cag, a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors

The high-pathogenicity island of Yersinia enterocolitica Ye8081 undergoes low-frequency deletion but not precise excision, suggesting recent stabilization in the genome

Highly pathogenic strains of Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica are characterized by the possession of a pathogenicity island designated the high-pathogenicity island (HPI). This 35- to 45-kb island carries an iron uptake system named the yersiniabactin locus. While the HPIs of Y. pestis and Y. pseudotuberculosis are subject to high-frequency spontaneous deletion from the chromosome, we were initially unable to obtain HPI-deleted Y. enterocolitica 1B isolates. In the present study, using a positive selection strategy, we identified three HPI-deleted mutants of Y. enterocolitica strain Ye8081. In these three independent clones, the chromosomal deletion was not limited to the HPI but encompassed a larger DNA fragment of approximately 140 kb. Loss of this fragment, which occurred at a frequency of approximately 5 x 10(-7), resulted in the disappearance of several phenotypic traits, such as growth in a minimal medium, hydrolysis of o-nitrophenyl-beta-D-thiogalactopyranoside, Tween esterase activity, and motility, and in a decreased virulence for mice. However, no precise excision of the Ye8081 HPI was observed. To gain more insight into the molecular basis for this phenomenon, the putative machinery of HPI excision in Y. enterocolitica was analyzed and compared to that in Y. pseudotuberculosis. We show that the probable reasons for failure of precise excision of the HPI of Y. enterocolitica Ye8081 are (i) the interruption of the P4-like integrase gene located close to its right-hand boundary by a premature stop codon and (ii) lack of conservation of 17-bp att-like sequences at both extremities of the HPI. These mutations may represent a process of HPI stabilization in the species Y. enterocolitica.

Prevalence and genetic diversity of cagD, cagE, and vacA in Helicobacter pylori strains isolated from Japanese patients

BACKGROUND

Although cagD and cagE (cagDE) identified upstream of cagA have been shown to be involved in the induction of interleukin (IL)-8 expression, the relationship between cagDE status and gastroduodenal diseases still remains to be examined. Thus we investigated prevalence and genetic diversity of cagD, cagE, and vacA in Helicobacter pylori strains isolated from patients with peptic ulcer or gastritis.

METHODS

We analyzed 73 H. pylori strains isolated from Japanese patients (gastritis (GA), 15; gastric ulcer (GU), 28; duodenal ulcer (DU), 23; GU and DU, 7). The presence of cagDE was evaluated by polymerase chain reaction (PCR) and Southern hybridization. The vacA genotype was examined by PCR, using type-specific primers.

RESULTS

cagDE was present in 13 (86.7%) of 15 patients with GA, 26 (92.9%) of 28 patients with GU, 21 (91.3%) of 23 patients with DU, and 6 (85.7%) of 7 patients with GU and DU (P = 0.89). vacA signal sequence type s1 was found in 14 (93.3%) of 15 patients with GA, 26 (92.9%) of 28 patients with GU, 22 (95.7%) of 23 patients with DU, and 6 (85.7%) of 7 patients with GU and DU (P = 0.84). Sequences of cagDE and vacA in our Japanese strains were highly homologous with one another, and there were no disease-specific mutations.

CONCLUSIONS

Most of the H. pylori strains in Japan were cagDE-positive, vacA s1 type, regardless of clinical outcome. The present study also indicated that these genes were conserved well among our H. pylori isolates.

The site-specific integration of genetic elements may modulate thermostable protease production, a virulence factor in Dichelobacter nodosus, the causative agent of ovine footrot

The gram-negative anaerobe Dichelobacter nodosus is the causative agent of footrot in sheep. The authors have previously characterized two genetic elements, the intA (vap) and intB elements, which integrate into the genome of D. nodosus. In the virulent strain A198 there are two copies of the intA element. One copy is integrated into the 3' end of the tRNA-serGCU gene, close to the aspartokinase (askA) gene, and the second copy is integrated into the 3' end of the tRNA-serGGA gene, next to the polynucleotide phosphorylase (pnpA) gene. In this study, a new genetic element was identified in the benign strain C305, the intC element, integrated into the 3' end of the tRNA-serGCU gene, next to askA. The intC element was found in most D. nodosus strains, both benign and virulent, which were examined, and was integrated into tRNA-serGCU in most strains. Between the askA and tRNA-serGCU genes, a gene (designated glpA), was identified whose predicted protein product has very high amino acid identity with RsmA from the plant pathogen Erwinia carotovora. RsmA acts as a global repressor of pathogenicity in E. carotovora, by repressing the production of extracellular enzymes. In virulent strains of D. nodosus the intA element was found to be integrated next to pnpA, and either the intA or intC element was integrated next to glpA. By contrast, all but one of the benign strains had intB at one or both of these two positions, and the one exception had neither intA, intB nor intC at one position. The loss of the intC element from the virulent strain 1311 resulted in loss of thermostable protease activity, a virulence factor in D. nodosus. A model for virulence is proposed whereby integration of the intA and intC genetic elements modulates virulence by altering the expression of glpA, pnpA, tRNA-serGCU and tRNA-serGGA.

Gastric ulcers in SCID mice induced by Helicobacter pylori infection after transplanting lymphocytes from patients with gastric lymphoma

BACKGROUND & AIMS

Several studies have indicated that host factors are important in Helicobacter pylori-induced gastroduodenal diseases. We examined the pathological role of host immune responses in H. pylori infection by reconstituting components of the human immune system into severe combined immunodeficient (SCID) mice by transplantation of peripheral blood mononuclear cells (PBMCs) from H. pylori-infected patients.

METHODS

PBMCs obtained from patients with mucosa-associated lymphoid tissue (MALT) lymphoma were injected intraperitoneally into SCID mice, designated MALToma-hu-SCID mice. One month after transplantation, H. pylori was administered orally to the mice. The mice were killed and examined for pathological changes and immunologic features.

RESULTS

Human lymphocytes were detected in hu-SCID mice, and T- and B-cell functions were preserved for 1 month. Administration of H. pylori led to gastric ulcers with bleeding in the MALToma-hu-SCID mice. The gastric mucosa of control mice injected with Escherichia coli or transplanted with PBMCs from patients with peptic ulcers or gastritis or from healthy volunteers showed no pathological changes.

CONCLUSIONS

Host immune responses against H. pylori appear to be involved in the development of gastric ulcers in patients who have MALT lymphoma.

Studies of codon usage and tRNA genes of 18 unicellular organisms and quantification of Bacillus subtilis tRNAs: gene expression level and species-specific diversity of codon usage based on multivariate analysis

We examined codon usage in Bacillus subtilis genes by multivariate analysis, quantified its cellular levels of individual tRNAs, and found a clear constraint of tRNA contents on synonymous codon choice. Individual tRNA levels were proportional to the copy number of the respective tRNA genes. This indicates that the tRNA gene copy number is an important factor to determine in cellular tRNA levels, which is common with Escherichia coli and yeast Saccharomyces cerevisiae. Codon usage in 18 unicellular organisms whose genomes have been sequenced completely was analyzed and compared with the composition of tRNA genes. The 18 organisms are as follows: yeast S. cerevisiae, Aquifex aeolicus, Archaeoglobus fulgidus, B. subtilis, Borrelia burgdorferi, Chlamydia trachomatis, E. coli, Haemophilus influenzae, Helicobacterpylori, Methanococcusjannaschii, Methanobacterium thermoautotrophicum, Mycobacterium tuberculosis, Mycoplasma genitalium, Mycoplasma pneumoniae, Pyrococcus horikoshii, Rickettsia prowazekii, Synechocystis sp., and Treponema pallidum. Codons preferred in highly expressed genes were related to the codons optimal for the translation process, which were predicted by the composition of isoaccepting tRNA genes. Genes with specific codon usage are discussed in connection with their evolutionary origins and functions. The origin and terminus of replication could be predicted on the basis of codon usage when the usage was analyzed relative to the transcription direction of individual genes.

CagA and VacA: virulence factors of Helicobacter pylori in Thai patients with gastroduodenal diseases

BACKGROUND

The aim of this study was to assess the seroprevalence of cytotoxin-associated gene A (cagA) and vacuolating cytotoxin gene A (vacA) of Helicobacter pylori in selected Thai populations with specific gastroduodenal diseases.

MATERIALS AND METHODS

The immunoblot assay was used to detect serum antibodies against CagA and VacA obtained from the following patients: 87 cases of nonulcer dyspepsia (NUD), 61 cases of duodenal ulcer (DU), 49 cases of gastric ulcer (GU), and 10 cases of gastric cancer (GC).

RESULTS

Serum antibodies to CagA were detected in 75.4% of all patients (70. 1% of NUD, 78.7% of DU, 77.6% of GU, and 90% of GC). Although the prevalence of CagA seropositivity in GC patients was higher than in the other three groups, the difference was not statistically significant (p >.05).

CONCLUSIONS

The high seroprevalence of the CagA-positive H. pylori strain in patients with peptic ulcer, GC, and NUD indicates that this strain is common in Thai patients with gastroduodenal diseases. Furthermore, phenotypic classification of H. pylori into type 1 (CagA-positive, VacA-positive) and type 2 (CagA-negative, VacA-negative) is not a useful marker for screening patients with severe forms of gastroduodenal diseases.

A homologue of the Agrobacterium tumefaciens VirB and Bordetella pertussis Ptl type IV secretion systems is essential for intracellular survival of Brucella suis

Analysis of a TnblaM mutant of Brucella suis 1330, identified as being unable to multiply in Hela cells, allowed us to identify a 11 860 bp region of the B. suis genome encoding a type IV secretion system, homologous to the VirB system of Agrobacterium tumefaciens and the Ptl system of Bordetella pertussis. DNA sequence revealed 12 open reading frames (ORFs) encoding homologues of the 11 VirB proteins present in the pTi plasmid of Agrobacterium with a similar genetic organization, and a twelfth ORF encoding a putative lipoprotein, homologous to a protein involved in mating pair formation during bacterial conjugation and to adhesins used by Pseudomonas species to bind to plant roots. Phylogenetic trees based on the sequences of VirB4 and VirB9 protein homologues suggest that evolution of the systems from DNA transfer towards protein secretion did not stem from a single event but that the protein secretion systems have evolved independently. Four independent mutants in virB5, virB9 or virB10 were highly attenuated in an in vitro infection model with human macrophages. The virulence was restored by complementation with a plasmid containing the full virB region. The virB region appears to be essential for the intracellular survival and multiplication of B. suis.

A genetic basis for atrophy: dominant non-responsiveness and helicobacter induced gastritis in F(1) hybrid mice

BACKGROUND

The importance of host factors in helicobacter induced gastritis has been shown in animal models. Infection of most mouse strains with Helicobacter felis results in a functional atrophic gastritis, while other strains remain gastritis free.

AIMS

To investigate these host factors further by using genetic crosses of responder and non-responder mice.

METHODS

F(1) hybrids of the non-responder CBA/Ca strain and three strains of mice known to develop H felis induced gastritis were infected for three months with H felis. Gastritis was assessed by histopathology and serum antibody responses by ELISA.

RESULTS

Infection of CBA/Ca mice and F(1) hybrids induced little or no gastritis. Analyses of the antibody responses in these mice revealed virtually undetectable anti-helicobacter antibody levels despite colonisation with high numbers of H felis. In contrast, infection of H felis responsive strains induced gastritis and a significant humoral immune response.

CONCLUSIONS

The non-responsiveness of CBA/Ca mice to H felis infection is dominantly inherited. The lack of gastritis in CBA mice and their offspring is probably due to active suppression of the immune response normally mounted against H felis. Investigation of these mechanisms will provide important insights relevant to induction of gastric atrophy and cancer in humans.

Helicobacter pylori physiology predicted from genomic comparison of two strains

Helicobacter pylori is a gram-negative bacteria which colonizes the gastric mucosa of humans and is implicated in a wide range of gastroduodenal diseases. This paper reviews the physiology of this bacterium as predicted from the sequenced genomes of two unrelated strains and reconciles these predictions with the literature. In general, the predicted capabilities are in good agreement with reported experimental observations. H. pylori is limited in carbohydrate utilization and will use amino acids, for which it has transporter systems, as sources of carbon. Energy can be generated by fermentation, and the bacterium possesses components necessary for both aerobic and anaerobic respiration. Sulfur metabolism is limited, whereas nitrogen metabolism is extensive. There is active uptake of DNA via transformation and ample restriction-modification activities. The cell contains numerous outer membrane proteins, some of which are porins or involved in iron uptake. Some of these outer membrane proteins and the lipopolysaccharide may be regulated by a slipped-strand repair mechanism which probably results in phase variation and plays a role in colonization. In contrast to a commonly held belief that H. pylori is a very diverse species, few differences were predicted in the physiology of these two unrelated strains, indicating that host and environmental factors probably play a significant role in the outcome of H. pylori-related disease.

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.

Modulation of Helicobacter pylori induced interleukin-8 synthesis in gastric epithelial cells mediated by cag PAI encoded VirD4 homologue

BACKGROUND

Strains of Helicobacter pylori carrying the virulence associated cag pathogenicity island (PAI) induce gastric epithelial synthesis of the chemokine interleukin-8 (IL-8), a neutrophil chemoattractant, and thereby a strong inflammatory response during chronic infection of the human gastric mucosa. Previous mutational analyses have shown that many genes in the cag PAI are needed to elicit IL-8 synthesis in gastric epithelial cells, and also that some genes are not involved.

AIM

To test the possibility that certain genes in the cag PAI also downregulate (modulate) the inflammatory response elicited by cag+ H pylori infection.

METHODS

Cells of L5F11, a derivative of the Kato-3 gastric epithelial cell line that carries an engineered IL-8 promoter-luciferase reporter gene fusion, were cocultured with H pylori strain 26695 or with an isogenic mutant in which most of the cag PAI ORF 10 gene, an Agrobacterium virD4 homologue, was deleted. Luciferase activity was measured to assess IL-8 gene transcription and secreted IL-8 was measured by enzyme linked immunosorbent assay to assess synthesis and release of IL-8 protein from gastric epithelial cells.

RESULTS

Inactivation of ORF10 led to a 2.8-fold increase in IL-8 gene transcription and a 3.6-fold increase in IL-8 synthesis and secretion.

CONCLUSIONS

The results suggest that this VirD4 homologue participates in the control of inflammation that H pylori infection elicits by downregulating (modulating) the strong induction of IL-8 synthesis mediated by other cag encoded proteins.

HP0333, a member of the dprA family, is involved in natural transformation in Helicobacter pylori

Helicobacter pylori is naturally competent for DNA transformation, but the mechanism by which transformation occurs is not known. For Haemophilus influenzae, dprA is required for transformation by chromosomal but not plasmid DNA, and the complete genomic sequence of H. pylori 26695 revealed a dprA homolog (HP0333). Examination of genetic databases indicates that DprA homologs are present in a wide variety of bacterial species. To examine whether HP0333 has a function similar to dprA of H. influenzae, HP0333, present in each of 11 strains studied, was disrupted in two H. pylori isolates. For both mutants, the frequency of transformation by H. pylori chromosomal DNA was markedly reduced, but not eliminated, compared to their wild-type parental strains. Mutation of HP0333 also resulted in a marked decrease in transformation frequency by a shuttle plasmid (pHP1), which differs from the phenotype described in H. influenzae. Complementation of the mutant with HP0333 inserted in trans in the chromosomal ureAB locus completely restored the frequency of transformation to that of the wild-type strain. Thus, while dprA is required for high-frequency transformation, transformation also may occur independently of DprA. The presence of DprA homologs in bacteria known not to be naturally competent suggests a broad function in DNA processing.

Role of Helicobacter pylori cagA(+) strains and specific host immune responses on the development of premalignant and malignant lesions in the gastric cardia

The incidence rates of gastric cardia and esophageal adenocarcinomas are increasing, but data suggest that carriage of cagA(+) Helicobacter pylori strains may protect against development of Barrett's esophagus and esophageal adenocarcinoma. Our aims were to examine the relationship between pre-malignant and malignant lesions in the gastric cardia and serum antibodies to H. pylori antigens in patients with and without complications of Barrett's esophagus. The prevalence of carditis was 40% in controls compared with 13% in patients with complicated or uncomplicated Barrett's esophagus and cardia adenocarcinoma (p < 0.001). Cardia intestinal metaplasia (IM) and atrophy were present and concordant in 28% of controls but less frequent in patients with Barrett's alone or with dysplasia/adenocarcinoma (0% for each, p < 0.001). Carriage of cagA(+) strains was present in 34% of patients with carditis and significantly associated with increased frequency and severity of cardia inflammation, IM, and atrophy but not with adenocarcinoma. IgA and HspA seropositivity were significantly increased in H. pylori-colonized patients with carditis compared to persons with normal cardia histology (p </= 0.005) but not in persons with esophageal disease or cardia adenocarcinoma. We conclude that carriage of cagA(+) H. pylori strains and induction of particular serological responses are significantly associated with marked histological findings in the gastric cardia but not with adenocarcinoma of either the gastric cardia or esophagus.

Comparative analysis of Legionella pneumophila and Legionella micdadei virulence traits

While the majority of Legionnaire's disease has been attributed to Legionella pneumophila, Legionella micdadei can cause a similar infection in immunocompromised people. Consistent with its epidemiological profile, the growth of L. micdadei in cultured macrophages is less robust than that of L. pneumophila. To identify those features of the Legionella spp. which are correlated to efficient growth in macrophages, two approaches were taken. First, a phenotypic analysis compared four clinical isolates of L. micdadei to one well-characterized strain of L. pneumophila. Seven traits previously correlated with the virulence of L. pneumophila were evaluated: infection and replication in cultured macrophages, evasion of phagosome-lysosome fusion, contact-dependent cytotoxicity, sodium sensitivity, osmotic resistance, and conjugal DNA transfer. By nearly every measure, L. micdadei appeared less virulent than L. pneumophila. The surprising exception was L. micdadei 31B, which evaded lysosomes and replicated in macrophages as efficiently as L. pneumophila, despite lacking both contact-dependent cytopathicity and regulated sodium sensitivity. Second, in an attempt to identify virulence factors genetically, an L. pneumophila genomic library was screened for clones which conferred robust intracellular growth on L. micdadei. No such loci were isolated, consistent with the multiple phenotypic differences observed for the two species. Apparently, L. pneumophila and L. micdadei use distinct strategies to colonize alveolar macrophages, causing Legionnaire's disease.

Essential components of the Ti plasmid trb system, a type IV macromolecular transporter

The trb operon from pTiC58 is one of three loci that are required for conjugal transfer of this Ti plasmid. The operon, which probably codes for the mating bridge responsible for pair formation and DNA transfer, contains 12 genes, 11 of which are related to genes from other members of the type IV secretion system family. The 12th gene, traI, codes for production of Agrobacterium autoinducer (AAI). Insertion mutations were constructed in each of the 12 genes, contained on a full-length clone of the trb region, using antibiotic resistance cassettes or a newly constructed transposon. This transposon, called mini-Tn5Ptrb, was designed to express genes downstream of the insertion site from a promoter regulated by TraR and AAI. Each mutation could trans complement downstream Tn3HoHo1 insertions in the trb operon of full-sized Ti plasmids. When marker-exchanged into the transfer-constitutive Ti plasmid pTiC58DeltaaccR mutations in trbB, -C, -D, -E, -L, -F, -G, and -H abolished conjugal transfer from strain UIA5, which lacks the 450-kb catabolic plasmid pAtC58. However, these mutants retained residual conjugal transfer activity when tested in strain NT1, which contains this large plasmid. The trbJ mutant failed to transfer at a detectable frequency from either strain, while the trbI mutant transferred at very low but detectable levels from both donors. Only the trbK mutant was unaffected in conjugal transfer from either donor. Transfer of each of the marker-exchange mutants was restored by a clone expressing only the wild-type allele of the corresponding mutant trb gene. An insertion mutation in traI abolished the production of AAI and also conjugal transfer. This defect was restored by culturing the mutant donor in the presence of AAI. We conclude that all of the trb genes except trbI and trbK are essential for conjugal transfer of pTiC58. We also conclude that mutations in any one of the trb genes except traI and trbJ can be complemented by functions coded for by pAtC58.

Transfer RNAs and pathogenicity islands

The tRNAs are central components in translation. In addition, they are essential for replication of retroviruses: tRNAs bind to viral genomes through their 3'-end sequences and act as primers for initiation of viral replication. Here, I discuss the possibility that tRNAs also play a role in the horizontal transfer of bacterial pathogenicity islands between different pathogens. Such a role would implicate tRNAs in DNA recombination.

Anti-CagA reactivity in Helicobacter pylori-negative subjects: a comparison of three different methods

Emerging evidence suggests that infection by CagA-positive Helicobacter pylori strains is related to the development of more serious gastroduodenal diseases, thus conferring to the determination of anti-CagA antibodies a relevant clinical significance in serological screenings. The detection of anti-CagA positivity in sera negative for anti-H. pylori antibodies raises the question of whether this apparently nonsense result is merely due to a false positive reaction. To address this issue, we compared three different methods for the detection of anti-CagA antibodies. In all, 272 selected sera from patients with precisely defined H. pylori status (positive or negative concordance of five tests, ie, histology by Giemsa in both antrum and corpus, rapid urease test, culture, [13C]urea breath test, IgG ELISA) were tested for anti-CagA reactivity by three different techniques (western immunoblotting, ELISA, and recombinant immunoblotting assay). In order to assess the sensibility and specificity of each tests, we considered as "true" anti-CagA positive sera those with two out of three positive results. Sera from 70% of H. pylori-positive patients and 10% from H. pylori-negative patients turned out to be "true" positives for anti-CagA antibodies. The three methods showed similar excellent results, in terms of both sensitivity and specificity, always over 93%. It is confirmed that a proportion of patients with a negative conventional serology against H. pylori possess anti-CagA antibodies in their sera. In this paper we demonstrate that it can happen even in patients without any biological signs of actual H. pylori infection. The possibility that this can be due to a false positive laboratory result is very likely ruled out by the accuracy of the three methods used. The clinical management of these patients needs further study on larger series.

Exploring novel vaccines against Helicobacter pylori: protective and therapeutic immunization

Infection of human stomach by Helicobacter pylori, a gram negative spiral bacterium first isolated in 1983 from a patient with chronic active gastritis (1), causes nearly all duodenal ulcers and most gastric ulcers and is associated with an increased risk of gastric adenocarcinoma (2). Current therapies for gastric infections include combination triple or quadruple therapy of antimicrobial and/or antiulcer agents for eradication of H. pylori infection (3). Development of the resistant strains and ecological niche (habitant) of the bacteria may cause relapse after the termination of the therapy. However, if effective, the high cost, difficulty of patient compliance and risk of selection for resistant strains make these therapeutic regimens impractical on a large scale, though effective on the laboratory trial stages. Studies of the pathogenesis of H. pylori have led to the identification of bacterial antigens and adherin proteins as candidates for inclusion as novel vaccines against these diseases (4-7). Both prophylactic and therapeutic vaccination have been demonstrated in animal models of H. pylori infection (8-10).

Multiple genes in the left half of the cag pathogenicity island of Helicobacter pylori are required for tyrosine kinase-dependent transcription of interleukin-8 in gastric epithelial cells

Helicobacter pylori strains that contain the cag pathogenicity island (PAI) elicit increased synthesis of gastric C-X-C chemokines, promote neutrophilic infiltration into the gastric epithelium, and stimulate the synthesis of interleukin-8 (IL-8) in cultured gastric epithelial cells. To investigate the effects of cag PAI genes on the transcription of the IL-8 gene, the Kato-3 gastric epithelial cell line was stably transfected with plasmid DNA containing the IL-8 gene promoter fused to a luciferase reporter gene. The resulting reporter cell line, L5F11, was used to monitor the effects of infection in cell culture by H. pylori 26695 and isogenic derivatives with null mutations in genes in the cag PAI on transcription of the IL-8 gene. We found that null mutations in eight open reading frames, including homologs of the Agrobacterium virB9, virB10, and virB11 genes, in the left half of the cag PAI abrogated the induction of IL-8 gene transcription. Further studies with the L5F11 cell line showed that IL-8 gene transcription induced by H. pylori was blocked by the protein tyrosine kinase inhibitor herbimycin A but not by the protein kinase C inhibitor calphostin C or by the protein kinase G inhibitor KT5823. IL-8 gene transcription in L5F11 cells could also be induced by the cytokine tumor necrosis factor alpha (TNF-alpha) without exposure to H. pylori. This TNF-alpha-induced IL-8 transcription was inhibited by the protein kinase A inhibitor H7, which had no significant effect on H. pylori-induced IL-8 transcription. These studies show that multiple genes in the left half of the cag PAI are essential for the transcription of the IL-8 gene in gastric epithelial cells and that this depends on protein tyrosine kinase activation.

Relationship between the cagA 3' repeat region of Helicobacter pylori, gastric histology, and susceptibility to low pH

BACKGROUND & AIMS

The variation in size of Helicobacter pylori CagA is related to repeat sequences in the 3' region of the cagA gene. We investigated whether structural subtypes of the cagA 3' region are associated with presentation of the infection or to susceptibility to acid.

METHODS

We examined 319 cagA-positive H. pylori isolates: 84 isolates from Bogota, Colombia; 83 from Houston, Texas; 24 from Siena, Italy; and 128 from Seoul, Korea. The cagA 3' region was amplified by polymerase chain reaction. Gastric histology and susceptibility to pH 3 were evaluated in relation to the number of cagA repeat regions.

RESULTS

Strains with more than three repeat regions were associated with significantly higher scores for gastric mucosal atrophy and intestinal metaplasia than those with fewer repeat regions. H. pylori strains with three repeat regions were also significantly more susceptible to pH 3 than isolates with fewer repeat regions.

CONCLUSIONS

H. pylori strains with more than three repeat regions in the 3' region of the cagA gene are associated with enhanced histological injury and with reduced survival in acidic conditions. It is hypothesized that these variants arise within the stomach.

VacA genotyping directly from gastric biopsy specimens and estimation of mixed Helicobacter pylori infections in patients with duodenal ulcer and gastritis

BACKGROUND

The vacA genotypes and the cagA gene status were investigated in 80 Helicobacter pylori-infected patients with duodenal ulcer (DU) and 49 with gastritis only.

METHODS

Lysates of gastric biopsy specimens were used directly for polymerase chain reaction-based detection.

RESULTS

The ml subtype was found in 36% and 31% and the m2 in 36% and 46% of specimens from patients with DU and gastritis, respectively (P > 0.05). In 15% of samples the midregion remained unclassified. The prevalence rate of s1 subtypes was higher in cases of DU (69%) than in gastritis (43%) (P < 0.0001); the opposite correlation was observed for s2. The cagA gene was detected in 80% of patients with DU and in 52% of those with gastritis (P < 0.0001). Infections with multiple H. pylori strains exceeded 50% in both groups.

CONCLUSIONS

These results suggest that vacA s1 genotype and cagA+ status are associated with higher DU prevalence and that mixed H. pylori infections are very common in our geographic region.

Characterization of IS1541-like elements in Yersinia enterocolitica and Yersinia pseudotuberculosis

We characterized Yersinia enterocolitica and Yersinia pseudotuberculosis insertion sequences related to insertion sequence 1541, recently identified in Yersinia pestis. For each of the two species, two insertion sequence copies were cloned and sequenced. Genetic elements from Y. pseudotuberculosis were almost identical to insertion sequence 1541, whereas these from Y. enterocolitica were less related. Phylogenetic analysis of the putative transposases encoded by insertion sequences from the three pathogenic members of the genus Yersinia showed that they clustered with those encoded by Escherichia coli and Salmonella enterica elements belonging to the insertion sequence 200/insertion sequence 605 group. Insertion sequences originating from Y. pestis and Y. pseudotuberculosis constitute a monophyletic lineage distinct from that of Y. enterocolitica.

Distinct variants of Helicobacter pylori cagA are associated with vacA subtypes

The diversity of the cytotoxin-associated gene (cagA) of Helicobacter pylori was analyzed in 45 isolates obtained from nine countries. We examined variation in the 5' end of the cagA open reading frame as determined by PCR and sequencing. Phylogenetic analysis revealed the existence of at least two distinct types of cagA. One variant (cagA1) was found exclusively in strains from Europe, the United States, and Australia, whereas a novel variant (cagA2) was found in strains from East Asia. The greatest diversity between cagA1 and cagA2 was found in the first 20 amino acids of the cagA open reading frame, where several consistent insertions or deletions were observed. Additional cagA sequence variants that could be classified as separate subtypes were found in two of three Peruvian and in five of seven U.S. strains tested. The calculated isoelectric point of the first 154 amino acids of the cagA1 variants (7.52 +/- 1.54) was significantly higher than that of the first 154 amino acids of the cagA2 variants (5.61 +/- 0.94; P < 0.001). Most cagA2 strains contained vacA subtype s1c (P < 0.001), and in vacA m1 strains cagA1 was more frequently observed than cagA2. These results show the epidemiological relationship between cagA and vacA at the subtype level and indicate the existence of distinct H. pylori lineages that are not uniformly distributed over the globe.

The selC-associated SHI-2 pathogenicity island of Shigella flexneri

Pathogenicity islands are chromosomal gene clusters, often located adjacent to tRNA genes, that encode virulence factors present in pathogenic organisms but absent or sporadically found in related non-pathogenic species. The selC tRNA locus is the site of integration of different pathogenicity islands in uropathogenic Escherichia coli, enterohaemorrhagic E. coli and Salmonella enterica. We show here that the selC locus of Shigella flexneri, the aetiological agent of bacterial dysentery, also contains a pathogenicity island. This pathogenicity island, designated SHI-2 (Shigella island 2), occupies 23.8 kb downstream of selC and contains genes encoding the aerobactin iron acquisition siderophore system, colicin V immunity and several novel proteins. Remnants of multiple mobile genetic elements are present in SHI-2. SHI-2-hybridizing sequences were detected in all S. flexneri strains tested and parts of the island were also found in other Shigella species. SHI-2 may allow Shigella survival in stressful environments, such as those encountered during infection.

Relationship between Helicobacter pylori iceA, cagA, and vacA status and clinical outcome: studies in four different countries

There is continuing interest in identifying Helicobacter pylori virulence factors that might predict the risk for symptomatic clinical outcomes. It has been proposed that iceA and cagA genes are such markers and can identify patients with peptic ulcers. We compared H. pylori isolates from four countries, looking at the cagA and vacA genotypes, iceA alleles, and presentation of the infection. We used PCR to examine iceA, vacA, and cagA status of 424 H. pylori isolates obtained from patients with different clinical presentations (peptic ulcer, gastric cancer, and atrophic gastritis). The H. pylori isolates examined included 107 strains from Bogota, Colombia, 70 from Houston, Tex., 135 from Seoul, Korea, and 112 from Kyoto, Japan. The predominant genotype differed among countries: the cagA-positive iceA1 vacA s1c-m1 genotype was predominant in Japan and Korea, the cagA-positive iceA2 vacA s1b-m1 genotype was predominant in the United States, and the cagA-positive iceA2 vacA s1a-m1 genotype was predominant in Colombia. There was no association between the iceA, vacA, or cagA status and clinical outcome in patients in the countries studied. iceA status shows considerable geographic differences, and neither iceA nor combinations of iceA, vacA, and cagA were helpful in predicting the clinical presentation of an H. pylori infection.

Serum antibody responses to Helicobacter pylori and the cagA marker in patients with mucosa-associated lymphoid tissue lymphoma

The lymphoma of the mucosa-associated lymphoid tissue (MALT) of the stomach has been linked to Helicobacter pylori infection, but the mechanisms involved in B-cell proliferation remain elusive. In a search for putative H. pylori-specific monoclonal immunoglobulin production, an H. pylori strain was isolated from 10 patients with MALT lymphoma and used to detect the specific serum antibody response to the homologous strain by immunoblotting. Moreover, the antigenicity of the different strains was compared by using each of the 10 sera. We found that the different strains induced highly variable patterns of systemic immunoglobulin G antibody response, although several bacterial antigens, such as the 60-kDa urease B, were often recognized by the different sera. The cagA marker was detected in the strains by PCR with specific primers and by dot blot analysis, and the CagA protein was found in the sera of 4 of the 10 patients by immunoblotting. In conclusion, MALT lymphoma patients, like other patients with H. pylori gastritis, exhibit a polymorphic systemic antibody response, despite an apparently similar antigenic profile. The CagA marker of pathogenicity is not associated with this disease.

Analysis of vacA, cagA, and IS605 genotypes and those determined by PCR amplification of DNA between repetitive sequences of Helicobacter pylori strains isolated from patients with nonulcer dyspepsia or mucosa-associated lymphoid tissue lymphoma

The vacA s and m genotypes and the presence of cagA and IS605 were determined in Helicobacter pylori strains from patients with mono- and multiple infections. Surprisingly, these genetic markers were not associated with nonulcer dyspepsia or mucosa-associated lymphoid tissue lymphoma. The presence of cagA correlated with the presence of the vacA s1 allele (P < 0.05), whereas the presence of IS605 was associated with the presence of the s2 allele (P < 0.05).

Effect of an aluminum hydroxide-magnesium hydroxide combination drug on adhesion, IL-8 inducibility, and expression of HSP60 by Helicobacter pylori

BACKGROUND

Co-magaldrox (Maalox) is used world-wide as an antacid and as a cytoprotective agent for gastritis and peptic ulcer diseases. We examined the effects of co-magaldrox on Helicobacter pylori.

METHODS

Adhesion of H. pylori to human gastric epithelial cells (MKN45) was evaluated by flow cytometry. Morphologic changes in H. pylori caused by co-magaldrox were determined by scanning electron microscopy. Induction of interleukin-8 (IL-8) from MKN45 cells was examined with enzyme-linked immunosorbent assay, and the intracellular and extracellular expression of heat-shock protein 60 (HSP60) was analyzed with sodium dodecyl sulphate-polyacrylamide gel electrophoresis and flow cytometry.

RESULTS

Adhesion of H. pylori to MKN 45 cells was significantly inhibited by 1.25%-5% comagaldrox. H. pylori aggregated with co-magaldrox according to an electron microscopic examination. IL-8 secretion from MKN45 cells after H. pylori infection was also inhibited by co-magaldrox. Extracellular expression of HSP60 on the surface of H. pylori was decreased after treatment with comagaldrox, whereas the intracellular synthesis of HSP60 was not. HSP60-induced IL-8 secretion was significantly inhibited by co-magaldrox in a dose-dependent manner.

CONCLUSIONS

These results show that co-magaldrox suppressed the expression of the following virulence factors: adhesion, IL-8 inducibility, and expression of extracellular HSP60. Therefore, co-magaldrox is a potent anti-H. pylori and cytoprotective drug.

Sequence anomalies in the Cag7 gene of the Helicobacter pylori pathogenicity island

The severity of Helicobacter pylori-related disease is correlated with a pathogenicity island (the Cag region of about 26 genes) whose presence is associated with the up-regulation of an IL-8 cytokine inflammatory response in gastric epithelial cells. Statistical analysis of the Cag gene sequences calculated from the complete genome of strain 26695 revealed several unusual features. The Cag7 sequence (1,927 aa) has two repeat regions. Repeat region I runs 317 aa in a form of AAA proximal to the protein N terminal; repeat region II extends 907 aa in the middle of the protein sequence consisting of 74 contiguous segments composed from selections among six consensus sequences and includes 58 regularly distributed cysteine residues with consecutive cysteines mostly 12, 18, or 24 aa apart. This "regular" cysteine arrangement may provide a scaffolding of linker elements stabilized by disulfide bridges. When Cag7 homologues from different strains are compared, differences were found almost exclusively in the repeat regions, resulting from deletion and/or insertion of repeating units. These observations suggest that the anomalous repetitive structure of the sequence plays an important role in the conformation of Cag7 gene product and potentially in the function of the pathogenicity island. Other facets of the Cag7 sequence show significant charge clusters, high multiplet count, and extremes of amino acid usage.

Molecular and cellular activities of Helicobacter pylori pathogenic factors

Stomach infection with pathogenic strains of Helicobacter pylori causes in some patients severe gastroduodenal diseases. These bacteria produce various virulence factors and, here, we review the recent acquisition on the biochemical mode of action of three major factors. We discuss the role of urease both as buffer of the stomach pH and as source of ammonia. The vacuolating toxin alters the endocytic pathway of non-polarized cells, inducing the release of acid hydrolases, the depression of extracellular ligand degradation and of antigen processing and, in the presence of ammonia, swelling of late-prelysosomal compartments. In polarized epithelial monolayers, vacuolating toxin induces an increase of the paracellular permeability, independent of vacuolation. The neutrophil activating protein induces the production of oxygen radicals in human neutrophils and could contribute to the damage of the stomach mucosa. The activities of these factors are discussed in terms of the need of the bacterium of increasing the supply of nutrients from the stomach lumen and from the mucosa.

Release of Helicobacter pylori vacuolating cytotoxin by both a specific secretion pathway and budding of outer membrane vesicles. Uptake of released toxin and vesicles by gastric epithelium

The mechanisms by which Helicobacter pylori releases its virulence factors are poorly known. Active secretion has been proposed for some products, including a vacuolating toxin (VacA). Outer membrane vesicles represent another mechanism by which some Gram-negative bacteria may release virulence factors. This study sought to localize VacA by immunocytochemistry in H. pylori cells, to determine whether H. pylori produces outer membrane vesicles, and to investigate whether such vesicles might constitute a vehicle for the delivery of bacterial virulence factors to the gastric mucosa. Small (50-300 nm) membrane vesicles were found in H. pylori culture media from both H. pylori strain 60190 and strain CCUG 17874. These vesicles appeared to originate from blebs arising on the bacterial outer membrane. VacA was immunolocalized in the periplasm and outer membrane of intact bacteria and also in outer membrane blebs and vesicles. Both soluble secreted VacA and VacA-containing vesicles bound to, and were internalized by, MKN28 cells and were detectable in the gastric mucosa from H. pylori-infected humans. The release of outer membrane vesicles by H. pylori may represent a mechanism, additional to secretory pathways, for the delivery of bacterial toxins and antigens to the gastric mucosa.

Effect of Helicobacter pylori infection and its eradication on cell proliferation, DNA status, and oncogene expression in patients with chronic gastritis

BACKGROUND

Helicobacter pylori, the main cause of chronic gastritis, is a class I gastric carcinogen. Chronic gastritis progresses to cancer through atrophy, metaplasia, and dysplasia. Precancerous phenotypic expression is generally associated with acquired genomic instability.

AIM

To evaluate the effect of H pylori infection and its eradication on gastric histology, cell proliferation, DNA status, and oncogene expression.

METHODS/SUBJECTS

Morphometric and immunohistochemical techniques were used to examine gastric mucosal biopsy specimens from eight controls, 10 patients with H pylori negative chronic gastritis, 53 with H pylori positive chronic gastritis, and 11 with gastric cancer.

RESULTS

All patients with chronic gastritis were in a hyperproliferative state related to mucosal inflammation, regardless of H pylori infection. Atrophy was present in three of 10 patients with H pylori negative chronic gastritis and in 26 of 53 with H pylori positive chronic gastritis, associated in 18 with intestinal metaplasia. DNA content was abnormal in only 11 patients with atrophy and H pylori infection; eight of these also had c-Myc expression, associated in six cases with p53 expression. Fifty three patients with H pylori positive chronic gastritis were monitored for 12 months after antibiotic treatment: three dropped out; infection was eradicated in 45, in whom cell proliferation decreased in parallel with the reduction in gastritis activity; atrophy previously detected in 21/45 disappeared in five, regressed from moderate to mild in nine, and remained unchanged in seven; complete metaplasia disappeared in 4/14, and markers of genomic instability disappeared where previously present. In the five patients in whom H pylori persisted, atrophy, metaplasia, dysplasia, and markers of genomic instability remained unchanged.

CONCLUSIONS

Chronic H pylori infection seems to be responsible for genomic instability in a subset of cases of H pylori positive chronic atrophic gastritis; eradication of H pylori infection can reverse inflammation and the related atrophy, metaplasia, and genomic instability.

A conventional beagle dog model for acute and chronic infection with Helicobacter pylori

Helicobacter pylori has been widely recognized as an important human pathogen responsible for chronic gastritis, peptic ulcers, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma. Little is known about the natural history of this infection since patients are usually recognized as having the infection only after years or decades of chronic disease. Several animal models of H. pylori infection, including those with different species of rodents, nonhuman primates, and germ-free animals, have been developed. Here we describe a new animal model in which the clinical, pathological, microbiological, and immunological aspects of human acute and chronic infection are mimicked and which allows us to monitor these aspects of infection within the same individuals. Conventional Beagle dogs were infected orally with a mouse-adapted strain of H. pylori and monitored for up to 24 weeks. Acute infection caused vomiting and diarrhea. The acute phase was followed by polymorphonuclear cell infiltration, interleukin 8 induction, mononuclear cell recruitment, and the appearance of a specific antibody response against H. pylori. The chronic phase was characterized by gastritis, epithelial alterations, superficial erosions, and the appearance of the typical macroscopic follicles that in humans are considered possible precursors of MALT lymphoma. In conclusion, infection in this model mimics closely human infection and allows us to study those phases that cannot be studied in humans. This new model can be a unique tool for learning more about the disease and for developing strategies for treatment and prevention.

Direct determination of Helicobacter pylori vacA genotypes and cagA gene in gastric biopsies and relationship to gastrointestinal diseases

OBJECTIVE

Our aim was to detect Helicobacter pylori (H. pylori) from gastric biopsies of 248 patients using a novel, polymerase chain reaction (PCR)-based methodology, which simultaneously facilitates the determination of H. pylori vacA genotypes and cagA gene.

METHODS

A simple methodology for sample preparation was established and PCR was performed with primer systems for the 16S rRNA, vacA, and cagA genes, thus circumventing the need to culture H. pylori and to extract DNA from biopsy samples.

RESULTS

Infection with H. pylori was detected in 147 (59.3%) of 248 patients. The vacA signal sequence genotype s1 was present in 104 (81.3%) of 128 H. pylori-positive patients, and 24 (18.8%) patients had the genotype s2. The vacA middle region types m1 and m2 were detected in 46 (35.9%) and 79 (61.7%) patients, respectively. The combinations s1/m2 (43%) and s1/m1 (35.9%) were found more frequently than s2/m2 (18.8%). The cagA gene was detected in 75 (72.1%) of 104 H. pylori-positive biopsies with the vacA genotype s1. All 24 biopsies with the type s2 were cagA negative. Strains of the type vacA s1 were found in 97% of H. pylori-positive patients with peptic ulcer disease and were associated with the presence of the cagA gene, whereas 96% of the strains of the type vacA s2 were detected in patients who only had nonulcer dyspepsia.

CONCLUSIONS

Using a novel PCR-based methodology, H. pylori 16S rRNA gene, vacA genotypes, and cagA gene can now be rapidly detected directly in gastric biopsies with high accuracy. These data demonstrate that infection with H. pylori strains of the vacA s1 genotype and the cagA gene are more likely to result in peptic ulcer disease. Determination of vacA genotypes and cagA gene may contribute to the potential clinical identification of patients at different levels of risk.

Rapid genomic diversification of Helicobacter pylori

Helicobacter pylori was cultured from antrum and corpus gastric biopsies from 65 patients originating from two separate groups: (i) a geographically linked group and (ii) a geographically nonlinked group. Genomic DNA was recovered from the clinical isolates and subjected to restriction fragment length polymorphism (RFLP) analysis after digestion with DraI. Southern blots were probed with the oligonucleotide (GTG)5, the riboprobe pKK3535, and the cagA gene probe pMC3. (GTG)5 and cagA DNA fingerprints and ribopatterns suggested that most of the patients were infected with their own unique strain; however, some were infected with multiple strains. Minor genomic differences were detected in many antrum/corpus sample pairs (clonal variants), suggesting rapid evolutionary change in domains detected by (GTG)5. The high degree of genomic diversity detected by (GTG)5 may reflect structural versatility of these domains. The genomic diversity indicates that infection by H. pylori in a defined community does not appear to be limited to certain RFLP types.

Helicobacter pylori-associated gastritis in mice is host and strain specific

The vacA and cagA geno- and phenotypes of two mouse-adapted strains of Helicobacter pylori, SS1 and SPM326, were determined. The SS1 strain, which had the cagA+ and vacA s2-m2 genotype, induced neither vacuole formation in HeLa cells nor interleukin-8 (IL-8) production in KATO III cells. In contrast, H. pylori SPM326, with the cagA+ and vacA s1b-m1 genotype, induced vacuoles as well as IL-8 production in vitro. Furthermore, a spontaneous mutant of SPM326, which produced a vacuolating cytotoxin but was not able to induce IL-8 production (SPM326/IL-8(-)), was detected. C57Bl/6 and BALB/c mice were infected with these three strains to investigate the colonization pattern and the effect on the immune response in vivo. The SS1 strain colonized the stomachs of all mice in large numbers which remained constant over time. Colonization with the SPM326/IL-8(+) and SPM326/IL-8(-) strains was lesser, or even absent, and decreased over time. At 5 weeks postinoculation all three H. pylori strains induced a mild increase of neutrophil count in the gastric corpus of C57Bl/6 mice, which disappeared by 12 weeks. At both 5 and 12 weeks postinoculation C57Bl/6 mice colonized with SPM326/IL-8(+) showed an increased expression of major histocompatibility complex (MHC) class II antigen in the cardia which was accompanied by an increased number of T cells. C57Bl/6 mice that were infected with SS1 and SPM326/IL-8(-) did not show chronic inflammation. BALB/c mice colonized with SS1 and SPM326/IL-8(-) also showed an increase in neutrophil count at 5 weeks, which normalized again by 12 weeks postinoculation. At this time point SS1-infected mice showed inflammation in the corpus and antrum. At these sites an increased expression of MHC class II antigens and an increased number of T cells were observed. Although small lymphoid follicles were already observed 5 weeks after inoculation with SS1, their incidence as well as their number was increased at 12 weeks. These results show that inflammation induced by H. pylori depends both on the bacterial strain and the host.

Effects of Helicobacter pylori on proliferation of gastric epithelial cells in vitro

OBJECTIVE

H. pylori infection of the gastric mucosa has been associated with an increase in gastric epithelial cell proliferation. However, in vitro adherence of H. pylori to gastric epithelial cells is associated with reduced cell proliferation. Reduction of epithelial cell proliferation may contribute to ulcer formation and delay ulcer healing. The following study was undertaken to elucidate the ability of cagA-positive and -negative strains to impede gastric epithelial cell proliferation.

METHODS

A human gastric adenocarcinoma cell line (AGS) was overlaid with either cagA-positive or cagA-negative H. pylori strains suspended in cell culture medium. Proliferation of AGS cells was analyzed by performing direct cell counts and by measuring metabolism of a soluble tetrazolium compound (MTS), after exposure to H. pylori for 24 h.

RESULTS

When compared with control cells cultured in medium alone, AGS cell proliferation was reduced by 45.6% and 28.5% due to exposure to cagA-negative and cagA-positive strains, respectively. When bacterial-induced cytotoxicity was assessed by measuring release of lactose dehydrogenase (LDH) into the culture medium, cagA-positive strains were shown to induce significantly more cytotoxicity than cagA-negative strains.

CONCLUSIONS

These experiments demonstrate that H. pylori exposure to AGS cells significantly reduces cell proliferation. However, cagA-positive strains that induce more cell injury reduce cell proliferation to a lesser extent than cagA-negative strains. Persistent replication of gastric epithelial cells injured by exposure to cagA-positive strains may be partially responsible for the stronger association with gastric cancer in persons infected with cagA-positive H. pylori strains.

Genotypes of Helicobacter pylori obtained from gastric ulcer patients taking or not taking NSAIDs

OBJECTIVE

Whether Helicobacter pylori infection and use of nonsteroidal antiinflammatory drugs (NSAIDs) are independent risk factors for ulcerogenesis remains unclear. We undertook this study to evaluate H. pylori isolates from gastric ulcer patients to determine whether the genotype of the infecting isolate could be correlated with the use or nonuse of NSAIDs.

METHODS

Fifty-two patients presenting with gastric ulcer and infected with H. pylori were included; 26 patients were taking NSAIDs or aspirin (ASA) regularly at the time of ulcer diagnosis. Polymerase chain reaction (PCR) was employed to assess the presence and mosaicism of the following H. pylori genes: cagA, vacA, iceA, and picB.

RESULTS

We found no statistical differences in the presence of these genes in H. pylori isolates from gastric ulcer patients taking or not taking prescription NSAIDs or ASA. A 297-bp fragment of the cagA gene was detected in 96% of the isolates from the NSAID and ASA users and 100% from the non-NSAID users (p = 1.0). A larger and more variable region of the cagA gene was detected more frequently among the isolates from non-NSAID users than those from NSAID users (p = 0.05). Ninety-two percent of the isolates were identified as vacA genotype s1. The dominant vacA subtype was s1b, 76.9% and 65.4% in isolates from non-NSAID-taking or NSAID-taking patients, respectively (p = 0.4). iceA1 genotype was not correlated with gastric ulcer as this allele was only detected in 17.3% of all isolates.

CONCLUSIONS

No significant differences in the presence of the candidate virulence genes vacA, cagA, picB, or iceA were detected in isolates from gastric ulcer patients taking prescription NSAIDs or ASA, compared with those not taking these drugs, indicating that single gene presence does not allow discrimination of isolates that may be important in NSAID-induced ulcerogenesis. A variable region of the cagA gene was more frequently detected in isolates from patients not taking NSAIDs or ASA, suggesting that this gene may be modified by NSAID- or ASA-related factors or that certain strains may be selected for in patients taking these medications.

cagA gene and vacA alleles in Spanish Helicobacter pylori clinical isolates from patients of different ages

The prevalence of the cagA gene and vacA alleles in 124 Spanish Helicobacter pylori clinical isolates from patients of different ages ranging from 3 to 78 years was studied (21 patients < or = 10 years, 30 patients 11-20 years, 17 patients 21-40 years, 31 patients 41-60 years and 25 patients 61-80 years). The cagA gene and vacA s1 or vacA s2 alleles were identified by PCR from the strain. 66.9% of the isolates were cagA+ and 33.1% cagA-. vacA s1 was detected in 48.4% of the isolates and vacA s2 in 51.6%. 44.4% of patients were cagA+/vacA s1, 22.5% were cagA+/vacA s2, 4% were cagA-/vacA s1 and 29% were cagA-/vacA s2. The percentage of cagA+ isolates and the vacA s1 alleles in the different groups were as follows: 23.8% and 28.6% in 0-10 years, 40% and 30% in 11-20 years, 88.2% and 70.6% in 21-40 years, 90.3% and 70.9% in 41-60 years and 92% and 44% in the 61-78 years group. 93% (54/58) of isolates found in ulcer patients and 90.9% (10/11) of isolates from gastritis patients older than 20 years were cagA+. In patients younger than 20 years ulcer disease was rare with 60% of isolates being cagA+ (3/5) compared with 31.6% cagA+ isolates (12/38) in patients suffering from gastritis in the younger group. The prevalence of the cagA gene and vacA s1 allele increased with age, being more frequent in older patients than in younger.

Relation between vacA subtypes, cytotoxin activity, and disease in Helicobacter pylori-infected patients from The Netherlands

OBJECTIVE

The vacuolating cytotoxin of Helicobacter pylori (H. pylori) is encoded by vacA, of which allelic variation has been described. In the U.S., H. pylori strains with the signal sequence allele s1a are associated with enhanced gastric inflammation and with peptic ulcer disease (PUD). The m1 middle region allele is linked with more severe gastric epithelial damage. However, the distribution of H. pylori genotypes and the association with disease may be different in other geographical areas. The aim of this study was to establish whether vacA types among H. pylori isolates from Dutch patients are associated with disease.

METHODS

The cytotoxin activity of the H. pylori isolates from 34 PUD patients and 46 patients with functional dyspepsia (FD) was assessed by an in vitro assay using HeLa cells as indicator cells. The vacA types and cagA status of the isolates were assessed by polymerase chain reaction (PCR).

RESULTS

vacA s1-type H. pylori displayed cytotoxin activity more frequently than s2 vacA-type H. pylori (p = 0.003). This difference was not significant when only cagA+ H. pylori were considered. H. pylori isolates with the m1 vacA type exhibited a higher cytotoxin activity, independent of cagA (p = 0.006). Ninety-four percent (32/34) of the PUD patients and 74% (34/46) of the FD patients were infected with s1 vacA-type H. pylori (p = 0.04). When only cagA+ H. pylori were considered, s1 vacA type was not associated with disease. In addition, neither the s1a nor s1b subtypes correlated with disease.

CONCLUSIONS

An association between vacA subtypes and disease could not be established in this patient population, due to the strong linkage between vacA s1 type and cagA.

Helicobacter pylori virulence and genetic geography

Isolated for the first time in 1982 from human gastric biopsy, Helicobacter pylori is responsible for gastritis, peptic ulcer, and gastric cancer. A pathogenicity island acquired by horizontal transfer, coding for a type IV secretion system, is a major determinant of virulence. The infection is now treated with antibiotics, and vaccines are in preparation. The geographic distribution suggests coevolution of man and Helicobacter pylori.

Lack of a relationship between Lewis antigen expression and cagA, CagA, vacA and VacA status of Irish Helicobacter pylori isolates

The cagA gene, vacA gene, CagA (cytotoxin-associated gene A product) and VacA (vacuolating cytotoxin) status of a collection of Helicobacter pylori isolates from the geographically distinct Irish population was determined, the potential association of these traits with Lewis (Le) antigen expression was assessed, and the relationship between these bacterial properties and the pathology associated with H. pylori infection was evaluated. Of the 57 isolates, a higher proportion from ulcer than from non-ulcer patients expressed VacA (71% vs. 53%). H. pylori isolates which were cagA-positive were no more significantly associated with peptic ulcers than non-ulcer disease (71% vs. 67%, P = 0.775), nor were CagA-positive isolates (57% vs. 50%, P = 0.783), but 80% of the isolates from duodenal ulcer patients were cagA-positive. Thirty-seven of the 57 isolates were tested for Le antigen expression. No statistically significant relationship (P > 0.05) was found between the occurrence and level of expression of Le(x) or Le(y) and cagA, vacA, or VacA status. This lack of an association in the Irish H. pylori isolates contrasts with that previously reported for predominantly North American isolates, and may be attributable to the adaptation of H. pylori strains with differing attributes to different human populations.

Recombination and clonal groupings within Helicobacter pylori from different geographical regions

A collection of 20 strains of Helicobacter pylori from several regions of the world was studied to better understand the population genetic structure and diversity of this species. Sequences of fragments from seven housekeeping genes (atpA, efp, mutY, ppa, trpC, ureI, yphC ) and two virulence-associated genes (cagA, vacA) showed high levels of synonymous sequence variation (mean percentage Ks of 10-27%) and lower levels of non-synonymous variation (mean percentage Ka of 0.2-5.6%). Cluster analysis of pairwise differences between alleles revealed the existence of two weakly clonal groupings, which included half of the strains investigated. All six strains isolated from Japanese and coastal Chinese were assigned to the 'Asian' clonal grouping, probably reflecting descent from a distinct common ancestor. The clonal groupings were not totally uniform; recombination, as measured by the homoplasy test and compatibility matrices, was extremely common within all genes tested, except cagA. The fact that clonal descent could still be discerned despite such frequent recombination possibly reflects founder effects and geographical separation and/or selection for particular alleles of these genes.

Phenotypic diversity in Lewis expression of Helicobacter pylori isolates from the same host

Populations of Helicobacter pylori cells show a stable expression of Lewis surface antigens, although phase variation may occur among individual organisms grown in vitro. We searched for variation in Lewis phenotypes among H. pylori cells of minimally in vitro-passaged isolates. Lewis expression in 180 clonal H. pylori populations from the primary culture of 20 gastric biopsy samples from 12 patients, and that in 160 isolates from primary cultures from 16 experimentally infected rodents, were examined by enzyme immunoassays. Substantial differences in Lewis expression were found among the isolates from 9 (75%) of 12 patients. These differences were unrelated to overall genetic diversity as determined by polymerase chain reactions for random amplified polymorphic DNA or cagA status, and they persisted during subsequent in vitro passage. In contrast, Lewis expression was highly uniform in H. pylori isolates from different rodents infected for up to 20 weeks. Variation in H. pylori Lewis expression in genetically closely related organisms in human subjects may provide a pool of bacterial phenotypes for the continuous selection of optimally host-adapted populations suitable for persistence.

High prevalence of cagA-positive strains in Helicobacter pylori-infected, healthy, young Chinese adults

BACKGROUND

Cytotoxin-associated gene A (cagA) has been implicated as a potential pathogenic marker for Helicobacter pylori-induced severe gastroduodenal diseases. Although the prevalence of cagA-positive strains has been reported in patient populations from developed countries, only limited information from developing countries is available.

METHODS

Polymerase chain reaction (PCR) in combination with immunoblot analysis was used to determine the prevalence of cagA and its adjacent cagE genes and to evaluate the expression of CagA protein in 55 H. pylori clinical isolates from China.

RESULTS

The expected PCR products derived from H. pylori cagA and cagE genes were identified in all Chinese H. pylori clinical isolates. Similarly, the CagA protein was detected in all 40 isolates tested.

CONCLUSIONS

These results demonstrated that the presence of the cagA gene correlated well with expression of the CagA protein in all surveyed Chinese H. pylori isolates and that infection with cagA-positive H. pylori strains is highly common in China and independent of clinical presentation.

Identification of the minimal intracellular vacuolating domain of the Helicobacter pylori vacuolating toxin

Helicobacter pylori secretes a cytotoxin (VacA) that induces the formation of large vacuoles originating from late endocytic vesicles in sensitive mammalian cells. Although evidence is accumulating that VacA is an A-B toxin, distinct A and B fragments have not been identified. To localize the putative catalytic A-fragment, we transfected HeLa cells with plasmids encoding truncated forms of VacA fused to green fluorescence protein. By analyzing truncated VacA fragments for intracellular vacuolating activity, we reduced the minimal functional domain to the amino-terminal 422 residues of VacA, which is less than one-half of the full-length protein (953 amino acids). VacA is frequently isolated as a proteolytically nicked protein of two fragments that remain noncovalently associated and retain vacuolating activity. Neither the amino-terminal 311 residue fragment (p33) nor the carboxyl-terminal 642 residue fragment (p70) of proteolytically nicked VacA are able to induce cellular vacuolation by themselves. However, co-transfection of HeLa cells with separate plasmids expressing both p33 and p70 resulted in vacuolated cells. Further analysis revealed that a minimal fragment comprising just residues 312-478 functionally complemented p33. Collectively, our results suggest a novel molecular architecture for VacA, with cytosolic localization of both fragments of nicked toxin required to mediate intracellular vacuolating activity.