The Effect of galE Gene Inactivation on Lipopolysaccharide Profile of Helicobacter pylori

The galE gene product, UDP-galactose 4-epimerase, mediates the incorporation of galactose in extracellular polysaccharide materials such as the O-side chain of lipopolysaccharide (LPS). The O-side chain in H. pylori LPS has been shown to cross-react with Lewis x and/or y blood group antigens, suggesting its potential involvement in H. pylori-linked autoimmune disease. To study its role in H. pylori LPS biosynthesis, the galE gene was cloned, sequenced, and a galE-knockout H. pylori strain was constructed. The H. pylori galE gene encoded a protein of 344 amino acids with a molecular weight of 39K. The LPS profile from the galE-knockout H. pylori strain showed a lower molecular weight than that of the parental strain, indicating the involvement of the galE gene in LPS biosynthesis of H. pylori. Received: 15 December 1997 / Accepted: 10 March 1998     

Helicobacter spp. Other Than Helicobacter pylori

Non- H. pylori Helicobacter species (NHPHS) are associated with several important human and animal diseases. In the past year research into this group of bacteria has continued to gain attention, and novel species have been described in new niches owing to improvements in detection methods. Polymerase chain reaction and/or sequencing remain the gold standard for the detection of this genus. New insights into the pathogenesis of the NHPHS in hepatobiliary, gastric, and intestinal diseases were gained. In particular, data revealed interaction between hepatic steatosis and infectious hepatitis in the development of hepatocellular carcinoma. Evidence of an association between hepatitis C virus and Helicobacter spp. in hepatocarcinoma development was also provided; and male sex hormone signaling appeared to influence infectious hepatitis induced by Helicobacter hepaticus . More findings support an association between Helicobacter heilmannii and gastric adenocarcinoma; and in mice, mucins MUC4 and MUC5 but not MUC1 influence the colonization and pathogenesis of Helicobacter felis . Data indicated that the roles of the adaptive immune system in H. hepaticus -induced intestinal tumorigenesis are different in the small and large intestines, and environmental factors, such as bile acids may modulate H. hepaticus carcinogenic potential. New reports in the prevention and eradication of NHPHS showed a protective response against Helicobacter suis induced by vaccine administration, and a successful cross-foster rederivation method successfully eradicated Helicobacter spp. from contaminated mice litters. Overall, the studies provided insights into the pathophysiology of Helicobacter species other than Helicobacter pylori.     

Assessment of the Effectiveness of Low-Pressure UV Light for Inactivation of Helicobacter pylori

Three strains of Helicobacter pylori were exposed to UV light from a low-pressure source to determine log inactivation versus applied fluence. Results indicate that H. pylori is readily inactivated at UV fluences typically used in water treatment regimens. Greater than 4-log₁₀ inactivation was demonstrated on all three strains at fluences of less than 8 mJ cm⁻².     

Biofilm formation by Helicobacter pylori

Helicobacter pylori NCTC 11637 produces a water-insoluble biofilm when grown under defined conditions with a high carbon:nitrogen ratio in continuous culture and in 10% strength Brucella broth supplemented with 3 g l-1 glucose. Biofilm accumulated at the air/liquid interface of the culture. Light microscopy of frozen sections of the biofilm material showed few bacterial cells in the mass of the biofilm. The material stained with periodic acid Schiff's reagent. Fucose, glucose, galactose, and glycero-manno-heptose, N-acetylglucosamine and N-acetylmuramic acid were identified in partially purified and in crude material, using gas chromatography and mass spectrometry. The sugar composition strongly indicates the presence of a polysaccharide as a component of the biofilm material. Antibodies (IgG) to partially purified material were found in both sero-positive and sero-negative individuals. Treatment of the biofilm material with periodic acid reduced or abolished immunoreactivity. Treatment with 5 mol l-1 urea at 100 degrees C and with phenol did not remove antigenic recognition by patient sera. The production of a water-insoluble biofilm by H. pylori may be important in enhancing resistance to host defence factors and antibiotics, and in microenvironmental pH homeostasis facilitating the growth and survival of H. pylori in vivo.     

Phenylphosphonate transport by Helicobacter pylori

BACKGROUND: Helicobacter pylori can utilize phenylphosphonate as a sole source of phosphorus, and it is able to transport the phosphonate N-phosphonoacetyl-L-aspartate. However, H. pylori does not have any genes homologous to those of the known pathways for phosphonate degradation in bacteria, indicating that it must have novel pathways for the transport and metabolism of phosphonates. METHODS: Phenylphosphonate transport by H. pylori was studied in strains LC20, J99 and N6 by the centrifugation through oil method using [(14)C]-labeled phenylphosphonate. RESULTS: The Michaelis constants of transport K(t) and V(max) for phenylphosphonate showed similar kinetics in the three strains. The Arrhenius plot for phenylphosphonate transport rates at permeant concentrations of 50 micromol/L was linear over the temperature range 10-40 degrees C with an activation energy of 3.5 kJ/mol, and a breakpoint between 5 and 10 degrees C. Transport rates increased with monovalent cation size. The effects of various inhibitors were investigated: iodoacetamide, amiloride, valinomycin, and nigericin reduced the rate of phenylphosphonate transport; sodium azide and sodium cyanide increased the transport rate; and monensin had no effect. CONCLUSIONS: The kinetics and properties of H. pylori phenylphosphonate transport were characterized, and the data suggested a carrier-mediated transport mechanism.     

Helicobacter pylori and hormones.

Helicobacter pylori affects gastric acid secretion via several mechanisms. One of these is by changing gastric regulatory physiology. The infection elevates plasma gastrin levels and decreases gastric mucosal expression of the inhibitory peptide somatostatin. These changes may be due to products of H. pylori itself or inflammatory cytokines released in H. pylori infection: acid secretion is inhibited less by a low intra-gastric pH, infusions of cholecystokinin and gastric distention in infected persons. Eradication of H. pylori rapidly decreases basal acid secretion and gastrin-releasing, peptide-stimulated acid secretion. There are now reports that maximally-stimulated acid secretion, a measure of the parietal cell mass, falls significantly six and 12 months after eradication of H. pylori from duodenal ulcer patients. This might be due to withdrawal of the trophic effect of gastrin. However H. pylori can also decrease gastric acid secretion, both through the mechanisms described in Dr. Cave''s paper and by causing gastric mucosal atrophy with loss of parietal cells. The net effect on acid presumably depends on which mechanism predominates. The processes involved may be crucial determinants of clinical outcome. For example, infection with little atrophy and high acid secretion is associated with duodenal ulcers, while infection with atrophy and low acid secretion increases the risk of gastric cancer of the intestinal-type.     

Helicobacter pylori and apoptosis.

In an attempt to understand the diverse effects of infection with Helicobacter pylori on epithelial mucosal mass and consequent clinical outcome, the relationship between H. pylori infection and gastric epithelial cellular turnover has been investigated. Our results indicate that H. pylori increases epithelial cell proliferation and apoptosis in vivo, but that infection with bacteria of the cagA genotype leads to relatively more proliferation than apoptosis. This review explores the causes of the induction of apoptosis in gastric epithelial cells by H. pylori and the consequences of alterations in apoptosis to the maintenance of gastric mucosal homeostasis.     

Immunology of Helicobacter pylori infection.

We have tried to answer several questions in this article, dealing with: ontogenesis of the immune response, presentation of H. pylori antigens to immune cells, systemic vs local immune response, cytokine Th1/Th2 configuration, the role of cytokines, especially represented during H. pylori infection, mimicry phenomena, extragastroduodenal sites and manifestations and finally, vaccine development. The new achievements in the vaccine field, also of Polish groups, were underlined.     

Inhibition of Helicobacter pylori colonization by sulfated gastric mucin.

The role of human gastric mucin in mucosal protection against Helicobacter pylori colonization was investigated. H. pylori cells were incubated with purified intact mucin or its acidic fractions and then examined for their inhibitory capacity of H. pylori attachment to erythrocytes. Titration data established that the inhibitory activity of mucin was associated with its acidic component as the fraction enriched in sialic acid and sulfate showed 16-fold higher inhibitory titer than that of the intact mucin. While the inhibitory titer of acidic mucin fraction was not affected by the removal of sialic acid, the desulfation led to a complete loss of its inhibitory activity, thus pointing towards the importance of sulfate ester groups in this process. The results for the first time point towards the involvement of sulfomucins in the protection of gastric mucosa against colonization by H. pylori.     

Cell-cycle inhibition by Helicobacter pylori L-asparaginase

Helicobacter pylori (H. pylori) is a major human pathogen causing chronic gastritis, peptic ulcer, gastric cancer, and mucosa-associated lymphoid tissue lymphoma. One of the mechanisms whereby it induces damage depends on its interference with proliferation of host tissues. We here describe the discovery of a novel bacterial factor able to inhibit the cell-cycle of exposed cells, both of gastric and non-gastric origin. An integrated approach was adopted to isolate and characterise the molecule from the bacterial culture filtrate produced in a protein-free medium: size-exclusion chromatography, non-reducing gel electrophoresis, mass spectrometry, mutant analysis, recombinant protein expression and enzymatic assays. L-asparaginase was identified as the factor responsible for cell-cycle inhibition of fibroblasts and gastric cell lines. Its effect on cell-cycle was confirmed by inhibitors, a knockout strain and the action of recombinant L-asparaginase on cell lines. Interference with cell-cycle in vitro depended on cell genotype and was related to the expression levels of the concurrent enzyme asparagine synthetase. Bacterial subcellular distribution of L-asparaginase was also analysed along with its immunogenicity. H. pylori L-asparaginase is a novel antigen that functions as a cell-cycle inhibitor of fibroblasts and gastric cell lines. We give evidence supporting a role in the pathogenesis of H. pylori-related diseases and discuss its potential diagnostic application.     

Helicobacter pylori in Barrett's esophagus.

Barrett's esophagus is an anatomicoclinical state in which, due to the prolonged action of gastroesophageal reflux, the squamous epithelium is replaced by columnar epithelium. Helicobacter pylori has been implicated in the pathogenesis of various gastrointestinal disorders and has occasionally been observed in Barrett's esophagus. The aim of this study is to determine the incidence of H. pylori in Barrett's esophagus and try to establish its role in the pathogenesis of this disorder. H. pylori was observed in 31 biopsies (44.3%) of the 70 studied, mainly when the epithelium is of the gastric atrophic-fundic type (p less than 0.01). Its presence shows no relation to the degree of inflammatory activity and does not seem, therefore, to play an important role in the pathogenesis of the lesion.     

Helicobacter pylori associated gastric pathology.

Helicobacter pylori (HP), undoubtedly, the most common world-wide infection plays an important role in pathogenesis of peptic ulcer. Proof for a causal role for HP in peptic ulcer rests in two major points; 1) the majority of ulcer patients are HP infected and the prevalence of this infection for both gastric ulcer (GU) and duodenal ulcer (DU) is much higher than for gender- and age-adjusted controls and 2) the cure of HP infection dramatically reduces ulcer recurrence. Conclusions regarding the mechanisms by which HP induces peptic ulcer are restricted mainly to studies observing the consequences of its eradication by antibiotics combined with gastric inhibitors or bismuth agents. Several specific virulence factors such as cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA) as well as other noxious substances including ammonia, lipopolysaccharide (endotoxin), platelet activating factor (PAF), nitric oxide (NO) and others have been implicated in gastritis and were found to be significantly more frequent in gastric cancer than in gender- and age-matched controls, especially in younger generation. Chronic inflammation, atrophic gastritis, intestinal metaplasia, impaired defense mechanisms combined with hypergastrinemia, deficiency of vitamin C in the stomach , excessive oxygen metabolites and epithelial cell proliferation have been associated with gastric cancer. This multi-step pathway originally proposed by Correa and his colleagues, long before the HP was discovered in the stomach, leads to cancer but may be reversed by eradication of HP. This is, however, a controversial issue because gastric atrophy and intestinal metaplasia may be also caused by other factors such as bile reflux, dietary irritants, and autoimmunity. The implication of HP in MALT-lymphoma is based on the observations that eradication of HP in early stage of low-grade of this tumor leads to complete remission. The significance of HP in non-ulcer dyspepsia remains questionable and requires further studies.     

Helicobacter pylori: therapeutic targets.

Helicobacter pylori is now considered a major pathogen of the upper gastrointestinal tract. It is seen as an important cause of peptic ulceration not associated with NSAID use. It is also increasingly linked to other diseases of the GI tract, although the relationship between the organism and conditions such as gastric cancer, non-ulcer dyspepsia and gastroesophageal reflux disease is not as clear as is the case in peptic ulcer disease. This is probably because of a lack of well-performed, statistically powerful, prospective therapeutic trials that indicate that H. pylori eradication is of benefit in these diseases. The high infection rate without overt disease seen in many populations, especially from developing countries, probably contributes to this "credibility gap." While we have excellent therapeutic regimens available at this time, rational targeting requires that the objective evidence in favor of therapeutic intervention in upper GI disease, as well as the local H. pylori epidemiology, needs to be considered.