Helicobacter pylori downregulates expression of human ß-defensin 1 in the gastric mucosa in a type IV secretion-dependent fashion.

Helicobacter pylori establishes a chronic lifelong infection in the human gastric mucosa, which may lead to peptic ulcer disease or gastric adenocarcinoma. The human beta-defensins (hßDs) are antimicrobial peptides, hßD1 being constitutively expressed in the human stomach. We hypothesized that H. pylori may persist, in part, by downregulating gastric hßD1 expression. We measured hßD1 and hßD2 expression in vivo in relation to the presence, density and severity of H. pylori infection, investigated differential effects of H. pylori virulence factors, and studied underlying signalling mechanisms in vitro. Significantly lower hßD1 and higher hßD2 mRNA and protein concentrations were present in gastric biopsies from infected patients. Those patients with higher-level bacterial colonization and inflammation had significantly lower hßD1 expression, but there were no differences in hßD2. H. pylori infection of human gastric epithelial cell lines also downregulated hßD1. Using wild-type strains and isogenic mutants, we showed that a functional cag pathogenicity island-encoded type IV secretion system induced this downregulation. Treatment with chemical inhibitors or siRNA revealed that H. pylori usurped NF-κB signalling to modulate hßD1 expression. These data indicate that H. pylori downregulates hßD1 expression via NF-κB signalling, and suggest that this may promote bacterial survival and persistence in the gastric niche.

Helicobacter pylori-induced peptic ulcer disease is associated with inadequate regulatory T cell responses.

BACKGROUND AND AIMS: Helicobacter pylori infection is the major cause of peptic ulceration and gastric adenocarcinoma. To address the hypothesis that the human acquired immune response to H. pylori influences pathogenesis, we characterised the gastric T helper (Th) and regulatory T cell (Treg) response of infected patients. METHODS: The human gastric CD4(+) T cell response of 28 donors who were infected with H. pylori and 44 who were not infected was analysed using flow cytometry. The T cell associated mucosal cytokine response was analysed by real-time polymerase chain reaction assay of samples from 38 infected and 22 uninfected donors. Recombinant interleukin 10 (IL10) was added to co-cultures of H. pylori and AGS cells and its suppressive effects upon inflammatory responses were measured. RESULTS: We found that the H. pylori-specific response consists of both T helper 1 and 2 subsets with high levels of IL10-secreting Tregs. People with peptic ulcer disease had a 2.4-fold reduced CD4(+)CD25(hi)IL10(+) Treg response (p = 0.05) but increased Th1 and Th2 responses (Th1: 3.2-fold, p = 0.038; Th2: 6.1-fold, p = 0.029) compared to those without ulcers. In vitro studies showed that IL10 inhibited IL8 expression and activation of nuclear factor kappa B induced by H. pylori in gastric epithelial cells, and enhanced H. pylori growth in a bacterial-cell co-culture model. CONCLUSIONS: Together our data suggest that H. pylori induces a regulatory T cell response, possibly contributing to its peaceful coexistence with the human host, and that ulcers occur when this regulatory response is inadequate.

Effects of Helicobacter pylori on the cadherin-catenin complex.

BACKGROUND: The cadherin-catenin complex is the key component of the adherens junction in epithelial cells, and changes in this complex are implicated in gastric adenocarcinoma. Germline mutations in E-cadherin have been described in diffuse-type gastric adenocarcinoma. Helicobacter pylori infection is the first stage in gastric carcinogenesis. AIMS: To determine whether H pylori was associated with changes in the complex, and whether this was affected by virulence of the strain. METHODS: Epithelial cell lines were cultured with H pylori using the wild-type pathogenic and non-pathogenic strains and CagE null and VacA null isogenic mutants. Gastric biopsy specimens at endoscopy were obtained from patients with (n = 17) and without (n = 15) H pylori infection, and E-cadherin and beta-catenin expression was assessed by immunohistochemistry. H pylori was typed by polymerase chain reaction from these patients for CagE and VacA. RESULTS: In vitro studies showed that coculture with a pathogenic strain of H pylori led to disruption of epithelial junctional beta-catenin expression, but without evidence of nuclear translocation or signalling. This effect was independent of a functional Cag pathogenicity island and vacuolating activity, but dependent on live bacteria. No marked differences in beta-catenin or E-cadherin expression were seen in gastric biopsy specimens in patients with and without H pylori infection. CONCLUSION: Acute H pylori infection disrupts junctional beta-catenin in vitro, but chronic infection by H pylori has no effect on E-cadherin and beta-catenin expression, as seen in gastric biopsy specimens at the initial gastritis stage of the proposed Correa pathway of gastric carcinogenesis. A later effect at the later stages of atrophy or intestinal metaplasia cannot be ruled out.

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.

Helicobacter pylori induces cyclooxygenase-1 and cyclooxygenase-2 expression in vascular endothelial cells.

BACKGROUND: Helicobacter pylori induces cyclooxygenase activity in the stomach, although the COX isoform and cellular source are unclear. A potential source is the vascular endothelial cell, which plays a role in regulating mucosal blood flow and inflammatory cell infiltration. METHODS: We examined the effect of four strains (toxigenic and non-toxigenic) of H. pylori on COX isoform expression in vascular endothelial cells. Prostaglandin synthesis was measured by enzyme immunoassay and COX isozyme expression determined by Western blot and RT-PCR. Gene induction was examined using 5' deletion constructs of the COX-1 and COX-2 promoters coupled with luciferase. RESULTS: All H. pylori strains induced prostaglandin generation and expression of both COX-1 and COX-2 in HUVEC, although this was most pronounced with the highly toxigenic strain H. pylori 60190. Treatment of the cells with selective COX inhibitors demonstrated that COX-1 was predominantly responsible for the enhanced generation of prostacyclin induced by H. pylori 60190. Similar results were seen with H. pylori broth culture filtrates, suggesting that a secreted product was responsible. Induction of COX-2 reflected both enhanced gene expression and stabilization of the mRNA. CONCLUSIONS: H. pylori increased both COX-1 and COX-2 activity in vascular endothelial cells. This increased generation of endothelial cell prostacyclin may play a role in modulating mucosal blood flow, platelet function and inflammatory cell infiltration in response to H. pylori infection. The regulation of COX-1 at the transcriptional level by H. pylori described in this study is a novel finding and calls into question the traditional description of COX-1 as a purely constitutive, housekeeping gene.

Helicobacter pylori upregulates matrilysin (MMP-7) in epithelial cells in vivo and in vitro in a Cag dependent manner.

BACKGROUND AND AIMS: Matrix metalloproteinase-7 (MMP-7) is important in normal and pathological remodelling of epithelial-matrix interactions, and is upregulated in gastric cancer. Helicobacter pylori infection is the first stage in gastric carcinogenesis, and therefore our aim was to determine if H pylori upregulated gastric MMP-7 expression and if this was affected by strain virulence. METHODS: We took gastric biopsy specimens at endoscopy from H pylori infected (n = 17) and uninfected (n = 18) patients and assessed MMP-7 expression by ELISA, real time polymerase chain reaction (PCR), and immunohistochemistry (concentrating on epithelial cells in the proliferative zone). We PCR typed H pylori for cagE and vacA. We performed H pylori/cell line coculture studies with wild-type pathogenic and non-pathogenic H pylori strains and with CagE(-) and VacA(-) isogenic mutants. RESULTS: Gastric biopsy specimens from H pylori+ patients expressed higher levels of MMP-7 at the protein and mRNA levels in the antrum and corpus (for example, by ELISA: H pylori+ 0.182 OD units vH pylori- 0.059; p = 0.009 antrum). Epithelial cells from H pylori+ patients stained more intensely for MMP-7 than those from uninfected patients, including in the proliferative zone containing pluripotent cells (p<0.03 antrum, p<0.04 body). Upregulation of MMP-7 in epithelial cells was confirmed at the protein and mRNA levels by H pylori/cell line coculture. These experiments also showed that MMP-7 upregulation was dependent on an intact H pyloricag pathogenicity island but not on the vacuolating cytotoxin. CONCLUSION: We speculate that increased expression of MMP-7 in H pylori gastritis may contribute to gastric carcinogenesis.

Safety and efficacy of 7-day rabeprazole- and omeprazole-based triple therapy regimens for the eradication of Helicobacter pylori in patients with documented peptic ulcer disease.

AIM: A double-blind, randomized study was designed to determine whether rabeprazole- and omeprazole-based triple therapy regimens are therapeutically equivalent in the eradication of Helicobacter pylori. METHODS: Three hundred and forty-five patients with current or previously active peptic ulcer and a positive H. pylori urease test were randomly assigned to receive RCA, OCA, RCM or OCM twice daily for 7 days (R, rabeprazole 20 mg; O, omeprazole 20 mg; C, clarithromycin 500 mg; A, amoxicillin 1000 mg; M, metronidazole 400 mg). H. pylori eradication was documented by negative 13C-urea breath tests at 4 and 12 weeks, and was evaluated using a 2 x 2 factorial design with proton pump inhibitor and antibiotic as factors. RESULTS: Overall eradication rates (per protocol/intention-to-treat) were 87%/77% and 85%/75% with rabeprazole and omeprazole, respectively (not significant). However, a statistical interaction between proton pump inhibitor and antibiotic was identified. RCA produced a somewhat higher eradication rate than OCA (94% vs. 84%; difference, 9.8%; 95% confidence interval, - 0.7% to + 20.4%), whereas RCM produced a lower eradication rate than OCM (79% vs. 86%; difference, 8.1%; 95% confidence interval, - 21.4% to + 5.1%). Ulcer healing rates were > 90% with H. pylori eradication. Each regimen was well tolerated. CONCLUSIONS: Rabeprazole- and omeprazole-based triple therapy regimens are therapeutically equivalent in the eradication of H. pylori and well tolerated. The statistical interaction observed between the proton pump inhibitor and supplementary antibiotic may be due to chance.

Stimulation of adhesion molecule expression by Helicobacter pylori and increased neutrophil adhesion to human umbilical vein endothelial cells.

Helicobacter pylori upregulates endothelial adhesion molecules but the pattern is unclear. Human umbilical vein endothelial cells (HUVEC) were exposed to control medium or H. pylori 60190. Binding of monoclonal antibodies against P-selectin, E-selectin, vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was determined using enzyme-linked immunosorbent assay. Binding of polymorphonuclear leukocytes to HUVEC was determined on cells exposed as above. After 6 h exposure to H. pylori, there were 30%, 124%, 167% and 100% increases in P-selectin, E-selectin, VCAM-1 and ICAM-1 levels and a 400% increase in polymorphonuclear leukocyte adhesion in HUVEC exposed to H. pylori. Effects of incubation for other intervals between 0 and 18 h are also described. H. pylori exerts some of its effects on gastric mucosa via gastric vasculature. This study gives insight into the pattern of H. pylori-associated endothelial adhesion molecule upregulation.

Toxigenic Helicobacter pylori induces changes in the gastric mucosal microcirculation in rats.

BACKGROUND AND AIMS: One of the key components of inflammation is changes in vascular structure and function. This suggests that the microcirculation may be a key target of Helicobacter pylori released factors. It has previously been shown in vivo that pooled H pylori extracts from duodenal ulcer/gastritis patients induce platelet aggregation but no leucocyte activation within rat gastric mucosal microcirculation (GMMC). However, infection with strains associated with ulcer disease as compared with gastritis may exert greater effects on the microcirculation. This study used fluorescent in vivo microscopy to determine the acute effects of extracts of genotypically different H pylori strains on the GMMC. METHODS: Three H pylori extracts, with different cagA and VacA toxigenic status, were individually administered to the gastric mucosa of anaesthetised Wistar rats. The mucosal surface was visualised via an incision made in the exteriorised stomach. Fluoroscein isothiocyanate conjugated to bovine serum albumin (FITC-BSA) or acridine orange was used to quantify macromolecular leak (MML) and leucocyte/platelet activity respectively for 120 minutes. Changes in capillary and post-capillary venule (PCV) diameters were also monitored. RESULTS: The cagA(+) VacA toxigenic strain 60190 induced significant and sustained MML by five minutes (p<0.01). Transient and less leakage was observed with its isogenic VacA(-) mutant and other non-toxigenic strains regardless of cagA status. Significant increases in leucocyte adhesion (p<0.05), platelet aggregation (p<0.05), and PCV vasoconstriction (p<0.05) were only observed with the cag A(+) and toxigenic strain. CONCLUSION: Extracts of H pylori are capable of inducing marked disturbances within the rat GMMC. These disturbances seem to be dependent on the production of an active vacuolating cytotoxin. Varying effects on the GMMC may explain the clinically diverse outcomes associated with genotypically different strains.

Impact of acid secretion, gastritis, and mucus thickness on gastric transfer of antibiotics in rats.

BACKGROUND AND AIMS: The success of Helicobacter pylori eradication regimens depends on gastric pH, inflammation, and mucus thickness. Our aim was to investigate the effects of acid secretion, inflammation, and mucolysis on gastric antibiotic transfer. SUBJECTS AND METHODS: A total of 134 anaesthetised rats were given metronidazole, amoxicillin, or clarithromycin intravenously and gastric contents were aspirated via an indwelling cannula. Acid secretion was controlled by either omeprazole or pentagastrin while gastritis was induced by infection with H pylori or dosing with iodoacetamide. Mucolysis was achieved by instilling pronase into the gastric lumen. RESULTS: Metronidazole transfer increased with acid secretion and fell with omeprazole, independently of gastric pH. Clarithromycin was also transferred with acid but was then rapidly degraded. Omeprazole prevented this degradation, raising gastric luminal concentrations. Omeprazole did not alter amoxicillin transfer. Gastritis induced by H pylori did not alter gastric transfer of metronidazole and amoxicillin but that of clarithromycin was increased by 23%. However, gastritis induced by iodoacetamide reduced clarithromycin transfer without any effect on metronidazole or amoxicillin transfer. Pronase treatment increased amoxicillin transfer fourfold and metronidazole by 66% but reduced clarithromycin transfer by 35%. CONCLUSIONS: Metronidazole and clarithromycin are predominantly transferred with gastric acid rather than by an acid trapping mechanism. Pronase increases the appearance of amoxicillin and metronidazole in gastric secretions.

Interactions between Helicobacter pylori and other risk factors for peptic ulcer bleeding.

AIM: To investigate the role of Helicobacter pylori, expressing the virulence marker CAGA (cytotoxin associated gene product A) in ulcer complications and its interaction with nonsteroidal anti-inflammatory drugs (NSAIDs) and other risk factors. DESIGN: Case control study using conditional logistic regression analysis. SETTING: University and City Hospitals, Nottingham. SUBJECTS: 203 consecutive patients with ulcer bleeding and 203 age- and sex-matched controls. RESULTS: Ulcer bleeding was more likely with positive H. pylori serology (odds ratio = 3.3, 95% CI: 1.7--6.6 for CagA positive, but only OR = 1.6, 95% CI: 0.7-3.7 for CagA negative serology), current smoking (OR 2.2, 95% CI: 1.04-4.7), aspirin < or = 300 mg daily (OR 7.7, 95% CI: 2.8-20.6), all other nonsteroidal anti-inflammatory drugs (NSAIDs: OR 10.6, 95% CI: 3.1-35.7 for < or = 1 defined daily dose lower and OR 22.6, 95% CI: 6.2-82.0 for higher doses) and past ulcer history (OR 5.6, 95% CI: 2.3-14.1). Aspirin < or = 300 mg daily was used by 25.1% of patients vs. 7.4% of controls. Smoking only enhanced risk in the presence of H. pylori, with a synergistic interaction (interaction odds ratio = 4.9, 2.4-9.9, P=0.002). Conversely, risks with non-aspirin NSAIDs were reduced in the presence of H. pylori, particularly if CagA-positive (interaction odds ratio=0.21, 0.05-0.9, P=0.03). CONCLUSIONS: CagA positive H. pylori infection is associated with an increased risk of ulcer bleeding. The risk from non-aspirin NSAIDs is even higher, but is less in H. pylori infected people. Low-dose aspirin is now commonly associated with ulcer bleeding.

Helicobacter pylori genetic diversity within the gastric niche of a single human host.

Isolates of the gastric pathogen Helicobacter pylori harvested from different individuals are highly polymorphic. Strain variation also has been observed within a single host. To more fully ascertain the extent of H. pylori genetic diversity within the ecological niche of its natural host, we harvested additional isolates of the sequenced H. pylori strain J99 from its human source patient after a 6-year interval. Randomly amplified polymorphic DNA PCR and DNA sequencing of four unlinked loci indicated that these isolates were closely related to the original strain. In contrast, microarray analysis revealed differences in genetic content among all of the isolates that were not detected by randomly amplified polymorphic DNA PCR or sequence analysis. Several ORFs from loci scattered throughout the chromosome in the archival strain did not hybridize with DNA from the recent strains, including multiple ORFs within the J99 plasticity zone. In addition, DNA from the recent isolates hybridized with probes for ORFs specific for the other fully sequenced H. pylori strain 26695, including a putative traG homolog. Among the additional J99 isolates, patterns of genetic diversity were distinct both when compared with each other and to the original prototype isolate. These results indicate that within an apparently homogeneous population, as determined by macroscale comparison and nucleotide sequence analysis, remarkable genetic differences exist among single-colony isolates of H. pylori. Direct evidence that H. pylori has the capacity to lose and possibly acquire exogenous DNA is consistent with a model of continuous microevolution within its cognate host.

Conservation of the cag pathogenicity island is associated with vacA alleles and gastroduodenal disease in South African Helicobacter pylori isolates.

BACKGROUND: The development of clinically significant disease in South Africa is associated with the vacuolating cytotoxin gene (vacA) s1 genotype but not with the presence of the cytotoxin associated gene cagA. cagA occurs in >95% of South African isolates and is a variable marker for the entire cag pathogenicity island (PAI). AIM: To characterise the cagPAI in South African isolates and to investigate if structural variants of this multigene locus were associated with variations in vacA status and clinical outcome. PATIENTS AND METHODS: We studied 109 Helicobacter pylori strains (36 from patients with peptic ulceration, 26 with gastric adenocarcinoma, and 47 with no pathology other than gastritis) for differences in selected genes of the cagPAI and alleles of vacA by polymerase chain reaction. RESULTS: All strains were cagA(+). Sixty five (60%) strains had an intact contiguous cagPAI; 78% of peptic ulcer isolates, 73% of gastric adenocarcinoma isolates, but only 40% of gastritis alone isolates (p< 0.01). The entire cagII region was undetectable in 23% of gastritis alone isolates but in only 8% of peptic ulceration isolates (p<0.05). The vacA signal sequence and mid region demonstrated a strong relationship between the virulence associated vacA s1 (p<0.005) and vacA m1 (p=0.05) alleles and an intact cagPAI. CONCLUSION: Although a complete cagPAI was a feature of most infected individuals, deletions in the 5' region of this genetic locus were associated with gastritis alone and with the non-cytotoxic s2/m2 vacA genotype.

Clustering of South African Helicobacter pylori isolates from peptic ulcer disease patients is demonstrated by repetitive extragenic palindromic-PCR fingerprinting.

The present report assesses the association between clonal groupings, disease, and the virulence fingerprint of 76 South African Helicobacter pylori cagA(+) strains isolated from 57 Cape-colored subjects. Two methods, repetitive extragenic palindromic (REP)-PCR and random amplified polymorphic DNA (RAPD)-PCR, were used to generate DNA fingerprints, and computer-assisted analysis was used to derive clusters. The two PCR techniques were only partially complementary (48%). REP-PCR fingerprints identified a distinct pathological cluster consisting of strains from 63% of the patients and was strongly associated with both disease (P < 0.00001) and the vacuolating cytotoxin A (vacA) signal sequence type (P < 0.003). RAPD-PCR fingerprinting was not associated with disease and was less strongly associated with vacA (P < 0.05) than REP-PCR was. Hierarchical analysis indicated that isolates from patients with peptic ulcer disease tended to cluster differently than isolates from patients with gastritis alone or gastric adenocarcinoma. These relationships are consistent with a loosely clonal population structure associated with disease for H. pylori in the Cape-colored population in South Africa.

Effects of genotypically different strains of Helicobacter pylori on human microvascular endothelial cells in vitro.

Helicobacter pylori induces a number of disturbances in rodent gastric microcirculation in vivo. These events may result from direct necrotic or apoptotic damage to endothelial cells. This study therefore aimed to investigate the effects of genotypically different H. pylori strains on microvascular endothelial cell (MVEC) viability in vitro. Four H. pylori extracts were prepared from strains with different cagA or vacA status. MVECs were plated into 96-well plates and coincubated with 50 microl of extract or vehicle for 24, 48, 72, or 96 hr. An MPP assay quantified overall MVEC viability. The dual labeling of MVECs with propidium iodide and Hoechst 33342 distinguished between necrotic and apoptotic cell death, respectively, and allowed total number of viable cells to be determined. All strains of H. pylori decreased cell viability after 72 and 96 hr. Neither necrosis or apoptosis was observed. Counting total number of viable cells revealed decreased cell proliferation with all strains when compared to controls, again reaching significance at 72 and 96 hr. In conclusion, both the MTT assay and the diret cell counting technique demonstrated that all H. pylori strains induced cytostatic but not cytotoxic effects on MVECs. This suggests that microcirculatory disturbances observed in vivo may not be the result of direct endothelial cell damage. However, inhibition of angiogenesis may explain why ulcer healing is delayed in H. pylori-infected patients.

Helicobacter pylori genotypes, host factors, and gastric mucosal histopathology in peptic ulcer disease.

From 183 patients undergoing upper gastrointestinal endoscopy, we used antral and corpus gastric biopsies for bacterial culture and histopathologic examination, blood samples to detect immunoglobulin G antibodies against Helicobacter pylori, and H pylori genomic DNA to analyze cytotoxin-associated gene A (cagA) and vacuolating cytotoxin (vacA) genotypes. As expected, among H pylori biopsy-positive patients, those with duodenal ulcer (DU) (n = 34) had significantly more severe chronic and acute inflammation (P <.001) and epithelial degeneration (P =.004) in the gastric antrum than in the gastric corpus. Each of those 3 parameters and H pylori density were significantly higher in the antrum of patients with DU than in patients with gastric ulcer (GU) or no ulcer. Colonization with vacA s1/cagA-positive strains of H pylori was associated with inflammation and epithelial degeneration in gastric mucosa and increased risk for peptic ulcer disease (PUD), whereas colonization with vacA s2m2/cagA-negative strains was associated with mild gastric histopathology and was not associated with any significant risk for PUD. The predominant H pylori strains in African Americans were vacA s1bm1/cagA-positive, whereas all genotypes were well represented in non-Hispanic-Caucasians. By multivariate analysis, H pylori colonization was significantly associated with DU (Adjusted odds ratio [AdjOR] = 3.2 [1.4-7.2]) and nonsteroidal anti-inflammatory drugs (NSAID) use was inversely associated (AdjOR = 0.3 [0.2-0.7]). NSAID use (AdjOR = 4.3 [1.02-18.5]) and African-American ethnicity (AdjOR = 10.9 [2.6-50]) were significantly associated with GU. Smoking and age were not significantly associated with either DU or GU. These data indicate that DU is associated with an antral-dominant gastritis, and H pylori genotype and NSAID use independently contribute to the pathogenesis of PUD. HUM PATHOL 32:264-273. This is a US Government work. There are no restrictions on its use.

Helicobacter pylori vacA and cagA genotypes in Mexican adults and children.

Studies examining associations between Helicobacter pylori virulence markers and disease have concentrated on adults in developed countries. This study assessed adults and children in Mexico. Ninety patients were recruited, 56 adults (37 with active peptic ulceration and 19 with no ulcers) and 34 children (all with recurrent abdominal pain and no ulcers). H. pylori was cultured from gastric biopsy specimens, and vacA alleles and cagA were typed by use of polymerase chain reaction from multiple colony sweeps. Multiple vacA types were common in single-biopsy isolates and were more frequent in adults with ulcers (95%) than in adults without ulcers (37%; P<.001) or in children (52%; P<.01). vacA s1b and cagA+ strains were more frequent in adults than in children. vacA s1 and cagA+ strains had similar frequencies in adults with and without ulcers. In conclusion, infection with multiple H. pylori strains, defined by different vacA genotypes, is common in Mexico. Such mixed infection is associated with ulcer disease. Strain populations infecting Mexican adults and children differ.