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Biomedical subjects

M J Blaser

Publications and source records attributed to M J Blaser.

At least 127 records · Page 7Linked to original sources
PubMed1997

Epidemiologic and clinical features of Campylobacter jejuni infections.

Gram-negative bacteria of the genus Campylobacter and of related genera frequently colonize the gastrointestinal tracts of humans, other mammals, and birds. One organism, Campylobacter jejuni, has been recognized as an important human pathogen, usually causing a diarrheal illness. Infection is common throughout the world, but clinical and epidemiologic features differ in developed and developing countries. The high incidence of C. jejuni infections and their propensity to invade tissue and to induce inflammation are compatible with a role in the causation of Guillain-Barré syndrome.

Animals↗
PubMed1997

Value of serology as a noninvasive method for evaluating the efficacy of treatment of Helicobacter pylori infection.

The systemic humoral response to Helicobacter pylori was studied in 86 infected adult patients before antimicrobial therapy and at intervals following therapy. Endoscopy with collection of biopsy specimens was performed immediately before treatment; a 13C-labeled urea breath test was performed, and blood specimens were collected before treatment and at 1, 3, 6, 9, and 12 months after treatment. Serum samples from three patient groups (eradication success [n = 50], eradication failure [n = 16], and no treatment [n = 20]) were assayed for IgA and IgG antibodies to H. pylori by enzyme-linked immunosorbent assay. Levels of antibody to H. pylori before treatment were similar in all three groups. As expected, the no treatment and eradication failure groups had no significant changes in antibody levels during the study period. In contrast, for the eradication success group, the specific IgA and IgG antibody levels decreased progressively and significantly. We conclude that serology is a potentially useful way to monitor the success of treatment of H. pylori infection without using invasive or more expensive methods.

Antibodies, Bacterial↗
PubMed1997

Restriction fragment length polymorphism analysis and random amplified polymorphic DNA analysis of Campylobacter jejuni strains isolated from patients with Guillain-Barré syndrome.

Campylobacter jejuni serotype O19 strains associated with the Guillain-Barré syndrome (GBS) and other strains were examined by restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction products of the flaA genes and by random amplified polymorphic DNA (RAPD) analysis. RFLP analysis showed that regardless of LIO serotype, geographic origins, or association with GBS, the O19 isolates shared an identical digestion pattern by each of four restriction endonucleases, DdeI, MboI, MseI, and AluI. In contrast, among C. jejuni O1 or O2 strains, RFLP patterns were different even among strains of the same LIO serotype. The results of the RAPD analysis were consistent with the flaA RFLP data. These data indicate that all of the O19 strains that were tested were closely related to one another whether they were or were not associated with GBS.

Animals↗
PubMed1997

Molecular biology of S-layers.

In this chapter we report on the molecular biology of crystalline surface layers of different bacterial groups. The limited information indicates that there are many variations on a common theme. Sequence variety, antigenic diversity, gene expression, rearrangements, influence of environmental factors and applied aspects are addressed. There is considerable variety in the S-layer composition, which was elucidated by sequence analysis of the corresponding genes. In Corynebacterium glutamicum one major cell wall protein is responsible for the formation of a highly ordered, hexagonal array. In contrast, two abundant surface proteins from the S-layer of Bacillus anthracis. Each protein possesses three S-layer homology motifs and one protein could be a virulence factor. The antigenic diversity and ABC transporters are important features, which have been studied in methanogenic archaea. The expression of the S-layer components is controlled by three genes in the case of Thermus thermophilus. One has repressor activity on the S-layer gene promoter, the second codes for the S-layer protein. The rearrangement by reciprocal recombination was investigated in Campylobacter fetus. 7-8 S-layer proteins with a high degree of homology at the 5' and 3' ends were found. Environmental changes influence the surface properties of Bacillus stearothermophilus. Depending on oxygen supply, this species produces different S-layer proteins. Finally, the molecular bases for some applications are discussed. Recombinant S-layer fusion proteins have been designed for biotechnology.

ATP-Binding Cassette Transporters↗
PubMed1997

T-cell, antibody, and cytokine responses to homologs of the 60-kilodalton heat shock protein in Helicobacter pylori infection.

For Helicobacter pylori, the hsp60 heat shock protein encoded by hspB is being considered as a potential candidate for subunit vaccines. We investigated the humoral and cellular responses to H. pylori hsp60 and its cross-reactivity with the homologous Mycobacterium bovis p65 protein and autologous human hsp60 protein. H. pylori-infected persons had significantly higher levels than uninfected persons of serum immunoglobulin G antibodies recognizing H. pylori hsp60, but not M. bovis p65 or human hsp60, as determined by enzyme-linked immunosorbent assay. In contrast, immunoblotting demonstrated cross-reactivity of H. pylori hsp60 with human hsp60. T-cell recognition of H. pylori hsp60 was found in both infected and uninfected subjects, and there was no recognition of human hsp60. T cells from infected and uninfected subjects that had been activated in response to H. pylori hsp60 or M. bovis p65 were phenotypically similar but appeared to secrete different levels of gamma interferon and interleukin-10. These results demonstrate an apparent difference in the epitopes recognized by the T and B cells responding to H. pylori hsp60 in H. pylori-infected persons. In contrast to the T-cell responses, which were highly variable in all subjects and showed no recognition of autologous proteins, a specific B-cell response that may have cross-reactivity to human hsp60 is evident in some infected subjects.

Adult↗
PubMed1997

Antigenic characterization of Helicobacter pylori strains from different parts of the world.

Although Helicobacter pylori is considered to be relatively homogeneous at the phenotypic level, our aim was to describe its antigenic heterogeneity and to examine differences in host response. Whole-cell lysates of H. pylori strains originally isolated from persons from Africa, the People's Republic of China, Japan, Peru, Thailand, or the United States or from monkeys were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoblots were performed by using sera from H. pylori-infected persons from different areas of the world and rabbit immune sera against H. pylori antigens. Specific H. pylori antibody responses in persons from the United States and the People's Republic of China were analyzed by enzyme-linked immunosorbent assay with antigens prepared from U.S. or Chinese strains. Despite diverse origins, the strains showed conserved major bands of 84, 60, 56, 31, and 25 kDa. Although there were clear differences in minor bands, there was no obvious geographic pattern. The anti-CagA serum recognized 120- to 140-kDa bands in cagA+ strains from around the world. Although antigenic preparations from individual U.S. or Chinese strains were not optimally sensitive for serologic detection of infection in the heterologous country, use of pools of strains largely overcame this phenomenon. We conclude that conserved H. pylori antigens exist and are recognized by sera from persons from many parts of the world. The heterogeneity of H. pylori antigens and the serological responses of infected hosts is not fully explained by geographic differences. Use of pools may allow development of antigens for serologic testing in any country.

Animals↗
PubMed1997

Helicobacter pylori.

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Anti-Bacterial Agents↗
PubMed1997

Characterization of Helicobacter pylori dapE and construction of a conditionally lethal dapE mutant.

Helicobacter pylori colonizes the human gastric mucosa and causes gastritis, ulceration, or gastric cancer. A previously uncharacterized region of the H. pylori genome was identified and sequenced. This region includes a putative operon containing three open reading frames termed gidA (1,866 bp), dapE (1,167 bp), and orf2 (753 bp); the gidA and dapE products are highly homologous to other bacterial proteins. In E. coli, dapE encodes N-succinyl-L-diaminopimelic acid desuccinylase, which catalyzes the hydrolysis of N-succinyl-L-diaminopimelic acid to L-diaminopimelic acid (L-DAP) and succinate. When wild-type H. pylori strains were transformed to select for dapE mutagenesis, mutants were present when plates were supplemented with DAP but not with lysine; orf2 mutants were selected without DAP supplementation. Consistent with the finding that GidA is essential in Escherichia coli, we were unable to obtain a gidA mutant in H. pylori despite evidence that insertional mutagenesis had occurred. The positions of gidA, dapE, and orf2 suggest that they form an operon, which was supported by slot blot RNA hybridization and reverse transcriptase PCR studies. The data imply that the H. pylori dapE mutant may be useful as a conditionally lethal vaccine.

Amidohydrolases↗
PubMed1997

Helicobacter pylori lipopolysaccharide can activate 70Z/3 cells via CD14.

Helicobacter pylori persistently colonizes the human gastrointestinal tract and is associated with chronic gastritis and, in some cases, peptic ulcer disease or gastric neoplasms. One factor in the persistence of this organism may be its inability to elicit a strong inflammatory response. Lipopolysaccharide (LPS) is a proinflammatory substance found in the cell walls of all gram-negative bacteria. H. pylori LPS has been found by several different measures to be less active than LPS from Enterobacteriaceae. This study addresses the role of CD14 and LPS-binding protein in the cellular response to H. pylori LPS. We report that H. pylori LPS activates mammalian cells expressing CD14 at much lower LPS concentrations than those for control cells not expressing CD14. The maximal activation of CD14-70Z/3 cells by H. pylori LPS also requires LPS-binding protein. H. pylori LPS at concentrations as high as 30 microg/ml does not elicit an interleukin-8 (IL-8) response from the epithelial cell line SW620 in the presence of CD14; 10 ng of Escherichia coli LPS per ml elicits a maximal IL-8 response. Furthermore, in contrast to some other types of LPS with little activity, H. pylori LPS does not inhibit the CD14-70Z/3 cell response to E. coli LPS. From these studies, we conclude that H. pylori LPS, though much less active than E. coli LPS, stimulates cells via CD14.

Acute-Phase Proteins↗
PubMed1997

Analysis of F1F0-ATPase from Helicobacter pylori.

The adaptive mechanisms that permit Helicobacter species to survive within the gastric mucosa are not well understood. The proton-translocating F1F0-ATPase is an important enzyme for regulating intracellular pH or synthesizing ATP in many other enteric bacteria; therefore, we used degenerate primers derived from conserved bacterial F1F0-ATPase sequences to PCR amplify and clone the gene (atpD) encoding the H. pylori F1F0-ATPase beta subunit. The deduced amino acid sequences of the F1F0-ATPase beta subunits from H. pylori and Wolinella succinogenes were 85% identical (91% similar). To characterize a potential functional role of F1F0-ATPase in H. pylori, H. pylori or Escherichia coli cells were incubated for 60 min in buffered solutions at pH 7, 6, 5, or 4, with or without 100 microM N,N'-dicyclohexylcarbodiimide (DCCD), a specific inhibitor of F1F0-ATPase. At pH 5 and 4, there was no significant decrease in survival of H. pylori in the presence of DCCD compared to its absence, whereas incubation with DCCD at pH 7 and 6 significantly decreased H. pylori survival. E. coli survival was unaffected by DCCD at any pH value tested. We next disrupted the cloned beta-subunit sequence in E. coli by insertion of a kanamycin resistance cassette and sought to construct an isogenic F1F0-ATPase H. pylori mutant by natural transformation and allelic exchange. In multiple transformations of H. pylori cells grown at pH 6 or 7, no kanamycin-resistant F1F0 mutants were isolated, despite consistently successful mutagenesis of other H. pylori genes by using a similar approach and PCR experiments providing evidence for integration of the kanamycin resistance cassette into atpD. The sensitivity of H. pylori to DCCD at pH 7 and 6, and failure to recover F1F0 H. pylori mutants under similar conditions, suggests that the function of this enzyme is required for survival of H. pylori at these pHs.

Adenosine Triphosphatases↗
PubMed1997

Role of vacuolating cytotoxin in gastritis due to Helicobacter pylori in gnotobiotic piglets.

To investigate the role of the Helicobacter pylori cytotoxin in the pathogenesis of gastritis, gnotobiotic piglets were colonized with either toxigenic H. pylori or a nontoxigenic isogenic mutant. Only piglets given the toxigenic strain developed toxin-neutralizing antibodies (indicating that toxin is expressed in vivo), but there was no difference in bacterial colonization, epithelial vacuolation, or gastritis between the two groups of piglets.

Animals↗
PubMed1997

The Helicobacter pylori genome is modified at CATG by the product of hpyIM.

To understand mechanisms of DNA methylation in Helicobacter pylori, a human pathogen associated with peptic ulcer disease and gastric adenocarcinoma, we cloned a putative DNA methyltransferase gene, hpyIM. This gene contains a 990-bp open reading frame encoding a 329-amino-acid protein, M.HpyI. Sequence analysis revealed that M.HpyI was closely related to CATG-recognizing adenine DNA methyltransferases, including M.NlaIII in N. lactamica. hpyIM was present in all H. pylori strains tested. DNA from wild-type H. pylori strains was resistant to digestion by SphI and NlaIII, which recognize DNA at sites containing CATG, whereas their isogenic hpyIM mutants were susceptible, indicating lack of modification. Overexpression of hpyIM in Escherichia coli rendered DNA from these cells resistant to NlaIII digestion, confirming the role of hpyIM in modifying CATG sites. We conclude that hpyIM encodes a DNA methyltransferase, M.HpyI, that is well conserved among diverse H. pylori strains and that modifies H. pylori genomes at CATG sites.

Amino Acid Sequence↗
PubMed1997

Nested DNA inversion of Campylobacter fetus S-layer genes is recA dependent.

Wild-type strains of Campylobacter fetus are covered by a monomolecular array of surface layer proteins (SLPs) critical for virulence. Each cell possesses eight SLP gene cassettes, tightly clustered in the genome, that encode SLPs of 97 to 149 kDa. Variation of SLP expression occurs by a mechanism of nested DNA rearrangement that involves the inversion of a 6.2-kb sapA promoter-containing element alone or together with one or more flanking SLP gene cassettes. The presence of extensive regions of identity flanking the 5' and 3' ends of each SLP gene cassette and of a Chi-like recognition sequence within the 5' region of identity suggests that rearrangement of SLP gene cassettes may occur by a generalized (RecA-dependent) homologous recombination pathway. To explore this possibility, we cloned C. fetus recA and created mutant strains by marker rescue, in which recA is disrupted in either S+ or S- strains. These mutants then were assessed for their abilities to alter SLP expression either in the presence or absence of a complementary shuttle plasmid harboring native recA. In contrast to all previously reported programmed DNA inversion systems, inversion in C. fetus is recA dependent.

Bacterial Outer Membrane Proteins↗
PubMed1997

Comparison of two enzyme-linked immunosorbent assay tests for diagnosis of Helicobacter pylori infection in China.

An ELISA based on a pool of United States strains of Helicobacter pylori was compared with a newly developed ELISA based on a pool of Chinese strains. Both assays were tested using sera from 132 Chinese study subjects with biopsy-proven H. pylori infection. Using cutpoints designed to yield equal specificities of 94.9% in an uninfected control population, the sensitivity of the Chinese assay was 100.0%, compared to 97.7% for the United States assay (P = 0.25 by McNemar test). These results suggest that a H. pylori assay based on pooled antigens from United States strains will perform as well in the rural Chinese population as one based on antigens from Chinese strains.

Adult↗
PubMed1997

The versatility of Helicobacter pylori in the adaptation to the human stomach.

A growing body of data indicates that H. pylori colonization of human is ancient, which is consistent with its high prevalence, chronicity of carriage, and generally low level of disease, which, when it occurs has only marginal or no effects on host reproductive capacity. All of these phenomena are markers for a relatively benign co-existence, which may include all of the entire spectrum of interactions from parasitism, through commensalism, to symbiosis. Recent studies suggest the emergence of "quasispecies" during prolonged colonization, and the presence of multiple strains colonizing individual hosts. Such observations suggest that concepts of competition between strains and mutualism will be important in understanding the ecology of colonization and its effects on hosts. The presence of particular pathologies in the host may in part be a function of the characteristics of the bacterial population present. At a genomic level, H. pylori appears to adapt to changing conditions by point mutation, genomic rearrangement, and horizontal gene transfer, the latter is favored by its natural competence. The ability of H. pylori to alter phenotypic properties including superficial Lewis antigen expression and secretion of proinflammatory molecules is evidence of its sensitivity to environmental signals from the host. In such a universe, disease outcomes such as ulceration or neoplasia may be considered as accidents secondary to microbial persistence.

Biological Evolution↗