S. 0 
    ISSN: 1574-695X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: To facilitate gene expression analysis in the human gastric pathogen Helicobacter pylori, we constructed the plasmids pHPLAC-KAN and pHPLAC-CAT containing a promoterless Escherichia coli lacZ gene located upstream from the antibiotic resistance genes aphA-3 or cat, respectively. The suitability of the plasmids for H. pylori mutagenesis and gene expression analysis was evaluated by plasmid integration into the genome of H. pylori strain 1061 by single homologous recombination, using the rpl9 gene encoding ribosomal protein L9 as target. By monitoring β-galactosidase production from the resulting rpl9::lacZ fusion, it was demonstrated that H. pylori rpl9 displays the classical growth phase-dependent regulation of components of the protein synthesis machinery, as β-galactosidase production dropped fivefold in the stationary growth phase. The plasmids described in this study extend our methodological repertoire for genetic modification and molecular analysis of H. pylori, and may also be of use for other bacteria, as the resistance cassettes and the lacZ gene are active in the related Campylobacter species.
    Materialart: Digitale Medien
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