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  • 1
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The plasmids CloDF13-clp03 and CloDF13-clp21, obtained after nitrosoguanidine mutagenesis of pCloDF13 (Andreoli, P.M. and Nijkamp, H.J.J. (1976) Mol. Gen. Genet. 144, 159–170), encode mutant bacteriocin molecules with a reduced ability to penetrate susceptible cells (Gaastra, W., Oudega, B. and De Graaf, F.K. (1978) Biochim. Biophys. Acta 540, 301–312). DNA sequence analysis revealed that both the genes encoding the mutant bacteriocin molecules had a point-mutation which resulted in the replacement of proline54 by serine in the amino-terminal domain of the cloacin, involved in translocation. This alteration had no detectable effect on the predicted secondary structure of the proteins or on the interaction with various monoclonal antibodies. Susceptible cells with a relatively low number of receptor proteins were not killed by the bacteriocins or were less susceptible, but Escherichia coli cells with a relatively high number of efficient and functional receptor proteins were efficiently killed. Immunoblotting experiments with the latter type of cells showed that cloacin-clp03, like native cloacin DF13, was fragmented during uptake by the cells, but at a somewhat slower rate.
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  • 2
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract In Helicobacter pylori, in vitro iron limitation induces the expression of several iron repressible outer membrane proteins (IROMPs), which are not expressed under normal growth conditions. To substantiate their proposed role in virulence of H. pylori, we determined whether these IROMPs are also expressed in vivo. Therefore, we tested whether sera of patients with H. pylori infection contained antibodies against IROMPs. All sera from 20 H. pylori positive patients showed a clear immune response against a 77 kDa heme-binding IROMP in an immunoblot assay. Antibody responses against the other IROMPs were also found, but with lower frequencies. Serum samples from 18 patients negative for H. pylori infection did not show any immunoreactivity with IROMPs. These results indicate that the IROMPs of H. pylori are immunogenic and are expressed in vivo.
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  • 3
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Genetic diversity of 32 Helicobacter pylori strains isolated from patients with gastritis, gastric or duodenal ulcer, carcinoma, or lymphoma was determined by repetitive sequence element polymerase chain reaction (REP-PCR), and by the new typing method restriction fragment end-labelling (RFEL). Furthermore, these two methods were used to investigate a possible correlation between clinical symptoms and the genetic background of Helicobacter pylori. Both REP-PCR and RFEL revealed 31 different patterns for the 32 strains tested, but the pair of isolates with identical REP-PCR patterns was not the same as the pair of isolates with identical RFEL patterns. Computer-assisted analysis of the DNA fingerprints was used to determine similarity coefficients. This analysis revealed no clustering of disease-specific strains by any of the two methods.
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  • 4
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 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.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 59 (1983), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: During incubation of potato tuber discs (Solanum tuberosum L. cv. Bintje) on a callus-inducing medium at 28°C, a high capacity of in vivo alternative pathway respiration develops (75% of uninhibited respiration is azide-resistant). When callus induction takes place at 8°C, only 45% of respiration is resistant to azide. In the lag phase of growth the activity of alternative pathway is low. during the exponential growth phase the activity reaches its maximal rate. This in vivo activity is of the same size at both culture temperatures. As a consequence a greater part of alternative pathway capacity is operating in uninhibited respiration during growth at low temperatures.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 27 (2000), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Genetic recombination in Helicobacter pylori is believed to be involved in host adaptation of this gastric pathogen and uptake of DNA by natural transformation can result in changes in virulence factors as well as antigenic variation. To elucidate the mechanisms involved in natural transformation we tested two genes with homology to known competence genes (dprA and traG) for their role in this process. Insertion mutants in these genes were constructed in two different H. pylori strains and their competence by natural transformation was compared to the wild-type. Mutation of the traG homolog did not reduce competence. Mutation of the dprA gene, however, severely impaired natural transformation both with plasmid and chromosomal DNA. Our data indicate that dprA and comB3 are essential parts of a common pathway for chromosomal and plasmid transformation.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 38 (2003), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: 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.
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  • 8
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Microbial metabolites may influence the metabolic integrity of intestinal epithelial cells and induce mucosal immune responses. Therefore, we investigated the effects of the microbial metabolites butyrate, iso-valerate, and ammonium on Caco-2 cells and macrophages. Barrier functioning was determined by measuring transepithelial electrical resistance and basolateral recoveries of metabolites. The barrier function of Caco-2 cells remained intact after exposures. Basolateral recoveries ranged from 6.2% to 15.2%. Tumour necrosis factor-α and interleukin-10 were measured to determine immune reactions. The Caco-2 cells did not secrete both cytokines. Physiological concentrations of butyrate and iso-valerate stimulated the secretion of tumour necrosis factor-α and suppressed the secretion of interleukin-10 by macrophages that are not protected by an epithelial barrier. In contrast, ammonium concentrations as high as those produced by microbiotas of IBD patients suppressed the release of both cytokines when the barrier function is impaired.
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  • 9
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Reactive oxygen species (ROS) generated by Helicobacter pylori infection have been suggested to be important factors in induction of gastric malignancies. Utilizing electron spin resonance spectrometry, H. pylori-dependent radical formation and hydroxyl- and superoxide-anion radical scavenging activity was investigated. In contrast to previous reports, we found that H. pylori does not produce ROS, but displays superoxide scavenging activity. This scavenging activity was increased in cag-positive H. pylori strains when compared to strains lacking an intact cag pathogenicity island, and was dependent on enzyme activity. We hypothesize that the increased scavenging activity of cag-positive H. pylori strains is an adaptation to the increased inflammatory response associated with the cag-positive genotype of H. pylori.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 28 (2000), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The level of the IgG antibody titer against Helicobacter pylori correlates with the severity of gastritis. H. pylori strains can harbor the so-called pathogenicity island, containing the cytotoxin associated gene (cagA). Since cagA-positive strains are more virulent it can be postulated that the gastritis will be more severe and hence the IgG antibody titer higher. In a cross-sectional study the correlation of IgG antibody titer and cagA status was studied from patients undergoing upper gastrointestinal endoscopy. Biopsy specimens were obtained to determine the H. pylori status. In addition a serum sample was taken for detection of IgG antibodies against H. pylori as well as CagA. A total of 290 patients positive for IgG antibodies against H. pylori were included. Of these 153 were cagA-positive and 137 were cagA-negative. The mean IgG antibody titer was significantly higher in cagA-positive patients compared to cagA-negatives, 0.75 (S.D. 0.22) versus 0.69 (S.D. 0.24) (P=0.033). It is concluded that the IgG antibody titer is significantly higher in patients harboring cagA-positive H. pylori strains. However, in daily practice the level in IgG antibody titer cannot predict whether or not an individual carries a cagA-positive H. pylori strain since major overlap in IgG antibody titer between cagA-positive and cagA-negative patients is present.
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