Potential involvement of several nitroreductases in metronidazole resistance in Helicobacter pylori

Susceptibility of Helicobacter pylori to the antibiotic metronidazole has been attributed to the activity of an oxygen-insensitive NADPH-dependent nitroreductase (RdxA), with resistance to this antimicrobial arising from null mutations in rdxA. To obtain a better understanding of the factors involved in resistance, nitroreductase and metronidazole reduction activities were investigated in matched pairs of clinical and laboratory-derived sensitive and resistant H. pylori strains. Significant differences in enzyme activities were observed between sensitive and resistant strains, suggesting that metronidazole susceptibility in H. pylori was associated with more than one enzyme activity. To establish the mutations occurring in rdxA, the genes from seventeen bacterial strains, including matched pairs were sequenced. To assess whether metronidazole was responsible for inducing random mutations in this gene, the complete nucleotide sequence of gene hp0630, encoding an NAD(P)H-quinone reductase which also has NADPH-dependent nitroreductase activity, was determined in the same strains. All resistant strains showed nonsense, missense, or frameshift mutations randomly throughout rdxA. In contrast, no mutations were observed in hp0630. The results confirmed the presence of rdxA null mutations in resistant strains and suggested that other factors involved in the metabolism of metronidazole contributed to the resistant phenotype.

Association between the IgG subclass response, inflammation and disease status in Helicobacter pylori infection

BACKGROUND

In many viral, bacterial and parasitic infections the Immunoglobulin G (IgG) subclass response has been shown to correlate with severity of inflammation and disease outcome. The aim of the present study was to investigate the association between the IgG subclass response to Helicobacter pylori infection and disease and inflammation.

METHODS

Eighty-three symptomatic patients undergoing endoscopic examination were included in the study. Upon endoscopic examination, the presence of ulceration was noted and biopsy specimens were collected from the gastric antrum, body and transitional zone. Blood was also collected from each patient. Gastric biopsy sections were graded using the Sydney system. H. pylori specific IgG, IgG1, IgG2, IgG3 and IgG4 were measured by ELISA. The IgG subclass was also examined retrospectively in sera collected from 20 patients previously proven to have duodenal ulcer (DU).

RESULTS

The results of histological examination and IgG serology showed 35 subjects to be H. pylori negative and 48 to be H. pylori positive. Of the 48 H. pylori positive subjects, 25 were diagnosed with functional dyspepsia (FD), 14 with current DU and 9 with evidence of past DU. Significantly higher levels of IgG2 antibodies were found in patients with DU as compared with patients with FD (P < 0.01). In addition, significantly higher IgG3 subclass antibody levels were associated with chronic inflammatory cells in the body (P < 0.05) and active inflammatory cells in the transitional zone (P < 0.01). A significantly increased level of IgG1 antibodies was associated with lower levels of colonization in the gastric antrum.

CONCLUSION

The results of this study suggest that the IgG subclass response in subjects infected with H. pylori may be a marker of DU disease as well as increased levels of inflammation.

Oxidases and reductases are involved in metronidazole sensitivity in Helicobacter pylori

Helicobacter pylori is a contributing factor to the development of gastric and duodenal ulcers and some gastric cancers. Some therapeutic regimes comprise of a number of components, one of which is the antimicrobial metronidazole. A problem with these therapies is the increasing prevalence of metronidazole-resistant (MtrR) H. pylori strains. Several resistance mechanisms have been proposed, and this study addresses the 'scavenging of oxygen' hypothesis. Spectrophotometric assays of cytosolic fractions indicated that metronidazole-sensitive (MtrS) H. pylori isolates had 2.6-fold greater nicotinamide adenine dinucleotide (NADH) oxidase activity, 34-fold greater NADH nitroreductase activity, and eightfold greater nicotinamide adenine dinucleotide phosphate (NADPH) nitroreductase activity than cytosolic fractions from matched MtrR strains. Electrophoresis of cytosolic fractions in non-denaturing gels showed up to 10 protein bands when stained with Coomassie blue. Activity staining of non-denaturing, non-reducing polyacrylamide gels detected NAD(P)H oxidase, disulphide reductase, tetrazolium reductase and nitroreductase activities in the protein bands. Oxidase and reductase activities observed in a band from MtrS strains were absent in the corresponding band from MtrR strains. This band comprised at least 13 proteins, and the major constituent was identified as an alkyl hydroperoxide reductase AhpC subunit. The absence of oxidase and reductase activities in the band from MtrR strains indicated a correlation between the activity of the proteins in this band and the metronidazole-sensitive phenotype.

The Helicobacter pylori pyrB gene encoding aspartate carbamoyltransferase is essential for bacterial survival

The production of defined isogenic Helicobacter pylori pyrB mutants was undertaken to investigate the role of aspartate carbamoyltransferase (encoded by pyrB) in the survival of the bacterium. The complete structural gene for aspartate carbamoyltransferase from H. pylori strain RU1 was cloned into Escherichia coli by complementation of a pyrB auxotrophic mutant to facilitate the construction of a pyrB-disrupted copy in E. coli. The H. pylori pyrB gene had high similarity to other bacterial pyrB genes, and the phylogenetic clustering with different species was consistent with functional characteristics of the ACTase. The transcription initiation site for H. pylori pyrB-mRNA was mapped 25 bp upstream of the ATG start codon, and potential promoter regions were identified. In order to construct an isogenic pyrB H. pylori mutant by natural transformation and allelic exchange, the plasmid insert containing pyrB was disrupted by insertional mutagenesis of a chloramphenicol transferase gene cassette. In multiple transformations of H. pylori cells, no chloramphenicol-resistant pyrB mutants were isolated. Successful mutagenesis of other H. pylori genes and PCR amplification of the recombined gene demonstrated that the ACTase-negative mutants had been constructed by allelic exchange involving simultaneous replacement of the pyrB gene with the chloramphenicol-pyrB-disrupted copy. These findings suggested that the ACTase enzyme is essential for the survival of H. pylori.

Use of digoxigenin-labelled ampicillin in the identification of penicillin-binding proteins in Helicobacter pylori

Amoxycillin is used in current therapeutic regimens to treat the infection caused by the human gastric pathogen, Helicobacter pylori. The penicillin-binding proteins (PBPs) are the primary targets for the beta-lactam antibiotics, such as amoxycillin, and are involved in the terminal stages of peptidoglycan synthesis. They also play active roles in the determination and maintenance of cellular morphology. It was believed that an organism with a complex morphology, such as H. pylori, would have more than the three PBPs previously suggested. Using digoxigenin-labelled ampicillin (DIG-ampicillin), we report the identification of eight PBPs in H. pylori with masses of 72, 62, 54, 50, 44, 33.5, 30.5 and 28 kDa. A smaller (21 kDa) ninth band was also detected, which may represent another PBP. However, the relatively small size of this apparent PBP raises questions as to whether this is a true PBP. In an attempt to identify the PBPs to which amoxycillin preferentially binds, amoxycillin was used in competition assays with DIG-ampicillin. It appeared that amoxycillin inhibited the binding of DIG-ampicillin to only the 72 kDa PBP. The experimental data were also compared with the seven putative PBPs identified in the two published H. pylori genomes, most of which correlate with the experimental data. To investigate further the properties of these PBPs, the seven putative PBP genes identified in the H. pylori genomes were examined. The derived amino acid sequences of the putative PBPs were examined for the three characteristic motifs found in all conventional PBPs, SXXK, SXN and KTG. We were able to determine that all of the putative PBPs had at least one of these motifs, but none possessed all three motifs with the characteristics of conventional PBPs. These findings suggest that the PBPs of H. pylori are unique.

Fumarate metabolism and the microaerophily of Campylobacter species

(1) The role of fumarate metabolism in the microaerophily of the Campylobacter genus and the effects of therapeutic agents against it were investigated. (2) NMR spectroscopy was employed to determine the properties of Campylobacter fumarase (Fum) and fumarate reductase (Frd). Radiotracer analysis was used to determine the production of carbon dioxide by Campylobacter cells. Standard microbiological techniques were used to measure the effects of environmental conditions and inhibitors on bacterial growth. (3) All Campylobacter species tested showed both Fum and Frd activities. Frd activity was observed with or without the addition of an exogenous electron donor in the particulate fractions obtained from lysates. Fumarate was oxidized to carbon dioxide via the acetyl-CoA cleavage pathway. The genes encoding proteins involved in fumarate metabolism were identified in the Campylobacter jejuni genome. Cells grew better in atmospheres with 5 and 10% oxygen levels. Fum activity was the same in cultures grown under different oxygen tensions and did not vary with the age of cultures. Frd activity was higher in cultures which grew at faster rates and decreased with the age of cultures. Four Frd inhibitors showed bactericidal effects against Campylobacter spp. with different potencies. The relative strengths of inhibition of the compounds followed the same order as the bactericidal effects. (4) The results suggested that Frd and Fum are constitutive and play a fundamental role in these microaerophiles which show characteristics of anaerobic metabolism, and that the Frd inhibitors tested would not be of therapeutic use.

Metabolism and genetics of Helicobacter pylori: the genome era

The publication of the complete sequence of Helicobacter pylori 26695 in 1997 and more recently that of strain J99 has provided new insight into the biology of this organism. In this review, we attempt to analyze and interpret the information provided by sequence annotations and to compare these data with those provided by experimental analyses. After a brief description of the general features of the genomes of the two sequenced strains, the principal metabolic pathways are analyzed. In particular, the enzymes encoded by H. pylori involved in fermentative and oxidative metabolism, lipopolysaccharide biosynthesis, nucleotide biosynthesis, aerobic and anaerobic respiration, and iron and nitrogen assimilation are described, and the areas of controversy between the experimental data and those provided by the sequence annotation are discussed. The role of urease, particularly in pH homeostasis, and other specialized mechanisms developed by the bacterium to maintain its internal pH are also considered. The replicational, transcriptional, and translational apparatuses are reviewed, as is the regulatory network. The numerous findings on the metabolism of the bacteria and the paucity of gene expression regulation systems are indicative of the high level of adaptation to the human gastric environment. Arguments in favor of the diversity of H. pylori and molecular data reflecting possible mechanisms involved in this diversity are presented. Finally, we compare the numerous experimental data on the colonization factors and those provided from the genome sequence annotation, in particular for genes involved in motility and adherence of the bacterium to the gastric tissue.

The tricarboxylic acid cycle of Helicobacter pylori

The composition and properties of the tricarboxylic acid cycle of the microaerophilic human pathogen Helicobacter pylori were investigated in situ and in cell extracts using [1H]- and [13C]-NMR spectroscopy and spectrophotometry. NMR spectroscopy assays enabled highly specific measurements of some enzyme activities, previously not possible using spectrophotometry, in in situ studies with H. pylori, thus providing the first accurate picture of the complete tricarboxylic acid cycle of the bacterium. The presence, cellular location and kinetic parameters of citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate oxidase, fumarate reductase, fumarase, malate dehydrogenase, and malate synthase activities in H. pylori are described. The absence of other enzyme activities of the cycle, including alpha-ketoglutarate dehydrogenase, succinyl-CoA synthetase, and succinate dehydrogenase also are shown. The H. pylori tricarboxylic acid cycle appears to be a noncyclic, branched pathway, characteristic of anaerobic metabolism, directed towards the production of succinate in the reductive dicarboxylic acid branch and alpha-ketoglutarate in the oxidative tricarboxylic acid branch. Both branches were metabolically linked by the presence of alpha-ketoglutarate oxidase activity. Under the growth conditions employed, H. pylori did not possess an operational glyoxylate bypass, owing to the absence of isocitrate lyase activity; nor a gamma-aminobutyrate shunt, owing to the absence of both gamma-aminobutyrate transaminase and succinic semialdehyde dehydrogenase activities. The catalytic and regulatory properties of the H. pylori tricarboxylic acid cycle enzymes are discussed by comparing their amino acid sequences with those of other, more extensively studied enzymes.

The prevalence of antibody to CagA in children is not a marker for specific disease

BACKGROUND

In adults, a high prevalence of antibody to the cytotoxin-associated antigen (CagA) of Helicobacter pylori has been linked to the development of more serious gastroduodenal disease. Few investigators have examined this association in children. The purpose of this study was to investigate the seroprevalence of antibody to the CagA antigen as well as other specific H. pylori antigens in children.

METHODS

By use of an immunoblot analysis kit, the immune response to specific H. pylori antigens in serum collected from 21 H. pylori-positive symptomatic Australian children, 5 with peptic ulcer disease and 16 with nonulcer dyspepsia, and 33 H. pylori-positive asymptomatic Chinese children. Sera from 20 H. pylori-negative symptomatic Australian children were used as control subjects.

RESULTS

Antibody responses to the 26.5-kDa, 30-kDa, and 116-kDa (CagA) antigens were found to be the most prevalent, with 81.5%, 79.6%, and 76% of children, respectively, mounting a response. In contrast, antibody responses to the 19.5-kDa, 35-kDa, 45-kDa, 60-kDa, 89 kDa (VacA), and 180-kDa antigens occurred in 55.5%, 24%, 16.7%, 63%, 37%, and 7.4% of children, respectively. A higher prevalence of antibody response to CagA was found in the symptomatic Australian children with peptic ulcer disease (100%) compared with prevalence in those with nonulcer dyspepsia (56.3%), but the difference did not reach statistical significance. No significant difference was found between the prevalence of antibody to CagA in the Australian peptic ulcer disease group (100%) and that in the asymptomatic Chinese children (81.8%).

CONCLUSION

These results suggest that in children CagA is not a marker of specific disease development.

A novel mechanism for resistance to the antimetabolite N-phosphonoacetyl-L-aspartate by Helicobacter pylori

The mechanism of resistance to N-phosphonoacetyl-L-aspartate (PALA), a potent inhibitor of aspartate carbamoyltransferase (which catalyzes the first committed step of de novo pyrimidine biosynthesis), in Helicobacter pylori was investigated. At a 1 mM concentration, PALA had no effects on the growth and viability of H. pylori. The inhibitor was taken up by H. pylori cells and the transport was saturable, with a Km of 14.8 mM and a Vmax of 19.1 nmol min-1 microliters of cell water-1. By 31P nuclear magnetic resonance (NMR) spectroscopy, both PALA and phosphonoacetate were shown to have been metabolized in all isolates of H. pylori studied. A main metabolic end product was identified as inorganic phosphate, suggesting the presence of an enzyme activity which cleaved the carbon-phosphorus (C-P) bonds. The kinetics of phosphonate group cleavage was saturable, and there was no evidence for substrate inhibition at higher concentrations of either compound. C-P bond cleavage activity was temperature dependent, and the activity was lost in the presence of the metal chelator EDTA. Other cleavages of PALA were observed by 1H NMR spectroscopy, with succinate and malate released as main products. These metabolic products were also formed when N-acetyl-L-aspartate was incubated with H. pylori lysates, suggesting the action of an aspartase. Studies of the cellular location of these enzymes revealed that the C-P bond cleavage activity was localized in the soluble fraction and that the aspartase activity appeared in the membrane-associated fraction. The results suggested that the two H. pylori enzymes transformed the inhibitor into noncytotoxic products, thus providing the bacterium with a mechanism of resistance to PALA toxicity which appears to be unique.

Metronidazole resistance and microaerophily in Campylobacter species

Metronidazole is active against most anaerobic organisms and is also used in the treatment of the microaerophilic bacterium Helicobacter pylori. Resistance to metronidazole is uncommon in most anaerobic organisms, but it is increasingly prevalent in H. pylori. Previously we have suggested that metronidazole resistance in H. pylori is inherent in the microaerophilic nature of the organism and therefore would be present in other microaerophiles such as Campylobacter. Short periods of anaerobiosis caused metronidazole-resistant (MtrR) strains of Campylobacter spp. to become sensitive to metronidazole. Under microaerophilic conditions, cultures of the MtrR mutant Campylobacter coli R1 at bacterial cell densities of greater than 10(8) cfu/ml lost viability, whereas no loss in viability was observed in cultures at cell densities of less than 10(8). The MtrS C. coli strain lost viability at all cell densities. Comparisons of NAD(P)H oxidase activity between MtrS and MtrR strains indicated that the MtrS C. coli strain contained fourfold higher NADH oxidase activity and twofold higher NADPH oxidase activity than did the MtrR Campylobacter strains. These results show that MtrR Campylobacter spp. display resistance characteristics similar to those of H. pylori, suggesting that the resistance mechanism is a phenomenon of the microaerophilic nature of these bacteria.

Characterization of fumarate transport in Helicobacter pylori

The fumarate transport system of the bacterium Helicobacter pylori was investigated employing radioactive tracer analysis. The transport of fumarate at micromolar concentrations was saturable with a KM of 220 +/- 21 micron and Vmax of 54 +/- 2 nmole/min/mg protein at 20 degrees C, depended on temperature between 4 and 40 degrees C, and was susceptible to inhibitors, suggesting the presence of one or more fumarate carriers. The release of fumarate from cells was also saturable with a KM of 464 +/- 71 micron and Vmax of 22 +/- 2 nmol/min/mg protein at 20 degrees C. The rates of fumarate influx at millomolar concentrations increased linearly with permeant concentration, and depended on the age of the cells. The transport system was specific for dicarboxylic acids suggesting that fumarate is taken up via dicarboxylate transporters. Succinate and fumarate appeared to form an antiport system. The properties of fumarate transport were elucidated by investigating the effects of amino acids, monovalent cations, pH and potential inhibitors. The results provided evidence that influx and efflux of fumarate at low concentrations from H. pylori cells was a carrier-mediated secondary transport with the driving force supplied by the chemical gradient of the anion. The anaerobic C4-dicarboxylate transport protein identified in the genome of the bacterium appeared to be a good candidate for the fumarate transporter.

An investigation of the molecular basis of the spontaneous occurrence of a catalase-negative phenotype in Helicobacter pylori

BACKGROUND

The discovery of a highly active catalase in Helicobacter pylori that in some strains may lose its activity has generated strong scientific interest. We have characterized a spontaneous catalase-negative isolate of H. pylori (UNSW-RU1) and sequenced katA in the parent strain and the promoters of both phenotypes as a prelude to understanding the genetic processes leading to the failure to express catalase.

MATERIALS AND METHODS

Protein extracts from both phenotypes were examined for catalase on 2D-PAGE and analyzed by Western blot-based immuno-analysis. Presence of catalase mRNA was detected by Northern blot. Hi-Fidelity PCR was used to sequence the katA promoter while katA was sequenced using cycle-sequencing. The transcription start site was located by primer extension.

RESULTS

Catalase protein was absent in UNSW-RU1 (KatA-) by 2D-PAGE and Western blot, as was catalase mRNA by Northern blot, indicating that the cause of the KatA- phenotype was at the level of transcription. No mutations were found in the promoter region of the KatA- isolate. The transcription start site was identified 55 bp upstream of the ATG site and putative RNA polymerase binding sites were mapped at "-10" and "-35". A Fur box was identified 181 bp upstream of the transcription start site. The sequences of an 876 bp ORF and a 366 bp Escherichia coli phnA homologue were identified.

CONCLUSIONS

The UNSW-RU1 (KatA-) phenotype does not express KatA or transcribe katA. The absence of defects in its promoter and a large part of its ORF indicates that loss of activity may be due to a mutation in an accessory gene essential for catalase expression, or to the binding of a repressor preventing katA transcription.

A low rate of reinfection following effective therapy against Helicobacter pylori in a developing nation (China)

BACKGROUND & AIMS

In developed countries, reinfection after successful eradication of Helicobacter pylori appears unusual. High prevalences of H. pylori in developing countries may result in high reinfection rates. The aim of this study was to determine the rate of reinfection and ulcer recurrence in Chinese patients cured of H. pylori and duodenal ulcer disease.

METHODS

One hundred eighty-four patients with duodenal ulcer disease shown by endoscopic examination (1 month) and 14C-urea breath test (3 months) after termination of treatment to have cleared their H. pylori were investigated. Patients were followed up by endoscopy (12 and 24 months) and breath test (6, 9, 12, 18, and 24 months). H. pylori status at endoscopic examination was determined by rapid urease, histology, and culture. In reinfected patients, random amplification of polymorphic DNA fingerprinting was used to compare isolates before and after therapy.

RESULTS

Four patients were reinfected with H. pylori over 24 months (3 within 6 months and 1 at 24 months; average annual recurrence rate, 1.08%). Fingerprinting of isolates from 3 patients showed 1 patient (6 months) to have identical strains and the remainder to have nonidentical strains before and after treatment. Ulcer relapse occurred in 6 patients (4 H. pylori positive).

CONCLUSIONS

Reinfection with H. pylori is rare in developing countries where treatment is effective.

The mode of action of metronidazole in Helicobacter pylori: futile cycling or reduction?

The effects of metronidazole on catalase-positive and spontaneous catalase-negative mutants of Helicobacter pylori were studied to investigate whether the action of metronidazole on this microaerophilic organism occurs by reactive oxygen species generated by futile cycling or by the reduction of metronidazole to its active form. Increased sensitivity would be expected to occur in catalase-negative mutants if the mode of action of metronidazole was mediated through reactive oxygen species that may result from futile cycling of metronidazole. Two strains, RU1 and N6, were found to mutate spontaneously to a catalase-negative phenotype. The catalase-positive strain RU1(KatA+) and its catalase-negative counterpart RU1(KatA-) were sensitive to metronidazole, with MICs of 0.5 mg/L. The metronidazole-sensitive strain RU1(KatA-) lost viability at a rate similar to the parent RU1(KatA+) strain in the presence of 10 mg/L of metronidazole. Stable resistance to metronidazole was induced in RU1(KatA+) and RU1(KatA-) by passaging these strains in the presence of metronidazole. The catalase-positive and catalase-negative strains, N6(KatA+) and N6(KatA-), were resistant to metronidazole, with MICs of 96 mg/L. These observations indicated that the presence or absence of catalase activity did not affect the susceptibility of strains to metronidazole. The metabolism of metronidazole by H. pylori was investigated by 14N-NMR spectroscopy. Metronidazole was reduced in sensitive, catalase-positive and catalase-negative strains. Metronidazole-resistant cells reduced the 5-nitroimidazole more slowly, suggesting that resistance is achieved through the prevention or inhibition of metronidazole reduction.

Purine metabolism and the microaerophily of Helicobacter pylori

The requirements for purine nucleotide synthesis, the effects of purine analogues, and the metabolism of adenine in the bacterium Helicobacter pylori were investigated employing cell culture techniques and one-dimensional NMR spectroscopy. Bacterial cells grew and proliferated in media lacking preformed purines, indicating that H. pylori can synthesize purine nucleotides de novo to meet its requirements. Blocking of this pathway in the absence of sufficient preformed purines for salvage nucleotide synthesis led to cell death. Analogues of purine nucleobases and nucleosides taken up by the cells were cytotoxic, suggesting that salvage routes could be exploited for therapy. Adenine or hypoxanthine were able to substitute for catalase in supporting cell growth and proliferation, suggesting a role for these bases in maintaining the microaerophilic conditions essentially required by the bacterium.

Catalase, a novel antigen for Helicobacter pylori vaccination

The efficacy of an orogastric vaccine comprised of purified Helicobacter pylori catalase plus the mucosal adjuvant cholera toxin (CT) was examined with both the Helicobacter felis and H. pylori mouse models with BALB/c mice. Native H. pylori catalase (200 microg) plus CT was initially used as a vaccine antigen in the H. felis mouse model and protected 80% (8 of 10) of the challenged animals, while all control animals were infected (20 of 20). In a follow-up experiment, recombinant H. pylori catalase plus CT was used for immunization, and groups of mice were challenged with the Sydney strain of H. pylori. Immunization with recombinant catalase protected a significant proportion (9 of 10) of the mice from H. pylori challenge, indicating that this enzyme should be considered as a candidate for a future vaccine. This study provides the first available data on the efficacy of protective immunization with the new Sydney strain of H. pylori in a mouse model. These data also provide indirect evidence that proteins which are normally intracellular, such as catalase, may be present on the surface of H. pylori and thus may provide targets for immunization.

In situ properties of Helicobacter pylori aspartate carbamoyltransferase

The kinetic and regulatory properties of aspartate carbamoyltransferase (ACTase) of the human pathogen Helicobacter pylori were studied in situ in cell-free extracts. The presence of enzyme activity was established by identifying the end product as carbamoylaspartate using nuclear magnetic resonance spectroscopy. Activity was measured in all strains studied, including recent clinical isolates. Substrate saturation curves determined employing radioactive tracer analysis or a microtiter colorimetric assay were hyperbolic for both carbamoyl phosphate and aspartate, and there was no evidence for substrate inhibition at higher concentrations of either substrate. The apparent Km were 0.6 and 11.6 mm for carbamoyl phosphate and aspartate, respectively. Optimal pH and temperature were determined as 8.0 and 45 degrees C. Activity was observed with the l- but not the d-isomer of aspartate. Succinate and maleate inhibited enzyme activity competitively with respect to aspartate. The carbamoyl phosphate analogues acetyl phosphate and phosphonoacetic acid inhibited activity in a competitive manner with respect to carbamoyl phosphate. With limiting carbamoyl phosphate purine and pyrimidine nucleotides, tripolyphosphate, pyrophosphate, and orthophosphate inhibited competitively at millimolar concentrations. Ribose and ribose 5-phosphate at 10 mm concentration showed 20 and 35% inhibition of enzyme activity, respectively. N-Phosphonoacetyl-l-aspartate (PALA) was the most potent inhibitor studied, with 50% inhibition of enzyme activity observed at 0.1 microM concentration. Inhibition by PALA was competitive with carbamoyl phosphate (Ki = 0.245 microM) and noncompetitive with aspartate. The kinetic and regulatory data on the activity of the H. pylori enzyme suggest it is a Class A ACTase, but with some interesting characteristics distinct from this class.

Influence of a proton pump inhibitor-based therapy on Helicobacter pylori strain selection

The influence of the proton pump inhibitor lansoprazole on strain diversity in Helicobacter pylori infected patients was investigated. Multiple isolates of Helicobacter pylori obtained pre- and post-therapy from gastric antral and body biopsies in 22 patients were compared using the random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) for analysis. Post-therapy strains exhibiting novel RAPD-profiles were found in 5 of 22 patients (4 of 11 patients treated with lansoprazole alone and 1 of 11 patients treated with lansoprazole plus amoxicillin). Proton pump inhibition may affect the microecology of the stomach by influencing the colonisation patterns of specific strains.

Genetic relationship among isolates of Helicobacter pylori: evidence for the existence of a Helicobacter pylori species-complex

We investigated the population genetics of 23 isolates of H. pylori by allozyme electrophoresis using 16 enzyme loci. Isolates were obtained from adult patients of whom 48% were of Greek extraction. Eight patients (35%) had an active duodenal ulcer. Allelic variation per loci ranged from 2 to 11 alleles. Four major genetic clusters were apparent, having > 75% fixed genetic differences. There was no distinct clustering (clonal structure) on the basis of the geographical origin of the persons from whom isolates were obtained, indicating that this bacterium has not recently jumped a species barrier into humans. Isolates associated with ulcer disease were not monophyletic, with isolates from ulcer patients being found in phylogenetically diverse branches of the dendogram derived from the data. Based on the genetic diversity of H. pylori isolates, we propose that isolates should be classified as belonging not to a single species but to a 'Helicobacter pylori species-complex'.

Lansoprazole and amoxycillin: observations on the treatment of Helicobacter pylori infection

Symptomatic patients (n = 101) with Helicobacter pylori infection were enrolled into a double-blind, double-dummy study to assess the efficacy of lansoprazole plus amoxycillin in the treatment of H. pylori infection. Patients were randomized to either lansoprazole 30 mg once daily (days 0-28) together with placebo (matched to amoxycillin) three times a day (days 0-14) followed by either placebo or amoxycillin 500 mg three times daily (days 15-28). Biopsy specimens for culture and histology were collected on days 0 and 56 or upon symptomatic relapse. Blood for serology was collected at days 0, 56 and 168. A [14C]-urea breath test was performed on day 168. Eighty-one (80.2%) patients completed the 56 day assessment. Of patients treated with lansoprazole plus amoxycillin, 35.1% (13/37) were cured of infection as assessed at day 56 (26.5% on an intention-to-treat basis), compared with 4.8% (2/42) of the placebo group (4% on an intention-to-treat basis). Recrudescence/re-infection occurred in one patient upon re-evaluation at day 168. Analysis of prognostic factors indicated that smoking and alcohol intake had little impact on the treatment outcome. Inflammation (both acute and chronic) improved in patients treated with lansoprazole plus amoxycillin. The relatively low efficacy of the treatment may relate to a single daily dose of lansoprazole (30 mg) being prescribed, treatment with amoxycillin being commenced 2 weeks after the initiation of lansoprazole or accurate assessment of treatment efficacy (both antral and body biopsy specimens taken).

The urea cycle of Helicobacter pylori

The presence and activities of the enzymes of the urea cycle in the bacterium Helicobacter pylori were investigated employing one- and two-dimensional NMR spectroscopy and radioactive tracer analysis. Cell suspensions, lysates and membrane preparations generated L-ornithine and ammonium at high rates in incubations with L-arginine, indicating the presence of arginase activity. Anabolic ornithine transcarbamoylase (OTCase) activity was identified by the formation of heat-stable products in incubations of cell-free extracts with ornithine and radiolabelled carbamoyl phosphate. The heat-labile product that resulted from incubations of cell-free extracts with citrulline radiolabelled in the guanidino moiety revealed the presence of catabolic OTCase activity. Argininosuccinate formation and catalysis indicated the presence of argininosuccinate synthetase and argininosuccinase activities. The findings suggested that H. pylori has a urea cycle which acts as an effective mechanism to extrude excess nitrogen from cells.

Serological response to specific Helicobacter pylori antigens: antibody against CagA antigen is not predictive of gastric cancer in a developing country

OBJECTIVES

In symptomatic patients resident in developed countries, a high prevalence of antibody to the cytotoxin-associated antigen (CagA) of Helicobacter pylori has been linked to the development of peptic ulcer disease and gastric cancer. This association has not been examined in developing countries, nor in asymptomatic subjects resident in either developed or developing countries. The aim of this study was to examine the seroprevalence of antibody to the CagA antigen; as well as other specific H. pylori antigens in symptomatic and asymptomatic individuals resident in Australia and China.

METHODS

The Helico-blot 2.0 Western blot system was used for the detection of antibodies to specific antigens of H. pylori in sera obtained from the following H. pylori-positive groups: 19 Australian blood donors, 96 Australian nonulcer dyspepsia patients, 29 Australian duodenal ulcer patients, 35 asymptomatic Chinese subjects, and 48 Chinese gastric cancer patients.

RESULTS

Nine antigens were commonly recognized by sera from Australian and Chinese subjects. These antigens were of molecular mass 19.5 kDa, 26.5 kDa, 35 kDa, 45 kDa, 60 kDa, 89 kDa (VacA), 116 kDa (CagA), and 180 kDA. A significant association between the prevalence of antibody to the CagA antigen and duodenal ulcer disease was observed in Australian subjects; however, no association between the prevalence of antibody to the CagA antigen and gastric cancer was found in Chinese subjects. In subjects from both countries, a significant association was found between antibody to the 30-kDa and 45-kDa antigens and more serious gastroduodenal disease.

CONCLUSION

The results of this study suggest that the cagA gene is not associated with the development of more serious gastroduodenal disease; however, it cannot be ruled out that this gene may be an important but insufficient factor in some disease processes.

Multiple strain colonization and metronidazole resistance in Helicobacter pylori-infected patients: identification from sequential and multiple biopsy specimens

Helicobacter pylori strain diversity was investigated in infected persons by collection of multiple biopsies before and after therapy failure. It was demonstrated by random amplification of polymorphic DNA polymerase chain reaction that patients may be infected with a mixed population of H. pylori strains. Most patients were colonized with a predominant strain accompanied by up to 5 variant strains. The use of antimicrobials resulted in an altered distribution of the strains present, but the predominant strain usually remained. Patients may be infected with a mixed population of metronidazole-sensitive and -resistant strains at one time, with metronidazole-based therapy selectively enriching for a resistant population.

Antigen recognition during progression from acute to chronic infection with a cagA-positive strain of Helicobacter pylori

We have previously published two reports on acute infection with Helicobacter pylori, one of an adult male and one of a family of four. In the present study, we have isolated H.pylori from each of twin boys in the family and compared these by use of random amplified polymorphic DNA PCR. In addition, we have monitored the antibody response over time of the family and the adult male by Western blotting (immunoblotting) with two different strains of H. pylori as the antigen and by use of a commercial kit. The acutely infected twin boys were infected by an identical strain of H. pylori. The twin boys responded to antigens of 19, 26.5, and 29 kDa 30 days after the initial diagnosis, with recognition of 43-to 49-, 66-, 69-, and 87-kDa antigens by day 63. One twin responded to the CagA antigen on day 63, whereas the other responded on day 857. Antibody to the CagA antigen was not detected by use of the infecting strain, UNSW-RU1. Investigation of UNSW-RU1 revealed the presence of cagA. In two acutely infected adults (one, the father of the boys), the initial response to a 45-kDA antigen was later followed by responses to 19-, 29-, 49-, 60-, 77-, and 84-kDa antigens. Sera from the twins' younger sister, born 17 months after the twins acute episode, indicated that she also had become infected. This report supports intrafamilial transmission of H. pylori. Initial antibody responses in the children were to small-molecular-size antigens; in the adults, the initial responses were to larger-molecular-size antigens. The pattern of the serological response differs according to the antigen used. This has implications in regard to international data comparisons.

Acetyl-CoA carboxylase activity in Helicobacter pylori and the requirement of increased CO2 for growth

A biotinylated acetyl-CoA carboxylase from the microaerophilic bacterium Helicobacter pylori was partially purified and characterized. The approximate molecular mass of the native enzyme was estimated at 235 kDa by native PAGE. A single band corresponding to approximately 24 kDa was detected by SDS-PAGE, suggesting that the native enzyme is a multi-protein complex. The protein was isolated from the soluble fraction of the cell. Catalytic activity was acetyl-CoA-dependent and inhibited by avidin but unaffected by avidin pretreated with excess biotin. The end-product of the reaction was identified as malonyl-CoA and the reaction was shown to be reversible by NMR spectroscopy. The activity of the enzyme was 0.29 mumol min-1 (mg protein)-1. The Vmax for bicarbonate was calculated at 0.73 mumol min-1 (mg protein)-1, and the affinity of the enzyme for this substrate was relatively low, with an apparent Km of 16.6 mM. These data provide the first evidence of a possible physiological role for the requirement of high levels of CO2 for growth in vitro of this bacterium.

Aminoacid utilization by Helicobacter pylori

Utilization of aminoacids during growth by laboratory adapted and wild type Helicobacter pylori strains was investigated employing nuclear magnetic resonance spectroscopy and aminoacid analysis. All H. pylori strains tested showed growth rates with doubling times of approx. 11.5 hr in liquid cultures with semi-defined media or with defined aminoacid broth without carbohydrates. Fast utilization of several aminoacids at rates between 80 and 250 microM/hr was observed in culture broths inoculated with approx. 10(7) cells/ml; and acetate, formate and succinate accumulated as catabolic products in the growth media. Suspensions of bacterial cells and lysates in isotonic solutions converted arginine, asparagine, aspartate, glutamine, and serine used as sole substrates at significant rates; and under these conditions the principal metabolic products observed were acetate, formate, succinate and lactate. The findings of the study indicated that H. pylori can survive employing aminoacids as the basic nutrients, and suggested some of these metabolites were utilized via fermentative pathways with common characteristics to those found in anaerobes.

Fumarate reductase: a target for therapeutic intervention against Helicobacter pylori

The potential of fumarate reductase as a therapeutic target against the human pathogen Helicobacter pylori was investigated by studying the cytotoxicity of morantel, oxantel, and thiabendazole, known to inhibit the enzyme in parasitic worms. Nuclear magnetic resonance spectroscopy was employed to investigate the effects of the inhibitors on the fumarate reductase activity of laboratory-adapted and wild-type bacterial strains. Production of succinate from fumarate in H. pylori cells was inhibited by morantel, oxantel, and thiabendazole. Cell growth and viability techniques were used to examine the bacteriostatic and bactericidal effects of the three anthelmintics. Each of the antiparasites arrested growth and produced cell death in liquid cultures, although the minimal inhibitory and bactericidal concentrations of these compounds are such that they would not be of therapeutic use. The strength of the effects as measured by minimal inhibitory and bactericidal concentrations was oxantel > thiabendazole > morantel. The findings suggested that fumarate reductase is an essential component of the metabolism of H. pylori and as such constitutes a possible target for therapeutic intervention in the treatment of the bacterium.

Gastric atrophy and regional variation in upper gastrointestinal disease

OBJECTIVE

To compare the upper gastrointestinal disease profiles of Helicobacter pylori-infected patients drawn from two distinct regions of China, one with a low incidence of gastric cancer (Guangzhou) and the other with a high incidence of gastric cancer (Lanzhou). The age-standardized prevalence of H. pylori within the populations of these two cities was similar (approximately 56%). In these patient groups, the prevalence of different gastrointestinal disease states and the occurrence and severity of gastritis, gastric atrophy, and intestinal metaplasia were compared.

METHODS

This study was based on consecutive patients: 265 from Guangzhou and 275 from Lanzhou. The grading of gastritis and the detection of H. pylori was determined by histology using the "Sydney System".

RESULTS

The ratio of cases of duodenal to gastric ulceration for the two cities was: Guangzhou 14:1 and Lanzhou 3:1. Gastric cancer was more prevalent in the patients from Lanzhou (9.8%) than from Guangzhou (3%). In nonulcer dyspepsia patients from Guangzhou, gastritis was predominantly antral, whereas, in Lanzhou, gastritis was predominantly uniform. The amount and severity of atrophy was significantly greater in Lanzhou compared with Guangzhou.

CONCLUSIONS

The prevalence of atrophy, rather than age of acquisition and prevalence of H. pylori infection, appears to be a marker of the major upper gastrointestinal disease profiles of a region. Development of atrophy, although apparently related to H. pylori infection, may be a multifactorial condition. Differences in diet, as seen between Guangzhou and Lanzhou, may be important in this regard. Understanding the factors leading to the development of atrophy may enhance our understanding of processes leading to gastric malignancy.

Characterisation of glucose transport in Helicobacter pylori

The nature of the glucose transport system in the bacterium Helicobacter pylori was investigated employing radioactive tracer analysis. Fast D-glucose uptake was demonstrated by using two methods of measuring glucose transport. The transport of 2-deoxy-D-glucose was inhibited competitively by D-glucose; and the efflux of 2-deoxy-D-glucose from cells also was affected by the presence of D-glucose. The transport of 2-deoxy-D-glucose was saturable with a Km of 4.8 mM and Vmax of 146.6 pmol (microliter cell water)-1 at 20 degrees C. The transport was temperature-dependent with energies of activation of 6.8 and 51.0 kJ mol-1 for 0.2 and 20 mM 2-deoxy-D-glucose, respectively. The temperature dependence and saturable nature of transport suggested the presence of one or more glucose carriers. The substrate specificity of the transport system was studied by measuring the effects of mono- and disaccharides on the rates of transport of the glucose analogue. The most significant inhibitory effects were obtained with D-galactose and L-arabinose. Lack of transport inhibition by L-glucose established the stereospecificity of the transporters for the D-isomer of glucose. Higher rates of 2-deoxy-D-glucose transport were measured in the presence of sodium ions than for other monovalent cations, and the presence of amiloride inhibited transport of the monosaccharide. No inhibition was observed with cytochalasin B, phloretin or phloridzin. The results suggested the existence of specific D-glucose transporters and that the glucose transport system of H. pylori is significantly different from other known bacterial transporters.

Helicobacter pylori associated with a high prevalence of duodenal ulcer disease and a low prevalence of gastric cancer in a developing nation

This study examines the relationship between Helicobacter pylori infection and peptic ulcer disease and gastric cancer--in particular, the presence or absence of bacteria, the grading of gastritis, and the degree of inflammation in the antral and oxyntic mucosae. The grading of gastritis and the detection of H pylori were determined by histology using the Sydney system. Of the 1006 patients examined, 34.5% had duodenal ulcer disease, 3.5% gastric ulcer disease, and 2% with coexistent ulceration. Most patients (50.2%) were classified as having non-ulcer dyspepsia. Altogether 2.4% of patients had gastric cancer and two further patients had carcinoma in the gastric stump. Of the ulcer disease patients, 87.2% had histological evidence of H pylori infection. After patients who had taken antibiotics or bismuth compounds in the preceding four weeks were excluded, 98.9% of the duodenal ulcer disease, 100% of the gastric ulcer disease, and 100% of the coexistent ulcer disease patients had evidence of H pylori infection. In patients with gastric cancer who had not taken antimicrobial agents in the four weeks before endoscopy, 83.3% had evidence of H pylori infection. Thus, there was a high rate of duodenal ulcer disease and a low rate of gastric ulcer disease in southern China, an area of low gastric cancer mortality. There was a specific topographical relationship between H pylori, the histological response, and gastroduodenal disease. Our data suggest that the status of a nation as either 'developed' or 'developing' can not be used to predict the upper gastrointestinal disease profile of its population.

Salvage synthesis of purine nucleotides by Helicobacter pylori

The incorporation of purine nucleotide precursors into Helicobacter pylori and the activities of enzymes involved in nucleotide salvage biosynthetic pathways were investigated by radioactive tracer analysis and nuclear magnetic resonance spectroscopy. The organism took up the nucleobases adenine, guanine and hypoxanthine, and the nucleosides adenosine, guanosine and deoxyadenosine. Any incorporation of deoxyguanosine by the cells was below the detection limits of the methods employed. The activities of adenine-, guanine- and hypoxanthine-phosphoribosyl transferases were established. The bacterium showed high levels of adenosine and guanosine nucleosidase activities and lesser activity for deoxyadenosine; no hydrolysis of deoxyguanosine was detected. Phosphorylase activities were not observed with any of the nucleosides. Phosphotransferase activities with similar rates were demonstrated for adenosine, guanosine and deoxyadenosine; and a weaker activity was detected for deoxyguanosine. No nucleoside kinase activities were observed with any of the nucleosides. The presence of adenylate kinase was established, but no guanylate kinase activity was observed. The study provided evidence for the presence in H. pylori of salvage pathways for the biosynthesis of purine nucleotides.

Association of Helicobacter pylori with gastric cancer and observations on the detection of this bacterium in gastric cancer cases

OBJECTIVE

The aim of the present study was to assess the prevalence of Helicobacter pylori infection in Chinese patients with advanced gastric cancer, to compare this with a matched control population, and to identify factors that may effect the detection of H. pylori in patients with gastric cancer.

METHODS

Fifty-one patients with advanced gastric cancer and 102 age/sex-matched controls were included in the study. For the detection of H. pylori, both biopsy specimens and sera were collected from the patients, whereas only sera were collected from the controls. A strong association was shown between H. pylori and both intestinal and diffuse type gastric cancer. Antibiotic intake in the month before endoscopic examination, the site of collection of biopsy specimens, and tumor size were identified as factors that may reduce the histological detection of H. pylori in gastric cancer patients.

CONCLUSIONS

These data provide supporting evidence of an association between H. pylori infection and gastric cancer and indicate that, in certain circumstances, histological evaluation of H. pylori infection in gastric cancer cases may be less reliable than serological evaluation.

Hepatitis A and evidence against the community dissemination of Helicobacter pylori via feces

Seroprevalence data from 1501 subjects was used to test the hypothesis that Helicobacter pylori may be transmitted by the fecal-oral route. Antibody to hepatitis A virus was used as a marker of fecal-oral exposure. Of the 1501 subjects, 35.5% were seropositive for both H. pylori and hepatitis A, 19.1% were seronegative for both, 36.5% were seropositive for hepatitis A only, and 8.8% were seropositive for H. pylori only. Cross-sectional data from rural areas supported an association between hepatitis A and H. pylori. However, in the urban area there was no evidence of hepatitis A infection in persons < 10 years old, yet the seroprevalence of H. pylori was high in this group (approximately 32%). From our data, we suggest that communitywide fecal-oral spread of H. pylori may be of limited importance.

The Entner-Doudoroff pathway in Helicobacter pylori

Evidence for the presence of the enzymes of the Entner-Doudoroff pathway in Helicobacter pylori was obtained using 1H and 31P nuclear magnetic resonance spectroscopy. Bacterial lysates generated 6-phosphogluconate and NADH or NADPH in incubations with glucose-6-phosphate and NAD+ or NADP+, indicating the presence of glucose-6-phosphate dehydrogenase activities. Formation of pyruvate was observed in time courses of incubations of bacterial lysates with 6-phosphogluconate as the only substrate, suggesting the presence of 6-phosphogluconate dehydratase and 2-keto-3-deoxy-6-phosphogluconate aldolase activities. The existence of these enzymes and of triose phosphate isomerase was confirmed by observing the appearance of dihydroxyacetone phosphate in time courses of bacterial lysates incubated with 6-phosphogluconate. Aldolase activity was measured by the production of pyruvate and dihydroxyacetone phosphate in lysates incubated with 2-keto-3-deoxy-6-phosphogluconate as the sole substrate. Dehydrogenase, dehydratase and aldolase activities were observed in several bacterial strains including wild types from fresh isolates. Kinetic parameters were measured for the three activities. The cellular location of the enzymes was investigated by comparing the activities measured in the pellet and supernatant fractions obtained by centrifugation of lysate suspensions. The concentration of compounds causing 50% inhibition of enzyme activity was determined from dose-response curves. The data suggested the presence of two glucose-6-phosphate dehydrogenases linked to NAD+ and NADP+ activities. Using inhibitors differences between the H. pylori and mammalian KDPG aldolases were detected. The presence of these enzyme activities in H. pylori provided evidence for the existence of the Entner-Douderoff pathway in the bacterium.

Pyruvate metabolism in Helicobacter pylori

The metabolism of pyruvate by Helicobacter pylori was investigated employing one- and two-dimensional 1H and 13C nuclear magnetic resonance spectroscopy. Generation of pyruvate from L-serine in incubations with whole cell lysates indicated the presence of serine dehydratase activity in the bacterium. Pyruvate was formed also in cell suspensions and lysates from phosphoenol pyruvate. Metabolically competent cells incubated aerobically with pyruvate yielded alanine, lactate, acetate, formate, and succinate. The production of alanine and lactate indicated the presence of alanine transaminase and lactate dehydrogenase activities, respectively. Accumulation of acetate and formate as metabolic products provided evidence for the existence of a mixed-acid fermentation pathway in the microorganism. Formation of succinate suggested the incorporation of the pyruvate carbon skeleton into the Kreb's cycle. Addition of pyruvate to various liquid culture media did not affect bacterial growth or loss of viability. The variety of products formed using pyruvate as the sole substrate showed the important role of this metabolite in the energy metabolism of H. pylori.

De novo synthesis of pyrimidine nucleotides by Helicobacter pylori

The incorporation of pyrimidine nucleotide precursors into Helicobacter pylori and the activities of enzymes involved in their synthetic pathways were investigated by radioactive tracer analysis and 31P nuclear magnetic resonance spectroscopy. The bacterium was found to take up aspartate and bicarbonate and to incorporate carbon atoms from these precursors into its genomic DNA. Orotate, an intermediate of de novo pyrimidine biosynthesis, and uracil and uridine, precursors for pyrimidine pathways, were also incorporated by the micro-organism. Radiolabelled substrates were used to assess the activities of aspartate transcarbamoylase, orotate phosphoribosyltransferase, orotidylate decarboxylase, CTP synthetase, uracil phosphoribosyltransferase, thymidine kinase and deoxycytidine kinase in bacterial lysates. The study provided evidence for the presence in H. pylori of an operational de novo pathway, and a less active salvage pathway for the biosynthesis of pyrimidine nucleotides.

Lack of protection against gastric Helicobacter infection following immunisation with jack bean urease: the rejection of a novel hypothesis

The common mucosal immune system was stimulated by oral immunisation with jack bean urease and the adjuvant cholera toxin. A high level of local antibody and serum antibody was induced in mice following hyperimmunisation with this combination. No cross-reacting antibody was found against either Helicobacter pylori or Helicobacter felis. No protection was observed against oral challenge of immunised mice with living H. felis thus disproving the interesting hypothesis of Pallen and Clayton that plant urease might induce a protective immunity against helicobacter infection.

Glucose utilization and lactate production by Helicobacter pylori

The transport and incorporation of D-glucose into the human pathogen Helicobacter pylori was investigated employing radioactive tracer analysis and 1H and 13C nuclear magnetic resonance spectroscopy. The bacterium was found to utilize D-glucose contrary to the accepted view that it cannot catabolize carbohydrates. Under the experimental conditions employed, the rate of transport of [14C]glucose was 3.24 mmol min-1 (g protein)-1, and the rate of incorporation into the cellular mass was 1.06 mumol h-1 (g protein)-1. The utilization of [13C]glucose showed biphasic characteristics with a slower initial period followed by a phase with a rate of utilization at least an order of magnitude faster. The apparent rates of decline of glucose levels during both phases varied between strains and depended on the growth conditions of the bacteria prior to harvesting. The main product of glucose catabolism was identified as lactate. These findings provide new perspectives into the physiology of H. pylori and have implications for the active search to develop appropriate therapies for the micro-organism.

Phospholipase activity of Helicobacter pylori and its inhibition by bismuth salts. Biochemical and biophysical studies

In this study we measured phospholipase A (PLA) and C (PLC) activity of media filtrates and French Press lysates of the gastritis-inducing bacteria Helicobacter pylori. We report here that both H. pylori lysates and filtrates contain PLA1, PLA2, and C enzymes, which readily hydrolyze a radiolabeled dipalmitoylphosphatidylcholine (DPPC) and phosphorylcholine substrates, respectively. The specific activity of both PLA and C enzymes were greatest in the 6.5-7.0 and 8.4-8.8 pH ranges, respectively. Colloidal bismuth subcitrate (CBS) induced a dose-dependent inhibition of PLA2 and C activity of both H. pylori lysates and filtrates. This inhibitory effect of CBS on PLA2 was antagonized in a dose-dependent fashion by the addition of CaCl2 to the incubation mixture, suggesting that calcium and bismuth may be competing for the same site on the enzyme. In contrast, the ability of bismuth salts to inhibit PLC activity of H. pylori lysates was not antagonized by CaCl2. Employing a biophysical assay system for surface wettability, it was determined that H. pylori lysates had the capacity to remove a synthetic phospholipid monolayer off a glass in a dose-dependent fashion. This ability of the bacterial lysates to catalyze the transformation of a hydrophobic surface to a wettable state was significantly attenuated in the presence of bismuth salts. Our experimental results are, therefore, consistent with the possibility that H. pylori colonization compromises the stomach's barrier to acid by eroding a phospholipid lining, possibly a monolayer, on the surface of the gastric mucus gel and that this process is blocked in response to bismuth therapy.

Fumarate catabolism in Helicobacter pylori

The metabolism of fumarate by Helicobacter pylori was investigated employing one- and two-dimensional 1H and 13C nuclear magnetic resonance spectroscopy. Metabolically competent cells generated malate and succinate from fumarate as the sole substrate indicating the presence of fumarase and fumarate reductase activities in the bacterium. In incubations of fumarate with cell lysates accumulation of lactate, acetate, formate and alanine was observed after the initial production of malate and succinate. The results indicate the existence of active fumarate catabolism in H. pylori and suggest the possibility of an ATP generating mechanism which may play an important role in the bioenergetics of the bacterium.

Fluorinated probes to measure carboxylesterase activities using 19F NMR spectroscopy: application to erythrocytes and Helicobacter pylori

Eight fluorinated compounds were tested as putative probes to measure carboxylesterase activity employing 19F nuclear magnetic resonance spectroscopy. The method takes advantage of the sensitivity of fluorine resonances to the changes in the chemical bonding in the covalent structures where they are located. Determination of the kinetic parameters of ethyl fluoroacetate and diethyl fluoromalonate in hemolysates showed that these probes were well suited to study carboxylesterase activities in complex systems the potential of these probes for noninvasive applications was demonstrated in measurements of carboxylesterase kinetic parameters in intact erythrocytes. The presence of carboxylesterases was established in several strains of the bacterium Helicobacter pylori employing 19F nuclear magnetic resonance spectroscopy, and the kinetic parameters of these enzymes for ethyl fluoroacetate and diethyl fluoromalonate were measured.

Glucose phosphorylation in Helicobacter pylori

Saccharide kinase activities in Helicobacter pylori were investigated by incubating bacterial lysates with ATP and mono- or disaccharides and monitoring directly the appearance of phosphorylated products using 13C or 31P nuclear magnetic resonance spectroscopy. The monosaccharides employed included two trioses, two tetroaldoses, one tetroketose, five aldopentoses, two ketopentoses, five aldohexoses, three ketohexoses, and gluconic and glucuronic acids; the disaccharides studied were maltose, trehalose, cellobiose, sucrose, lactose, gentobiose, and melibiose. D-Glucose was the only sugar phosphorylated among all the carbohydrates examined. The kinase activity of lysates was studied by measuring the rates of formation of glucose 6-phosphate. The substrate specificity, the relatively high KM, and the absence of substrate inhibition suggested that the enzyme is a glucokinase rather than a hexokinase. Most of the glucose kinase activity was observed with the pellet fraction obtained by centrifugation, suggesting an association of the enzyme with the bacterial cell envelope.

Selection of the chimpanzee over the baboon as a model for Helicobacter pylori infection

Baboons (Papio sp.) and chimpanzees (Pan troglodytes) were screened for the presence of Helicobacter pylori. The gastric mucosae of the baboons were colonized by large spiral bacteria. However, a group of adult chimpanzees were identified that were free of spiral gastric bacteria, with five animals being recruited into an H. pylori challenge study. These animals were inoculated orogastrically with one of four strains of H. pylori and followed for up to 26 weeks. H. pylori was established in one of these animals during a primary challenge and in two other animals on secondary challenge. It was shown that the chimpanzee can be infected with H. pylori and that the inflammatory response in these animals mimics that seen in humans. Infection was marked by an antibody response to H. pylori-specific antigens in two animals. It was observed that H. pylori antibody-negative chimpanzees had no apparent infection by H. pylori or related bacteria. Thus serological screening of chimpanzees can be used to identify candidate animals for further evaluation.

Epidemiology of Helicobacter pylori in southern China: identification of early childhood as the critical period for acquisition

A large cross-sectional study to investigate the prevalence and possible modes of transmission of Helicobacter pylori was done in southern China. Serum samples (1727) were collected from Guangzhou city and three rural areas of Guangdong Province, and the prevalence of H. pylori infection was determined using an ELISA. Each subject completed a questionnaire. The overall prevalence of H. pylori infection was 44.2%; a significantly higher prevalence was found in Guangzhou (52.4%) than in the rural areas (38.6%). This difference was generally reflected in the group 0-5 years old, but the rate of increase in seroprevalence for H. pylori over 5 years of age was similar (1%/year). This study provides important new data on the acquisition of H. pylori, particularly in the early years of life, and shows that density of living conditions is a prime determinant in the acquisition of H. pylori.

Oxyntic and antral gastritis in the People's Republic of China: diagnosis and relationship to Helicobacter pylori

This study investigates the relationship between gastritis and Helicobacter pylori infection in the Chinese population. Particular focus was placed upon the grading of gastritis, using the recently developed "Sydney system." Five diagnostic procedures were used to establish H. pylori status, all of which were found to be highly sensitive and specific. Histological chronic gastritis was reported in 93/108 (86.1%) of the patients examined, H. pylori infection being present in 73/93 (78.5%), and in no patient with histologically normal mucosae. There was a relatively high incidence of idiopathic antral gastritis within the gastritic population, 20/93 (21.5%). In the H. pylori-positive group, 10/73 (13.7%) had pangastritis, 57/73 (78.1%) had pangastritis-antrum-predominant, and 6/73 (8.2%) had antral-only gastritis. The level of activity was significantly higher in the antrum; however, the distribution of bacteria between the antrum and body was not significantly different. There is a need for additional studies examining the specific topographical relationship between H. pylori, the histology, and gastroduodenal disease.