Accumulation of polyphosphate granules in Helicobacter pylori cells under anaerobic conditions

Helicobacter pylori is known to transform to coccoid forms which might be involved in faecal-oral transmission. When the bacteria enter the intestine, they encounter anaerobiosis that is unfavourable for growth. The effect of anaerobiosis was investigated to determine whether H. pylori is viable under such conditions. H. pylori in the late logarithmic growth phase transformed from spiral to coccoid forms when transferred to and incubated anaerobically in fresh medium. Acridine orange staining indicated that the viability of coccoid forms was significantly reduced, but still measurable even at day 5 or 7 of anaerobic culture. The cells retained low but significant levels of the major sigma factor RpoD at day 5 or 7 of anaerobic culture. The cellular structures of coccoid forms contained polyphosphate granules at day 1 and even at day 7 when incubated anaerobically, whereas only a few granules were observed under micro-aerobic conditions. Poor formation of polyphosphate granules in micro-aerobic cultures correlated particularly well with lower levels of acridine orange staining. These results suggest that acridine orange-positive anaerobic coccoid forms are viable to a certain extent and that polyphosphate may support this viability.     

Effect of physical environment on survival of Helicobacter pylori.

AIMS: To determine the effects of physical conditions on survival of Helicobacter pylori in aquatic environments. Survival for prolonged time intervals would implicate environmental water as a possible source of infection. METHODS: The effect of ionic strength, pH, urea, protein and composition of incubation atmosphere on the survival of H pylori NCTC 11637 and two clinical isolates (CI 82 and 92) was investigated. RESULTS: H pylori strains survived for longer periods in physiological (0.15M) saline than in 0.05M or 0.6M saline solution. Optimal pH range for survival was between pH 5.8 and 6.9. Addition of urea (final concentration 100 microM/l-1 and 5 mM/l-1) to neutral unbuffered 0.15M saline resulted in a reduction in survival; addition of bovine serum albumin (1%) or gelatin (1%) resulted in variable survival times compared with saline alone. Incubation in a microaerobic gas mixture prolonged survival compared with incubation in air. CONCLUSION: H pylori survival in water over a prolonged period is possible for a range of physical variables. The results indicate that H pylori could survive in environmental water which may thus act as a potential reservoir of infection.     

Quantification of conserved antigens in Helicobacter pylori during different culture conditions.

In this study, we raised monoclonal antibodies (MAbs) against three conserved Helicobacter pylori antigens, i.e., the N-acetylneuraminyllactose-binding fibrillar hemagglutinin, HpaA; the flagellin subunits, FlaA and FlaB; and a species-specific 26-kDa protein. The MAbs were used for the development of sensitive inhibition enzyme-linked immunosorbent assays for quantification of these antigens in H. pylori during various culture conditions. The quantities of these antigens varied considerably (up to 8-fold) during different culture procedures and between strains (up to 10-fold).     

Assessment of Optimal Atmospheric Conditions for Growth of Helicobacter pylori

 The number and diameter of colonies of Helicobacter pylori isolates growing on agar plates were determined to compare five methods that produce a culture atmosphere. No catalyst was applied. No significant difference was found between two hydrogen-based kits that have a different capacity for production of H₂. These hydrogen-based methods were significantly better than all others evaluated, including one kit that produces ascorbic acid that binds with oxygen. Growth was significantly improved when the atmosphere outside the plastic incubation jars was enriched with 10% CO₂, but carbon dioxide enrichment alone (i.e., no reduction of the oxygen concentration) gave a very poor yield. The colony diameter was a sensitive and reliable measure of atmospheric conditions, as the mean intra- and interobserver difference between repeated readings was ≤0.1 mm for 82% and ≤0.2 mm for 95% of the isolates.     

Apoptotic signaling pathway activated by Helicobacter pylori infection and increase of apoptosis-inducing activity under serum-starved conditions

The enhanced gastric epithelial cell apoptosis observed during infection with Helicobacter pylori has been suggested to be of significance in the etiology of gastritis, peptic ulcers, and neoplasia. To investigate the cell death signaling induced by H. pylori infection, human gastric epithelial cells were incubated with H. pylori for up to 72 h. H. pylori infection induced the activation of caspase -8, -9, and -3 and the expression of the proapoptotic Bcl-2 family proteins Bad and Bid. The peak of the activity of the caspases occurred at 24 h. At this time, the inhibition of caspase-8 or -9 almost completely suppressed H. pylori-induced apoptosis. Inhibition of caspase-8 suppressed the expression of Bad and Bid and the subsequent activation of caspase-9 and -3. These observations indicate that H. pylori induces apoptosis through a pathway involving the sequential induction of apical caspase-8 activity, the proapoptotic proteins Bad and Bid, caspase-9 activity, and effector caspase-3 activity. Activation of the pathway was independent of CagA or vacuolating toxin. A membrane fraction of H. pylori was sufficient to activate this pathway, and treatment with proteinase K eliminated the activity. Apoptotic activity of the membrane fraction was significantly increased by incubating the bacteria under serum-starved conditions for 24 h. These observations suggest that environmental conditions in the human stomach could induce H. pylori-mediated pathogenesis, leading to a variety of clinical outcomes.     

Antigenicity of Helicobacter pylori lipopolysaccharides.

An investigation of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of lipopolysaccharides (LPSs) extracted from seven strains of Helicobacter pylori revealed that these molecules were silver stainable and exhibited a high degree of variability in their patterns. Two strains synthesized a variety of sizes of LPS molecules such that fractionation by SDS-PAGE resulted in a stepwise gradation of bands which extended from the top to the bottom of the silver-stained gel. The LPSs from the remaining five strains were made up of molecules which were more homogeneous in size and clustered around two separate areas of the gel. Antigenic analyses of phenol-water-extracted LPSs by immunoblotting and the passive hemagglutination assay suggested that, in addition to strain-specific antigens, all of the LPSs carried a common antigen. Antibodies to this common antigen could be removed from antisera by absorption, and the resulting antisera were used to differentiate strains on the basis of their O antigens by the passive hemagglutination assay technique. The finding that LPSs from 3 of 10 clinical isolates reacted specifically in one or two of the typing antisera suggested that the development of a scheme for differentiating H. pylori on the basis of O antigens is feasible.     

Comparison of isolates of Helicobacter pylori and Helicobacter mustelae.

On the basis of analysis of protein profiles, isolates of Helicobacter pylori and Helicobacter mustelae were less than 40% similar. Cytotoxin produced by H. pylori was not detected in isolates of H. mustelae. Both bacterial species agglutinated human erythrocytes. These results substantiate a taxonomic difference between H. pylori and H. mustelae.     

Lipid A in Helicobacter pylori.

Free lipid A of Helicobacter pylori was characterized with regard to chemical composition, reactivity with anti-lipid A antibodies, and activity in a Limulus lysate assay. The predominant fatty acids of H. pylori lipid A were 3-OH-18:0, 18:0, 3-OH-16:0, 16:0, and 14:0. Hexosamine was present in amounts similar to those in Campylobacter jejuni or Salmonella typhimurium lipid A. The lipopolysaccharide of H. pylori contained 2-keto-3-deoxyoctonic acid, a common constituent of enterobacterial and C. jejuni lipopolysaccharides. In the enzyme-linked immunosorbent assay, the doses of lipid A required to inhibit anti-lipid A by 50% (EI50 values) by absorption of the immune (rabbit) serum were 7.9, 1.2, and 1.4 micrograms of O-deacylated lipid A's from H. pylori, C. jejuni, and S. typhimurium per ml, respectively. The lower reactivity of H. pylori lipid A compared with those of the other two lipid A preparations (as shown by the higher EI50 value) was underscored by the use of a murine monoclonal anti-lipid A antibody in the inhibition assay. An EI50 value was not obtained at the concentrations tested for H. pylori lipid A; the corresponding figures for C. jejuni and S. typhimurium lipid A's were 13 and 14 micrograms/ml, respectively. No inhibition was obtained with H. pylori lipopolysaccharide, which showed a low-molecular-weight profile on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The activity of H. pylori lipid A in the Limulus assay was approximately 71 and 650 times lower than those of C. jejuni and S. typhimurium lipid A's, respectively. These findings suggest that lipid A is an integral part of the outer cell wall of H. pylori. The lower reactivity of H. pylori lipid A with anti-lipid A antibodies and in the Limulus assay compared with that of C. jejuni or S. typhimurium lipid A may be explained by a different composition of the fatty acids, especially the 3-hydroxy fatty acids, and a possible deviating phosphorylation pattern.     

Binding of Helicobacter pylori to sialic acid-containing glycolipids of various origins separated on thin-layer chromatograms.

Two standard strains of Helicobacter pylori, grown on solid or in liquid medium, were studied for their binding to sialic acid-containing glycosphingolipids on thin-layer plates. NCTC 11637, but not strain 11638, bound to mixtures of gangliosides of various human and animal origins with similar binding patterns and also to polyglycosylceramides of human erythrocytes, leukocytes, and placenta. There was an apparent specificity for NeuAc alpha3Gal of the neolacto series of gangliosides, since NeuAc alpha6Gal or ganglio-series gangliosides did not bind.