Search PubMed⌕ Search

Biomedical subjects

M J Blaser

Publications and source records attributed to M J Blaser.

At least 91 records · Page 5Linked to original sources
PubMed1998

An inverse relation between cagA+ strains of Helicobacter pylori infection and risk of esophageal and gastric cardia adenocarcinoma.

Gastric colonization with Helicobacter pylori, especially cagA+ strains, is a risk factor for noncardia gastric adenocarcinoma, but its relationship with gastric cardia adenocarcinoma is unclear. Although incidence rates for noncardia gastric adenocarcinoma have declined steadily, paralleling a decline in H. pylori prevalence, rates for adenocarcinomas of esophagus and gastric cardia have sharply increased in industrialized countries in recent decades. To clarify the role of H. pylori infection in these tumors with divergent incidence trends, we analyzed serum IgG antibodies to H. pylori and to a recombinant fragment of CagA by antigen-specific ELISA among 129 patients newly diagnosed with esophageal/gastric cardia adenocarcinoma, 67 patients with noncardia gastric adenocarcinoma, and 224 population controls. Cancer risks were estimated by odds ratios (OR) and 95% confidence intervals (CI) using logistic regression models. Infection with cagA+ strains was not significantly related to risk for noncardia gastric cancers (OR, 1.4; CI, 0.7-2.8) but was significantly associated with a reduced risk for esophageal/cardia cancers (OR, 0.4; CI, 0.2-0.8). However, there was little association with cagA- strains of H. pylori for either cancer site (OR, 1.0 and 1.1, respectively). These findings suggest that the effects of H. pylori strains on tumor development vary by anatomical site. Further studies are needed to confirm these results and to assess whether the decreasing prevalence of H. pylori, especially cagA+ strains, may be associated with the rising incidence of esophageal/gastric cardia adenocarcinomas in industrialized countries.

Adenocarcinoma↗
PubMed1998

Cure of Helicobacter pylori infection by omeprazole-clarithromycin-based therapy in non-human primates.

Rhesus monkeys raised in colonies tend to become naturally infected by Helicobacter pylori early in life. Earlier attempts to cure H. pylori infection with a 10-day triple therapy (metronidazole, amoxicillin, and peptobismol) were only partially (60%) successful, probably because of preexisting metronidazole resistance. This study was carried out to determine the efficacy of an alternative clarithromycin-omeprazole-based therapy for curing H. pylori infection in Rhesus monkeys (Macaca mulatta), and to examine histologic and serologic correlates of curing. Five monkeys were endoscoped under ketamine anesthesia. Histology and culture of gastric biopsies and serologic tests demonstrated that they were H. pylori-positive. Two animals had not received prior anti-H. pylori treatment, while three other animals had failed triple therapy and carried metronidazole-resistant H. pylori strains. Quadruple therapy with omeprazole, clarithromycin, amoxicillin, and bismuth subsalicylate was given for 10 days to these five animals. All five animals were cured of the infection, and remained H. pylori-free, based on histology and culture at regular intervals for the 5 months posttherapy during which they were followed. Gastritis scores and anti-H. pylori IgG levels decreased in each animal during this period to levels characteristic of uninfected animals. These results indicate that an omeprazole-clarithromycin-based regimen can cure H. pylori infection in Rhesus monkeys, with resolution of abnormal histology and serologic responses. They suggest that this preclinical animal model is useful for testing new anti-H. pylori therapies.

Amoxicillin↗
PubMed1998

The seroprevalence of cagA-positive Helicobacter pylori strains in the spectrum of gastroesophageal reflux disease.

BACKGROUND & AIMS: The role of Helicobacter pylori in the pathogenesis of gastroesophageal reflux disease (GERD) is unknown. We determined the prevalence of cagA-positive (cagA+) H. pylori strains in patients with GERD or its complications compared with controls of similar age. METHODS: A total of 153 consecutive patients with GERD, Barrett's esophagus, and Barrett's esophagus complicated by dysplasia or adenocarcinoma were compared with 57 controls who underwent upper endoscopy for reasons other than GERD. H. pylori infection and CagA antibody status were determined by histology and enzyme-linked immunosorbent assay. RESULTS: H. pylori prevalence was lower (34%) in patients with GERD and its sequelae than in the control group (45.6%)(P = 0.15). Regardless of the group, increasing age was associated with higher prevalence of H. pylori (P = 0.003). When compared with controls (42.3%), the prevalence of cagA+ H. pylori strains decreased (P = 0.008) in patients with more severe complications of GERD (GERD, 36.7% [nonerosive GERD, 41.2%; erosive GERD, 30.8%]; Barrett's esophagus, 13.3%; and Barrett's with adenocarcinoma/dysplasia, 0%). CONCLUSIONS: Prevalence of H. pylori in patients with GERD and its sequelae was lower but not significantly different than that of a control group. However, patients carrying cagA+ strains of H. pylori may be protected against the complications of GERD, especially Barrett's esophagus and its associated dysplasia and adenocarcinoma.

Adult↗
PubMed1998

Acid-induced expression of an LPS-associated gene in Helicobacter pylori.

To investigate urease-independent mechanisms by which Helicobacter pylori resists acid stress, subtractive RNA hybridization was used to identify H. pylori genes whose expression is induced after exposure to acid pH. This approach led to the isolation of a gene that encoded a predicted 34.8kDa protein (WbcJ), which was homologous to known bacterial O-antigen biosynthesis proteins involved in the conversion of GDP-mannose to GDP-fucose. An isogenic wbcJ null mutant strain failed to express O-antigen and Lewis X or Lewis Y determinants and was more sensitive to acid stress than was the wild-type strain. Qualitative differences in LPS profiles were observed in H. pylori cells grown at pH 5 compared with pH 7, which suggests that H. pylori may alter its LPS structure in response to acidic pH. This may be an important adaptation facilitating H. pylori colonization of the acidic gastric environment.

Amino Acid Sequence↗
PubMed1998

Acid-tolerance response in Helicobacter pylori and differences between cagA+ and cagA- strains.

Helicobacter pylori cagA transcription and translation are maximal at pH 6 in stationary phase. The aim of this study was to determine whether H. pylori has an acid-tolerance response and whether that response is related to CagA expression, by investigating whether preexposure to pH 5 or 6 improved survival of cells subsequently exposed to pH 3. Cell number was determined after broth growth, after exposure to pH 5, 6, or 7, and then after a 30-min exposure to pH 3 without urea. H. pylori cells preexposed to pH 6 or 5 survived pH 3 exposure 100-fold better than did cells preexposed to pH 7. Cells of cagA+ strains grown at pH 6 for 48 h, which induced maximal CagA expression, were significantly more susceptible to pH 3 than were wild type cagA- strains or isogenic cagA- knockouts. Thus, H. pylori strains possess a urea-independent acid-tolerance response. Differential acid susceptibility may contribute to preferential colonization of particular H. pylori strains in specific mucus layer niches.

Antigens, Bacterial↗
PubMed1998

Fellowship training in infectious diseases: a report from the regional and national meetings of infectious diseases division chiefs and program directors.

During the 2-year period April 1995 to April 1997, six regional meetings and one national meeting of division chiefs and program directors of adult infectious diseases programs in the United States were held to review fellowship training. Herein, we report data on job availability and job selection for recently graduated fellows. We summarize discussions on decreasing the number of fellows in training, and we outline suggested components of a core clinical curriculum and of three training tracks--clinician track, clinical investigator track, and basic investigator track.

Adult↗
PubMed1998

Review article: Pathogenesis of the transformation from gastritis to malignancy.

Helicobacter pylori acquisition is the main cause of chronic gastritis in humans. In up to half of the infected subjects, chronic gastritis progresses to atrophic gastritis and intestinal metaplasia. During this course, various mechanisms are triggered that may contribute to the pathogenesis of gastric cancer. Such mechanisms include the inflammation-related cascades of cytokine and free radical reactions, up- and downregulation of growth factors and their receptors, and the atrophy-related impairment of acid output and intraluminal acidity. An array of other factors may also have become significant including overgrowth of bacteria other than H. pylori in the hypochlorhydric or achlorhydric stomach, a high dietary consumption of salt, nitrate, or nitrite, smoking, deficiency of vitamins or micronutrients, influence of sex hormones, or an inherited liability of the dividing epithelial cells to gene errors. These factors may vary in effect between populations and individuals but, if active, may affect the cell genome which may further influence the course and progression of chronic gastritis, and can finally result in overt gastric neoplasia. The molecular biology of gastric cancer has revealed a spectrum of gene errors which vary in type and extent between different histological types of cancer, and between individual cases. There now is evidence that the intestinal metaplasia or the gastric epithelium in atrophic gastritis reveal signs of abnormal expression of various regulatory genes well before the appearance of gastric neoplasia. It is possible that the mechanisms leading to mutation of the genes in epithelial cells are triggered very early in the H. pylori gastritis cascade, and that atrophic gastritis and intestinal metaplasia result from these processes.

Animals↗
PubMed1998

DNA sequence conservation and diversity in transposable element IS605 of Helicobacter pylori.

BACKGROUND: IS605, a transposable element-like sequence identified in the virulence-associated cag region of Helicobacter pylori reference strain NCTC11638, is unusual in containing two oppositely-oriented open reading frames whose products are homologues of the single transposases of the unrelated elements, IS200 and IS1341. METHODS: One hundred independent H. pylori isolates from different parts of the world were screened by PCR and dot blot hybridization to determine the presence of IS605. For some positive isolates, southern hybridizations and sequence analyses were done. RESULTS: Of the 100 isolates, 31 were found to contain sequences related to each ORF with orientation and spacing matching those in canonical IS605-hybridizing sequences. No isolate containing just one ORF and not the other was found. The frequencies of IS605 carriage were independent of geographical origin (U.S. vs. non-U.S.), and of the probable virulence of the isolate (cag status, toxin production or vacA alleles, patient symptoms). Southern blot hybridization of six IS605-containing strains revealed one to nine IS605 copies per genome. Two types of DNA sequence diversity were found: first, a specific 100 bp deletion in two isolates; second, base substitution divergence of 0.4% to 7.5% in pairwise comparisons among the eight isolates characterized, a level of divergence similar to that seen in other H. pylori chromosomal genes. CONCLUSIONS: Based on these findings, we speculate that IS605 is a relatively ancient component of the H. pylori gene pool that has proliferated in this species by horizontal gene transfer, homologous recombination, and transposition.

Base Sequence↗
PubMed1998

Differential normalization of mucosal interleukin-8 and interleukin-6 activity after Helicobacter pylori eradication.

There is differential resolution of mucosal infiltration with neutrophils and mononuclear cells following successful Helicobacter pylori eradication. We investigated the effects of H. pylori eradication on mucosal interleukin-8 (IL-8) and IL-6 activity in relation to the resolution of H. pylori-associated gastritis. Eighty-one duodenal ulcer patients with H. pylori infection received dual- or triple-treatment eradication therapy, and mucosal biopsy specimens obtained at the initial and follow-up endoscopic examinations were cultured in vitro for 24 h. The levels of IL-8 and IL-6 were measured by enzyme-linked immunosorbent assays. In the 42 patients in whom H. pylori eradication failed, there was little change in the numbers of neutrophils and mononuclear cells infiltrating the mucosa and in IL-8 and IL-6 activity. In the 39 patients in whom H. pylori was eradicated, there was normalization both in the numbers of infiltrating neutrophils and in mucosal IL-8 activity, which was evident within 1 month following therapy. In contrast, there was a gradual resolution of mononuclear cell infiltration over a 6-month period, accompanied by a gradual normalization in IL-6 levels. Addition of H. pylori to cultures of mucosal tissues induced a significant increase in IL-8 activity in both uninfected control subjects and patients from whom H. pylori was eradicated. However, this introduction yielded a significant increase in IL-6 activity only in the latter group. This study indicates a dichotomy in the changes of mucosal IL-8 and IL-6 activity after H. pylori eradication. The rapid normalization of IL-8 after H. pylori eradication and the ability of H. pylori cells to stimulate IL-8 in control tissues indicate that IL-8 induction is a part of the innate (nonimmune) responses to this organism. In contrast, the results of experiments analyzing IL-6 activity in cultured mucosal tissues suggest that the gradual resolution of mucosal IL-6 activity and mononuclear infiltration after successful eradication observed in vivo may reflect gradually diminishing residual immune responses against H. pylori.

Adult↗
PubMed1998

Experimental infection of Mongolian gerbils with wild-type and mutant Helicobacter pylori strains.

Experimental Helicobacter pylori infection was studied in Mongolian gerbils with fresh human isolates that carry or do not carry cagA (cagA-positive or cagA-negative, respectively), multiply passaged laboratory strains, wild-type strain G1.1, or isogenic ureA, cagA, or vacA mutants of G1.1. Animals were sacrificed 1 to 32 weeks after challenge, the stomach was removed from each animal for quantitative culture, urease test, and histologic testing, and blood was collected for antibody determinations. No colonization occurred after >/=20 in vitro passages of wild-type strain G1.1 or with the ureA mutant of G1.1. In contrast, infection occurred in animals challenged with wild-type G1.1 (99 of 101 animals) or the cagA (25 of 25) or vacA (25 of 29) mutant of G1.1. Infection with G1.1 persisted for at least 8 months. All 15 animals challenged with any of three fresh human cagA-positive isolates became infected, in contrast to only 6 (23%) of 26 animals challenged with one of four fresh human cagA-negative isolates (P < 0.001). Similar to infection in humans, H. pylori colonization of gerbils induced gastric inflammation and a systemic antibody response to H. pylori antigens. These data confirm the utility of gerbils as an animal model of H. pylori infection and indicate the importance of bacterial strain characteristics for successful infection.

Animals↗
PubMed1998

Mutation in the peb1A locus of Campylobacter jejuni reduces interactions with epithelial cells and intestinal colonization of mice.

Campylobacter jejuni is one of the leading causes of bacterial diarrhea throughout the world. We previously found that PEB1 is a homolog of cluster 3 binding proteins of bacterial ABC transporters and that a C. jejuni adhesin, cell-binding factor 1 (CBF1), if not identical to, contains PEB1. A single protein migrating at approximately 27 to 28 kDa was recognized by anti-CBF1 and anti-PEB1. To determine the role that the operon encoding PEB1 plays in C. jejuni adherence, peb1A, the gene encoding PEB1, was disrupted in strain 81-176 by insertion of a kanamycin resistance gene through homologous recombination. Inactivation of this operon completely abolished expression of CBF1, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. In comparison to the wild-type strain, the mutant strain showed 50- to 100-fold less adherence to and 15-fold less invasion of epithelial cells in culture. Mouse challenge studies showed that the rate and duration of intestinal colonization by the mutant were significantly lower and shorter than with the wild-type strain. In summary, PEB1 is identical to a previously identified cell-binding factor, CBF1, in C. jejuni, and the peb1A locus plays an important role in epithelial cell interactions and in intestinal colonization in a mouse model.

Animals↗
PubMed1998

Heterogeneity in levels of vacuolating cytotoxin gene (vacA) transcription among Helicobacter pylori strains.

Broth culture supernatants from Tox+ Helicobacter pylori strains induce vacuolation of HeLa cells in vitro and contain VacA in concentrations that are higher than those found in supernatants from Tox- H. pylori strains. To investigate the basis for this phenomenon, we analyzed the transcription of the vacuolating cytotoxin gene (vacA) in eight Tox+ strains (each with a type s1/m1 vacA genotype) and nine Tox- strains (each with a type s2/m2 vacA genotype). Most of the Tox+ and Tox- strains tested used the same vacA transcriptional start point, but Tox+ strains yielded significantly stronger primer extension signal intensities than did Tox- strains (mean densitometry values of 15.8 +/- 1.9 versus 8.9 +/- 1.7, P = 0. 0016). Correspondingly, when we introduced vacA::xylE transcriptional fusions into the chromosomes of a Tox+ strain (60190) and a Tox- strain (86-313), the level of XylE activity in 60190 vacA::xylE was about 30-fold higher than that in 86-313 vacA::xylE. Sequence analysis and promoter exchange experiments indicated that the different levels of vacA transcription in these two strains cannot be explained solely by a difference in promoter strength. These data indicate that Tox+ and Tox- H. pylori strains typically differ not only in the VacA amino acid sequence but also in the level of vacA transcription.

Artificial Gene Fusion↗
PubMed1998

Evidence for a conjugation-like mechanism of DNA transfer in Helicobacter pylori.

Many strains of Helicobacter pylori are naturally competent for transformation in vitro. Since there is a high degree of genetic variation among H. pylori strains, we sought to determine whether mechanisms of DNA exchange other than transformation exist in these organisms. Studies were done with H. pylori cells that each were resistant to two different antibiotics; the procedure used involved mating of cells on plates or in broth, in the absence or presence of DNase. In each experiment, such matings produced progeny with the markers of both parents. Examination of the full resistance profile and random arbitrarily primed DNA PCR (RAPD-PCR) profiles of the progeny indicated that DNA transfer was bidirectional. DNase treatment reduced but did not eliminate transfer; only the presence of both DNase and a membrane separating the cells did so. For progeny derived from matings in the presence of DNase, antibiotic resistance and RAPD profiles indicated that transfer was unidirectional. DNase-treated cell-free supernatants also did not transform, ruling out transduction. These experiments indicate that both a DNase-sensitive mechanism (transformation) and a DNase-resistant conjugation-like mechanism involving cell-to-cell contact may contribute to DNA transfer between H. pylori cells.

Conjugation, Genetic↗
PubMed1998

Campylobacter fetus surface layer proteins are transported by a type I secretion system.

The virulence of Campylobacter fetus, a bacterial pathogen of ungulates and humans, is mediated in part by the presence of a paracrystalline surface layer (S-layer) that confers serum resistance. The subunits of the S-layer are S-layer proteins (SLPs) that are secreted in the absence of an N-terminal signal sequence and attach to either type A or B C. fetus lipopolysaccharide in a serospecific manner. Antigenic variation of multiple SLPs (encoded by sapA homologs) of type A strain 23D occurs by inversion of a promoter-containing DNA element flanked by two sapA homologs. Cloning and sequencing of the entire 6.2-kb invertible region from C. fetus 23D revealed a probable 5.6-kb operon of four overlapping genes (sapCDEF, with sizes of 1,035, 1,752, 1,284, and 1,302 bp, respectively) transcribed in the opposite direction from sapA. The four genes also were present in the invertible region of type B strain 84-107 and were virtually identical to their counterparts in the type A strain. Although SapC had no database homologies, SapD, SapE, and SapF had predicted amino acid homologies with type I protein secretion systems (typified by Escherichia coli HlyBD/TolC or Erwinia chrysanthemi PrtDEF) that utilize C-terminal secretion signals to mediate the secretion of hemolysins, leukotoxins, or proteases from other bacterial species. Analysis of the C termini of four C. fetus SLPs revealed conserved structures that are potential secretion signals. A C. fetus sapD mutant neither produced nor secreted SLPs. E. coli expressing C. fetus sapA and sapCDEF secreted SapA, indicating that the sapCDEF genes are sufficient for SLP secretion. C. fetus SLPs therefore are transported to the cell surface by a type I secretion system.

Amino Acid Sequence↗
PubMed1998

Differentiation of Campylobacter jejuni serotype O19 strains from non-O19 strains by PCR.

Guillain-Barré syndrome (GBS), a neurologic disease characterized by acute paralysis, is frequently preceded by Campylobacter jejuni infection. Serotype O19 strains are overrepresented among GBS-associated C. jejuni isolates. We previously showed that all O19 strains tested were closely related to one another by randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism analyses. RAPD analysis demonstrated a 1.4-kb band in all O19 strains tested but in no non-O19 strains. We cloned this O19-specific band; nucleotide sequence analysis revealed a truncated open reading frame with significant homology to DNA gyrase subunit B (gyrB) of Helicobacter pylori. PCR using the random primer and a primer specific for gyrB showed that in non-O19 strains, the random primer did not recognize the downstream gyrB binding site. The regions flanking each of the random primer binding sites were amplified by degenerate PCR for further sequencing. Although the random primer had several mismatches with the downstream gyrB binding site, a single nucleotide polymorphism 6 bp upstream from the 3' terminus was found to distinguish O19 and non-O19 strains. PCR using 3'-mismatched primers based on this polymorphism was designed to differentiate O19 strains from non-O19 strains. When a total of 42 (18 O19 and 24 non-O19) strains from five different countries were examined, O19 strains were distinguishable from non-O19 strains in each case. This PCR method should permit identification of O19 C. jejuni strains.

Base Sequence↗
PubMed1998

Expanding allelic diversity of Helicobacter pylori vacA.

The diversity of the gene encoding the vacuolating cytotoxin (vacA) of Helicobacter pylori was analyzed in 98 isolates obtained from different geographic locations. The studies focused on variation in the previously defined s and m regions of vacA, as determined by PCR and direct sequencing. Phylogenetic analysis revealed the existence of four distinct types of s-region alleles: aside from the previously described s1a, s1b, and s2 allelic types, a novel subtype, designated s1c, was found. Subtype s1c was observed exclusively in isolates from East Asia and appears to be the major s1 allele in that part of the world. Three different allelic forms (m1, m2a, and m2b) were detected in the m region. On the basis of sequence alignments, universal PCR primers that allow effective amplification of the s and m regions from H. pylori isolates from all over the world were defined. Amplimers were subsequently analyzed by reverse hybridization onto a line probe assay (LiPA) that allows the simultaneous and highly specific hybridization of the different vacA s- and m-region alleles and tests for the presence of the cytotoxin-associated gene (cagA). This PCR-LiPA method permits rapid analysis of the vacA and cagA status of H. pylori strains for clinical and epidemiological studies and will facilitate identification of any further variations.

Amino Acid Sequence↗