Pathogenesis of Helicobacter pylori Infection

The clinical outcome of Helicobacter pylori infection is determined by a complex scenario of interactions between the bacterium and the host. The main bacterial factors associated with colonization and pathogenicity comprise outer membrane proteins including BabA, SabA, OipA, AlpA/B, as well as the virulence factors CagA in the cag pathogenicity island ( cag PAI) and the vacuolating cytotoxin VacA. The multitude of these proteins and allelic variation makes it extremely difficult to test the contribution of each individual factor. Much effort has been put into identifying the mechanism associated with H. pylori -associated carcinogenesis. Interaction between bacterial factors such as CagA and host signal transduction pathways seems to be critical for mediating the induction of membrane dynamics, actin-cytoskeletal rearrangements and the disruption of cell-to-cell junctions as well as proliferative, pro-inflammatory and antiapoptotic nuclear responses. An animal model using the Mongolian gerbil is a useful system to study the gastric pathology of H. pylori infection.     

Helicobacter pylori cag pathogenicity island-positive strains induce syndecan-4 expression in gastric epithelial cells

Helicobacter pylori is recognized as the main cause of gastritis and is associated with gastric carcinogenesis. Syndecan-4 represents the major source of heparan sulfate (HS) in the gastric cells. HS proteoglycans expressed on the cell surface constitute targets for H. pylori at the early stage of infection. The aim of this study was to determine whether H. pylori induction of syndecan-4 expression is affected by the virulence characteristics of the infecting strain, namely the cytotoxic-associated gene ( cag ) pathogenicity island (PAI). We observed that individuals infected with highly pathogenic H. pylori strains express syndecan-4 in the foveolar epithelium of the gastric mucosa. The association between the cag PAI status of the infecting strain and syndecan-4 expression was further demonstrated by infection of gastric epithelial cell lines with a panel of cag PAI⁺ and cag PAI⁻ H. pylori strains, showing that expression of syndecan-4 was significantly increased in response to infection with the highly pathogenic strains. Moreover, infection of gastric cells with cag A and cag E mutant strains further confirmed that syndecan-4 induction is dependent on an intact cag PAI. The present study shows that highly pathogenic H. pylori strains induce syndecan-4 expression, both in human gastric mucosa and in gastric cell lines, in a cag PAI-dependent manner.     

Importance of EGF receptor, HER2/Neu and Erk1/2 kinase signalling for host cell elongation and scattering induced by the Helicobacter pylori CagA protein: antagonistic effects of the vacuolating cytotoxin VacA

Helicobacter pylori is the causative agent of gastric pathologies ranging from chronic gastritis to peptic ulcers and even cancer. Virulent strains carrying both the cag pathogenicity island ( cag PAI) and the vacuolating cytotoxin VacA are key players in disease development. The ca gPAI encodes a type IV secretion system (T4SS) which forms a pilus for injection of the CagA protein into gastric epithelial cells. Injected CagA undergoes tyrosine phosphorylation and induces actin-cytoskeletal rearrangements involved in host cell scattering and elongation. We show here that the CagA-induced responses can be inhibited in strains expressing highly active VacA. Further investigations revealed that VacA does not interfere with known activities of phosphorylated CagA such as inactivation of Src kinase and cortactin dephosphorylation. Instead, we demonstrate that VacA exhibits inactivating activities on the epidermal growth factor receptor EGFR and HER2/Neu, and subsequently Erk1/2 MAP kinase which are important for cell scattering and elongation. Inactivation of vacA gene, downregulation of the VacA receptor RPTP-α, addition of EGF or expression of constitutive-active MEK1 kinase restored the capability of H. pylori to induce the latter phenotypes. These data demonstrate that VacA can downregulate CagA's effects on epithelial cells, a novel molecular mechanism showing how H. pylori can avoid excessive cellular damage.     

Evidence for Transepithelial Dendritic Cells in Human H. pylori Active Gastritis

Background:  Despite extensive experimental investigation stressing the importance of bacterial interaction with dendritic cells (DCs), evidence regarding direct interaction of Helicobacter pylori or its virulence products with DCs in the human gastric mucosa is lacking.
Methods:  Human gastric mucosa biopsies, with or without H. pylori infection and active inflammation, were investigated at light and electron microscopy level with immunocytochemical tests for bacterial products (VacA, urease, outer membrane proteins) and DC markers (DC-SIGN, CD11c, CD83) or with the DC-labeling ZnI₂-OsO₄ technique. Parallel tests with cultured DCs were carried out.
Results:  Cells reproducing ultrastructural and cytochemical patterns of DCs were detected in the lamina propria and epithelium of heavily infected and inflamed (but not of normal) mucosa, where DC luminal endings directly contact H. pylori and take up their virulence products. Cytotoxic changes (mitochondrial swelling, cytoplasmic vacuolation, autophagy) were observed in intraepithelial DCs and reproduced in cultured DCs incubated with H. pylori broth culture filtrates to obtain intracellular accumulation of VacA and urease. Granulocytes were also seen to contact and heavily phagocytose luminal H. pylori , while macrophages remained confined to basal epithelium, though taking up bacteria and bacterial products.
Conclusion:  Human DCs can enter H. pylori -infected gastric epithelium, in association with other innate immunity cells, to take up bacteria and their virulence products. This process is likely to be important for bacterial sensing and pertinent immune response; however, it may also generate DC cytotoxic changes potentially hampering their function.     

Negative selection of T cells by Helicobacter pylori as a model for bacterial strain selection by immune evasion.

The majority of humans infected with Helicobacter pylori maintain a lifelong infection with strains bearing the cag pathogenicity island (PAI). H. pylori inhibits T cell responses and evades immunity so the mechanism by which infection impairs responsiveness was investigated. H. pylori caused apoptotic T cell death, whereas Campylobacter jejuni did not. The induction of apoptosis by H. pylori was blocked by an anti-Fas Ab (ZB4) or a caspase 8 inhibitor. In addition, a T cell line with the Fas rendered nonfunctional by a frame shift mutation was resistant to H. pylori-induced death. H. pylori strains bearing the cag PAI preferentially induced the expression of Fas ligand (FasL) on T cells and T cell death, whereas isogenic mutants lacking these genes did not. Inhibiting protein synthesis blocked FasL expression and apoptosis of T cells. Preventing the cleavage of FasL with a metalloproteinase inhibitor increased H. pylori-mediated killing. Thus, H. pylori induced apoptosis in Fas-bearing T cells through the induction of FasL expression. Moreover, this effect was linked to bacterial products encoded by the cag PAI, suggesting that persistent infection with this strain may be favored through the negative selection of T cells encountering specific H. pylori Ags.     

Emergence of recombinant strains of Helicobacter pylori during human infection

Genetic recombination can be important evolutionarily in speeding the adaptation of organisms to new environments and in purging deleterious mutations. Here, we describe polymerase chain reaction (PCR), hybridization and DNA sequence-based evidence of six such exchanges between two strains of Helicobacter pylori during natural mixed infection of a patient in Lithuania. One parent strain contained the 37 kb long, virulence-associated cag pathogenicity island (PAI), and the other strain lacked this PAI. Most H. pylori from the patient had descended from the cag ⁺ parent, but had become cag ⁻ during infection. This had resulted from transfer of DNA containing the 'empty site' allele from the cag ⁻ strain and homologous recombination, not from excision of the cag PAI without DNA transfer. Other cases of recombination involved genes for an outer membrane protein ( omp 5 and omp 29; also called HP0227 and HP1342) and a putative phosphoenolpyruvate synthase ( ppsA  ; HP0121). Replacement of a short patch of DNA sequence (36–124 bp) was also seen. As the chance of forming any given recombinant is small, the abundance of recombinants in this patient suggests selection for particular recombinant genotypes during years of chronic infection. We suggest that genetic exchange among unrelated H. pylori strains, as documented here, is important because of the diversity of this gastric pathogen and its human hosts. Certain H. pylori recombinants may grow better in a given host than either parent. The vigour of growth, in turn, could impact on the severity of disease that infection can elicit.     

Helicobacter pylori strains expressing the vacuolating cytotoxin interrupt phagosome maturation in macrophages by recruiting and retaining TACO (coronin 1) protein

Recent evidence suggests that persistence of Helicobacter pylori can be explained, at least in part, by the failure of macrophages to kill bacteria. The fate of type 1 H. pylori strain LC11, which expresses the cag pathogenicity island (PAI) and the vacuolating cytotoxin, and type 2 strain LC20, which lacks both these virulence factors, was determined following infection of the murine macrophage cell line RAW 264.7 or the human macrophage-like cell line THP-1. Helicobacter pylori strain LC11 displayed enhanced survival in macrophages in comparison with strain LC20 (4.0 +/- 0.2 versus 2.1 +/- 0.6 log CFU ml-1, P < 0.01) at 24 h. Phagosomes containing strain LC11 showed reduced co-localization with LysoTracker Red, higher levels of expression of the early endosome marker EEA1 expression and lower expression of the late endosome/lysosome marker LAMP1 relative to internalized strain LC20, both at 2 h and 24 h. These findings indicate that, in contrast to strain LC20, strain LC11 resides in a compartment with early endosome properties and does not fuse with lysosomes. In addition, phagosomes containing LC11 recruited and retained a higher percentage of TACO (coronin 1) protein in comparison with phagosomes containing strain LC20. Furthermore, IFN-gamma stimulation facilitated maturation of phagosomes containing strain LC11 in association with the release of TACO and a reduction in bacterial survival. We have demonstrated through the use of isogenic cagA-, cagE-/picB- and vacA- mutant strains, that VacA plays a significant role in the interruption of the phagosome maturation. Taken together, these results indicate that, following phagocytosis, H. pylori strains expressing the vacuolating cytotoxin arrest phagosome maturation in association with the retention of TACO.     

Helicobacter pylori-induced homotypic phagosome fusion in human monocytes is independent of the bacterial vacA and cag status

Following reports that a VacA+cag+ toxigenic but not a VacA-cag- non-toxigenic Helicobacter pylori strain induced homotypic phagosome fusion in murine macrophages, we addressed that phenomenon in human cells. Mononuclear phagocytes and epitheloid cells were challenged with H. pylori strains of different vacA and cag genotypes and with VacA- and Cag- isogenic mutants, and chased in the absence or presence of signal transduction modulators. Electron microscopy revealed that, in monocytes: (i) homotypic phagosome fusion was frequently induced by all live H. pylori strains investigated but not by exogenous VacA; (ii) phagosomes containing bacteria fused, but not those containing latex beads; (iii) fusion resulted in communal compartments resembling giant multivesicular bodies; and (iv) formation of these compartments was blocked by inhibiting the host cell regulators PI 3-kinase, phospholipase C and p42 MAP kinase. Whereas some internalized bacteria remained viable 1 h after uptake, none survived a 24 h period. In contrast to monocytes, infected epitheloid cells rarely developed communal compartments. In combination, these results demonstrate that, in human monocytes, the H. pylori-induced homotypic phagosome fusion depends on neither the vacuolating cytotoxin VacA nor the cag pathogenicity island of H. pylori and does not result in prolonged intracellular survival.     

Subproteomes of soluble and structure-bound Helicobacter pylori proteins analyzed by two-dimensional gel electrophoresis and mass spectrometry

Helicobacter pylori is one of the most common bacterial pathogens and causes a variety of diseases, such as peptic ulcer or gastric cancer. Despite intensive study of this human pathogen in the last decades, knowledge about its membrane proteins and, in particular, those which are putative components of the type IV secretion system encoded by the cag pathogenicity island (PAI) remains limited. Our aim is to establish a dynamic two-dimensional electrophoresis-polyacrylamide gel electrophoresis (2-DE-PAGE) database with multiple subproteomes of H. pylori (http://www.mpiib-berlin.mpg.de/2D-PAGE) which facilitates identification of bacterial proteins important in pathogen-host interactions. Using a proteomic approach, we investigated the protein composition of two H. pylori fractions: soluble proteins and structure-bound proteins (including membrane proteins). Both fractions differed markedly in the overall protein composition as determined by 2-DE. The 50 most abundant protein spots in each fraction were identified by peptide mass fingerprinting. We detected four cag PAI proteins, numerous outer membrane proteins (OMPs), the vacuolating cytotoxin VacA, other potential virulence factors, and few ribosomal proteins in the structure-bound fraction. In contrast, catalase (KatA), gamma-glutamyltranspeptidase (Ggt), and the neutrophil-activating protein NapA were found almost exclusively in the soluble protein fraction. The results presented here are an important complement to genome sequence data, and the established 2-D PAGE maps provide a basis for comparative studies of the H. pylori proteome. Such subproteomes in the public domain will be effective instruments for identifying new virulence factors and antigens of potential diagnostic and/or curative value against infections with this important pathogen.     

Clinical and pathological importance of cagA-positive Helicobacter pylori strains in children with abdominal complaints

Background. The aim of this study was to assess the correlation between the prevalence of Helicobacter pylori strains possessing cytotoxin-associated gene A ( cag A) in children and the intensity of clinical complaints and morphological changes of the gastric mucosa.
Materials and Methods. A group of 80 children with gastrointestinal complaints was included in this study. Pathologists examined mucosal biopsy specimens from these patients. The urease test and multiplex polymerase chain reaction (MPCR) were used to identify H. pylori strains.
Results. In the group of children infected with cag A-positive H. pylori strains, fourth-degree gastritis was more frequent than in the group with cag A-negative H. pylori colonization. In histopathological assessment, infection with cag A-positive H. pylori was associated also with higher grades of inflammatory intensity and activity.
Conclusions. Marked inflammation of the antral mucosa was significantly more frequent in children infected with cag A-positive H. pylori than in those infected with cag A-negative H. pylori , as assessed endoscopically and histopathologically. No specific symptoms for cag A-positive and cag A-negative H. pylori infection were observed.     

Reduced activation of inflammatory responses in host cells by mouse-adapted Helicobacter pylory isolates

Helicobacter pylori strains that harbour the Cag pathogenicity island (Cag PAI) induce interleukin (IL)-8 secretion in gastric epithelial cells, via the activation of NF- kappa B, and are associated with severe inflammation in humans. To investigate the influence of Cag PAI-mediated inflammatory responses on H. pylori adaptation to mice, a selection of H. pylori clinical isolates (n = 12) was cag PAI genotyped and tested in co-culture assays with AGS gastric epithelial cells, and in mouse colonization studies. Six isolates were shown to harbour a complete cag PAI and to induce NF- kappa B activation and IL-8 secretion in AGS cells. Of the eight isolates that spontaneously colonized mice, six had a cag PAI(-) genotype and did not induce pro-inflammatory responses in these cells. Mouse-to-mouse passage of the two cag PAI(+) -colonizing strains yielded host-adapted variants that infected mice with bacterial loads 100-fold higher than those of the respective parental strains (P= 0.001). These mouse-adapted variants were affected in their capacity to induce pro-inflammatory responses in host cells, yet no changes in cag PAI gene content were detected between the strains by DNA microarray analysis. This work provides evidence for in vivo selection of H. pylori bacteria with a reduced capacity to induce inflammatory responses and suggests that such bacteria are better adapted to colonize mice.     

The effect of the cag pathogenicity island on binding of Helicobacter pylori to gastric epithelial cells and the subsequent induction of apoptosis

BACKGROUND: Helicobacter pylori infection leads to gastritis, peptic ulcer, and gastric cancer, in part due to epithelial damage following bacteria binding to the epithelium. Infection with cag pathogenicity island (PAI) bearing strains of H. pylori is associated with increased gastric inflammation and a higher incidence of gastroduodenal diseases. It is now known that various effector molecules are injected into host epithelial cells via a type IV secretion apparatus, resulting in cytoskeletal changes and chemokine secretion. Whether binding of bacteria and subsequent apoptosis of gastric epithelial cells are altered by cag PAI status was examined in this study. METHODS: AGS, Kato III, and N87 human gastric epithelial cell lines were incubated with cag PAI-positive or cag PAI-negative strains of H. pylori in the presence or absence of clarithromycin. Binding was evaluated by flow cytometry and scanning electron microscopy. Apoptosis was assessed by detection of DNA degradation and ELISA detection of exposed histone residues. RESULTS: cag PAI-negative strains bound to gastric epithelial cells to the same extent as cag PAI-positive strains. Both cag PAI-positive and cag PAI-negative strains induced apoptosis. However, cag PAI-positive strains induced higher levels of DNA degradation. Incubation with clarithromycin inactivated H. pylori but did not affect binding. However, pretreatment with clarithromycin decreased infection-induced apoptosis. CONCLUSIONS: cag PAI status did not affect binding of bacteria to gastric epithelial cells but cag PAI-positive H. pylori induced apoptosis more rapidly than cag PAI-negative mutant strains, suggesting that H. pylori binding and subsequent apoptosis are differentially regulated with regard to bacterial properties.     

Cag pathogenicity island-independent up-regulation of matrix metalloproteinases-9 and -2 secretion and expression in mice by Helicobacter pylori infection

Helicobacter pylori cag pathogenicity island (PAI) is a major determinant of gastric injury via induction of several matrix metalloproteinases (MMPs). In the present study, we examined the influence of the cag PAI on gastric infection and MMP-9 production in mice and in cultured cells. A new mouse colonizing Indian H. pylori strain (AM1) that lacks the cag PAI was used to study the cag PAI importance in inflammation. Groups of C57BL/6 mice were inoculated separately with H. pylori strains AM1 and SS1 (cag+), gastric tissues were histologically examined, and bacterial colonization was scored by quantitative culture. Mice infected with either cag+ or cag- H. pylori strains showed gastric inflammation and elevated MMP-3 production. Significant up-regulation of pro-MMP-9 secretion and gene expression in H. pylori infected gastric tissues indicate dispensability of cag PAI for increased pro-MMP-9 secretion and synthesis in mice. In agreement, cell culture studies revealed that both AM1 and SS1 were equipotent in pro-MMP-9 induction in human gastric epithelial cells. Both strains showed moderate increase in MMP-2 activity in vivo and in vitro. In addition, increased secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 induced pro-MMP-9 secretion and synthesis in AM1 or SS1 strain-infected mice suggesting elicitation of pro-inflammatory cytokines by both cag- and cag+ genotype. Moreover, tissue inhibitors of metalloproteinase-1 expression were decreased with increase in pro-MMP-9 induction. These data show that H. pylori may act through different pathways other than cag PAI-mediated for gastric inflammation and contribute to up-regulation of MMP-9 via pro-inflammatory cytokines.     

Helicobacter pylori Multiplex Serology

Background:  Helicobacter pylori infection is associated with severe gastrointestinal disease including cancer. It induces complex antibody responses that might vary depending on disease state but currently cannot be assessed adequately. The objective of this work was the development of a sensitive and specific H. pylori multiplex serology assay with high-throughput capability that allows simultaneous detection of antibodies to a protein array.
Methods:  Seventeen proteins of up to three H. pylori strains (26695, G27, 151), including CagA, VacA, UreA, Catalase, Omp, and GroEL, were recombinantly expressed as glutathione- S -transferase fusion proteins, affinity-purified, and used as antigens in a fluorescent bead-based antibody-binding assay. Reference sera (n   =   317) characterized by commercial assays (screening ELISA with Western blot confirmation) were used for validation.
Results:  H. pylori seropositivity by multiplex serology defined as reactivity with at least four proteins showed good agreement (kappa: 0.70) with commercial serologic assay classification, and a sensitivity of 89% and specificity of 82%. For individual antigens, agreement with Western blot was good for CagA (kappa: 0.77), moderate for UreA (kappa: 0.53), and weak for VacA (kappa: 0.12). Of the 13 proteins expressed from two strains, only VacA showed serologic strain differences. High antibody reactivity to CagA (Type I infection) was negatively associated with antibodies to GroEL, Cad, CagM, catalase, HcpC, NapA, and UreA, suggesting type-specific differences in protein expression patterns and/or immune response.
Conclusion:  With its high-throughput and simultaneous detection abilities, H. pylori multiplex serology appears suited as tool for large seroepidemiologic studies assessing H. pylori prevalence, antibody patterns, and associations with specific diseases.     

Cutting edge: urease release by Helicobacter pylori stimulates macrophage inducible nitric oxide synthase

Inducible NO synthase (iNOS) expression and production of NO are both up-regulated with Helicobacter pylori infection in vivo and in vitro. We determined whether major pathogenicity proteins released by H. pylori activate iNOS by coculturing macrophages with wild-type or mutant strains deficient in VacA, CagA, picB product, or urease (ureA(-)). When filters were used to separate H. pylori from macrophages, there was a selective and significant decrease in stimulated iNOS mRNA, protein, and NO(2)(-) production with the ureA(-) strain compared with wild-type and other mutants. Similarly, macrophage NO(2)(-) generation was increased by H. pylori protein water extracts of all strains except ureA(-). Recombinant urease stimulated significant increases in macrophage iNOS expression and NO(2)(-) production. Taken together, these findings indicate a new role for the essential H. pylori survival factor, urease, implicating it in NO-dependent mucosal damage and carcinogenesis.     

HIV protease inhibitors attenuate adherence of Candida albicans to epithelial cells in vitro

The cagA gene is a key marker for the Helicobacter pylori cag pathogenicity island (PAI), which may vary in composition in different strains with insertion sequence mediated interruptions and deletions of genes. While presence of cagA has been associated with increased risk for peptic ulcer disease and gastric cancer, the precise link with virulence is controversial. We investigated H. pylori from dyspeptics in one location in England (mid-Essex) with reference to the prevalence and distribution by age cohort of different cag PAI forms to determine if presence of the insertion element IS605 had a modifying effect on the severity of associated disease. H. pylori isolated from gastric biopsies over a 4-year period were screened by specific PCR assays for the presence of cagA, cagD, cagE and virD4 genes in the cag PAI, and for the presence of IS605 in the PAI and elsewhere in the genome. Most (68%) of the 166 isolates of H. pylori contained a PAI based on detection of cagA whereas 29% had no detectable PAI using multiple loci. The cagA+ genotype frequencies were similar in the peptic ulcer and non-ulcer dyspepsia-gastritis groups (79% vs. 74%) whereas frequencies in the NUD-oesophagitis and normal mucosa groups were lower (58%) but not significantly different (P>0.41). Genomic IS605 inserts were present at an overall frequency of 32% and were widely distributed with respect to patient age and disease severity. The combined cagA+/IS- strain genotype was common but not significantly associated with PUD compared to endoscopically normal mucosa (P> or =0.807). We concluded that presence of the IS605 element, whether in cagA+ or cagA- strains of H. pylori, did not systematically modify the severity of associated disease in the study population.     

Translocation of the Helicobacter pylori CagA protein in gastric epithelial cells by a type IV secretion apparatus

Helicobacter pylori is one of the most common bacterial pathogens, infecting about 50% of the world population. The presence of a pathogenicity island (PAI) in H. pylori has been associated with gastric disease. We present evidence that the H. pylori protein encoded by the cytotoxin-associated gene A ( cagA ) is translocated and phosphorylated in infected epithelial cells. Two-dimensional gel electrophoresis (2-DE) of proteins isolated from infected AGS cells revealed H. pylori strain-specific and time-dependent tyrosine phosphorylation and dephosphorylation of several 125–135 kDa and 75–80 kDa proteins. Immunoblotting studies, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), cell fractionation and confocal microscopy demonstrated that one of the 125–135 kDa proteins represents the H. pylori CagA protein, which is translocated into the host cell membrane and the cytoplasm. Translocation of CagA was dependent on functional cagA gene and virulence ( vir ) genes of a type IV secretion apparatus composed of virB4 , virB7 , virB10 , virB11 and virD4 encoded in the cag PAI of H. pylori . Our findings support the view that H. pylori actively translocates virulence determinants, including CagA, which could be involved in the development of a variety of gastric disease.     

OipA plays a role in Helicobacter pylori-induced focal adhesion kinase activation and cytoskeletal re-organization

The initial signalling events leading to Helicobacter pylori infection associated changes in motility, cytoskeletal reorganization and elongation of gastric epithelial cells remain poorly understood. Because focal adhesion kinase (FAK) is known to play important roles in regulating actin cytoskeletal organization and cell motility we examined the effect of H. pylori in gastric epithelial cells co-cultured with H. pylori or its isogenic cag pathogenicity island (PAI) or oipA mutants. H. pylori induced FAK phosphorylation at distinct tyrosine residues in a dose- and time-dependent manner. Autophosphorylation of FAK Y397 was followed by phosphorylation of Src Y418 and resulted in phosphorylation of the five remaining FAK tyrosine sites. Phosphorylated FAK and Src activated Erk and induced actin stress fibre formation. FAK knock-down by FAK-siRNA inhibited H. pylori- mediated Erk phosphorylation and abolished stress fibre formation. Infection with oipA mutants reduced phosphorylation of Y397, Y576, Y577, Y861 and Y925, inhibited stress fibre formation and altered cell morphology. cag PAI mutants reduced phosphorylation of only FAK Y407 and had less effect on stress fibre formation than oipA mutants. We propose that activation of FAK and Src are responsible for H. pylori -induced induction of signalling pathways resulting in the changes in cell phenotype important for pathogenesis.