Recently, numerous publications on Helicobacter pylori (H. pylori) have been published, but bibliometric analyses on this research field are scarce. To address this gap, we conducted a bibliometric analysis to provide a comprehensive overview and to explore the current research states and hotspots in this field.

Publications on H. pylori from 2002 to 2021 were retrieved from the Web of Science Core Collection database (WoSCC). Trends in publications and citations were analyzed using Excel 2021. VOSviewer and Citespace were used to perform bibliometrics analysis.

36,266 publications on H. pylori were retrieved from the WoSCC database. In general, we observed an increasing trend in the number of publications over the past 20 years. The United States was the most productive and influential country, with the largest proportion of both publications and total citations. Helicobacter, US Department of Veterans Affairs, and Graham, David were the most productive journals, institutions and authors, respectively. Further analysis the co-occurrence and burst detection of keywords revealed that the most common keywords were "Helicobacter pylori," "gastric cancer," and "gastritis," all keywords were divided into eight main clusters, and the most important current research hotspot was the relationship between H. pylori infection and the changes of gut microbiota.

The United States has been the most productive and influential country on H. pylori research, and H. pylori-related research remains an active research field. The relationship between H. pylori infection and the changes of gut microbiota is a research hotspot attracting significant attention.

Helicobacter pylori produces outer membrane vesicles (OMV), delivering bacterial substances including the oncogenic cytotoxin-associated CagA protein to their surroundings. We investigated the effects of H. pylori OMV carrying CagA (OMV-CagA) on cell junctions and ATP-binding proteome of epithelial monolayers, using proteomics, mass spectrometry and imaging. OMV-CagA localized in close vicinity of ZO-1 tight junction protein and induced histone H1 binding to ATP. We suggest the expression of novel events in the interactions between H. pylori OMV and epithelia, which may have an influence on host gene transcription and lead to different outcomes of an infection and development of cancer.

Gastric infection by Helicobacter pylori is the most common cause of ulcer disease and gastric cancer. The mechanism of progression from gastritis and inflammation to ulcers and cancer in a fraction of those infected is not definitively known. Significant acidity is unique to the gastric environment and is required for ulcer development. The interplay between gastric acidity and H. pylori pathogenesis is important in progression to advanced disease. The aim of this study was to characterize the impact of acid on gastric epithelial integrity and cytokine release and how H. pylori infection alters these responses. Human gastric epithelial (HGE-20) cells were grown on porous inserts, and survival, barrier function, and cytokine release were studied at various apical pH levels in the presence and absence of H. pylori. With apical acidity, gastric epithelial cells demonstrate increased barrier function, as evidenced by increased transepithelial electrical resistance (TEER) and decreased paracellular permeability. This effect is reduced in the presence of wild-type, but not urease knockout, H. pylori. The epithelial inflammatory response is also modulated by acidity and H. pylori infection. Without H. pylori, epithelial IL-8 release decreases in acid, while IL-6 release increases. In the presence of H. pylori, acidic pH diminishes the magnitude of the previously reported increase in IL-8 and IL-6 release. H. pylori interferes with the gastric epithelial response to acid, contributing to altered barrier function and inflammatory response. H. pylori diminishes acid-induced tightening of cell junctions in a urease-dependent manner, suggesting that local pH elevation promotes barrier compromise and progression to mucosal damage.

To investigate Helicobacter pylori (H. pylori) CagA diversity and to evaluate the association between protein polymorphisms and the occurrence of gastric pathologies.

One hundred and twenty-two clinical isolates of H. pylori cultured from gastric biopsies obtained from Colombian patients with dyspepsia were included as study material. DNA extracted from isolates was used to determine cagA status, amplifying the C-terminal cagA gene region by polymerase chain reaction. One hundred and six strains with a single amplicon were sequenced and results were used to characterize the 3' variable region of the cagA gene. To establish the number and type of tyrosine phosphorylation motifs Glutamine acid-Proline-Isoleucine-Tyrosine-Alanine (EPIYA) bioinformatic analysis using Amino Acid Sequence Analyzer-Amino Acid Sequence Analyzer software was conducted. Analysis of the association between the number of EPIYA motifs and the gastric pathology was performed using chi(2) test and analysis of the presence of EPIYA-C motifs in relation to the pathology was made by logistic regression odds ratios. Comparisons among EPIYA types found and those reported in GenBank were performed using a proportion test in Statistix Analytical Software version 8.0.

After amplification of the 3' of the cagA gene, 106 from 122 isolates presented a single amplicon and 16 showed multiple amplicons. As expected, diversity in the size of the cagA unique fragments among isolates was observed. The 106 strains that presented a single amplicon after 3' cagA amplification came from patients with gastritis (19 patients), atrophic gastritis (21), intestinal metaplasia (26), duodenal ulcer (22) and gastric cancer. DNA sequence analysis showed that the differences in size of 3' cagA unique fragments was attributable to the number of EPIYA motifs: 1.9% had two EPIYA motifs, 62.3% had three, 33.0% had four and 2.8% had five motifs. The majority of tested clinical strains (62.3%) were found to harbor the ABC combination of EPIYA motifs and a significant statistical difference was observed between the frequencies of ABCC tyrosine phosphorylation motifs and Western strains sequences deposited in GenBank.

The present report describes a lack of association between H. pylori CagA-protein polymorphisms and pathogenesis. ABCC high frequency variations compared with Western-strains sequences deposited in GenBank require more investigation.

Clarithromycin is one of the antibiotics used for the treatment of Helicobacter pylori infections, and clarithromycin resistance is the most important factor when it comes to predicting eradication failure. The present study analyzed H. pylori isolates for the presence of 23S rRNA gene mutations and determined the risk factors associated with resistance among H. pylori isolates collected in Madrid, Spain, in 2008. We studied 118 H. pylori strains isolated from the same number of patients. A total of 76.3% of the patients were born in Spain, 52.7% were children, 20.3% had previously been treated, and 66.1% were female. Clarithromycin resistance was determined by Etest. H. pylori strains were considered resistant if the MIC was ≥1 mg/liter. DNA extraction was carried out by use of the NucliSens easyMAG platform with NucliSens magnetic extraction reagents (bioMérieux). The DNA sequences of the 23S rRNA genes of clarithromycin-resistant and -sensitive strains were determined to identify specific point mutations. The vacA genotype and cagA status were determined by PCR. We found that 42 (35.6%) strains were resistant to clarithromycin by Etest. Etest results were confirmed by detection of the presence of point mutations in 34 (88.1%) of these strains. Eight H. pylori strains were resistant to clarithromycin by Etest but did not have a point mutation in the 23S rRNA gene. Mutation at A2143G was found in 85.3% of the strains, mutation at A2142G in 8.8%, and mutation at T2182C in 5.9%. Dual mutations were found in 8.8% of the strains. H. pylori clarithromycin-resistant strains were strongly associated with pediatric patients, with patients born in Spain, and with patients who had previously been treated (P ≤ 0.02). In addition, H. pylori strains resistant to clarithromycin more frequently presented the vacA s2/m2 genotype and were more likely to be cagA negative than susceptible strains (39.1% and 11.2%, respectively; P value < 0.001). We concluded that, in the present study, H. pylori clarithromycin-resistant strains are more frequently found in children, in patients mostly born in Spain, and in individuals who were previously treated for H. pylori infection and that these individuals are more likely colonized with a less virulent H. pylori strain.

Infection with Helicobacter pylori is a major cause of gastric cancer (GC). The association likely has been underestimated in the past due to disease-related clearance of the infection. On the other hand, only a minority of the infected individuals develop GC, and better risk stratification is therefore highly desirable. We aimed to assess the association of GC with antibodies to 15 individual H. pylori proteins, determined by novel multiplex serology, to identify potentially relevant risk markers. This analysis was based on 123 GC cases aged 50 to 74 years and 492 age-matched and sex-matched controls from Saarland, Germany. Eight of the antibodies were significantly associated with noncardia GC and seven of them were significantly related to GC at any site. More pronounced associations were observed for noncardia GC; adjusted odds ratios (95% confidence intervals) ranged from 1.60 (1.01-2.54) for HyuA to 5.63 (3.20-9.91) for cytotoxin-associated antigen A (CagA). A dose-response relationship was found between the number of seropositivities and GC (P < 0.001). The seropositivities of CagA and GroEL were found to be independent predictors of GC, which were strongly related to GC risk in a dose-response manner (P < 0.001). In conclusion, GroEL was identified as a new independent risk marker that may contribute to enhanced quantification of H. pylori-related GC risk.

We initiated this study to investigate whether combining Helicobacter pylori eradication with immunosuppressive therapy provides an additional benefit to patients with idiopathic thrombocytopenic purpura (ITP) that has relapsed or has not responded to steroid and/or danazol therapy in patients who have H. pylori infection. Thirty- four patients with chronic ITP that had relapsed or failed to steroid and/or danazol therapy were assessed for H. pylori infection. Of the 21 confirmed cases, 12 patients were given H. pylori eradication therapy alone (EA), while 9 patients received eradication therapy combined with immunosuppressive therapy (EI). The response rate was not significantly different between patients in the EA and those in the EI group (41.7% in the EA group vs. 66.7% in the EI group, p=0.345). The median platelet count at 6 months after therapy was higher in the EI group patients (75 x 10(9)/L in the EI group patients vs. 18 x 10(9)/L in the EA group patients, p=0.028). The median response duration was also longer in the EI group patients (9 months in the EI group patients vs. 3 months in the EA group patients, p=0.049). These results show that a significant benefit is gained by the use of H. pylori eradication combined with immunosuppressive therapy over the use of eradication therapy alone for patients with chronic ITP.

Helicobacter pylori cagA and vacA genotypes have been used for almost a decade as stable entities to link the severity of gastritis and ulcer disease. We describe here microevolution of the two genomic islands, cag pathogenicity island (cagPAI; 40 kb) and tfs3 (16 kb) from isolates obtained at inclusion (one subclone) and after a 10-year period (two subclones) from a duodenal ulcer patient. Our results indicate microevolution in cagA, cagE, and cag7 genes of the cagPAI and open reading frames G, P, and L in tfs3, which possibly leads to inactivation or pseudogenization of these genes. Interestingly, no significant reduction in the severity of gastroduodenal pathology was found. These results point to an obvious difficulty in correlating the continuously evolving virulence factors such as the cagPAI genes with disease characteristics that appear to remain stable.

We examined the kinetics of IL-8 production and CagA status in AGS infected with Helicobacter pylori, 26695 (Western CagA-type), HPK5 (Eastern CagA-type) and isogenic cagA-disrupted mutants, exposed to different pH (pH 6 and pH 3). IL-8 was produced in the early and late phases after infection in CagA-dependent and -independent manners, respectively, irrespective of CagA-type. The wild-type exposed to low pH tremendously reduced IL-8 level at early phase, but restored with urea, suggesting that low pH exerted the kinetics of H. pylori-induced IL-8 production in CagA-dependent manner and urea was necessary for effective induction. CagA and phosphorylated CagA increased time-dependently after infection. Phosphorylated CagA from 26695, but not HPK5, rapidly peaked, consistent with the kinetics of IL-8 induction and appearance of hummingbird phenotype. ATF3 transcripts peaked late phase by wild-type, however, induced in two peaks early and late phases by cagA-disrupted mutants, indicating that different CagA-type proteins altered ATF3 induction in the infected cells.

Thailand has the lowest incidence of gastric cancer in the world. Helicobacter pylori infection, a low serum pepsinogen I/II ratio, and interleukin (IL)-1beta-511 polymorphisms are suspected to be risk factors for gastric cancer.

A total of 167 Thais, comprising 56 cancer patients and 111 volunteers without cancer, underwent an esophagogastroduodenoscopic examination and three fixed-point biopsies; a cancer tissue biopsy was also done, and blood samples were collected. The subjects without cancer were divided into normal subjects and chronic gastritis patients. IL-1beta-511 polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism, and the serum levels of pepsinogen I and II were determined by a radioimmunoassay. Helicobacter pylori IgG antibody and tissue pathology were tested in all groups.

The pepsinogen I/II ratio was significantly lower in the gastric cancer group than in the normal and chronic gastritis groups [odds ratio (OR), 2.3; 95% confidence interval (CI), 1.10-4.80; P = 0.025]. Gastric cancer patients were positive for the H. pylori IgG antibody more frequently than negative (OR, 2.946; 95% CI, 1.4-6.39; P = 0.005). However, only 15 (27%) cancer patients were both positive for H. pylori IgG antibody and had low serum pepsinogen I/II. The C/C genotype was found more frequently in the gastric cancer group than in the group with a normal gastric mucosa (OR, 0.64; 95% CI, 0.50-0.81; P = 0.014).

A low serum pepsinogen I/II ratio combined with positivity for H. pylori IgG, and a IL-1beta-511 C/C genotype may be independent risk factors for gastric cancer in Thais.

It has been suggested that Helicobacter pylori eradication often increases platelet counts in patients with chronic idiopathic thrombocytopenic purpura (ITP). In addition, H. pylori has been shown to induce platelet activation (CD62p or P-selectin expression) in previous studies. We assessed the response of platelet count and CD62p expression after eradication therapy in patients with ITP and H. pylori infection.

We prospectively studied 15 ITP patients diagnosed with H. pylori infection by serology and breath test. A follow-up breath test was used to document eradication. Two out of 15 patients showed improvement in platelet counts after 6 months, 1 of which may have had drug-induced thrombocytopenia. Overall, certain platelet response rate in our series was 6.7% (1/15). We found that platelet CD62p expression by flow cytometry was elevated in 10/15 (66.7%) H. pylori-infected patients, which is a statistically significant difference when compared with 3/33 (9.1%) control ITP patients seronegative for H. pylori (p = 0.002). In addition, eradication therapy decreased CD62p expression (p = 0.04). However, reduction in platelet activation was not associated with an increase in platelet counts (mean 72.4 x 10(9)/l before and 68.7 after therapy; p = 0.4).

In our series, platelet activation was common in ITP patients with H. pylori, and eradication therapy decreased platelet activation but seldom increased platelet counts. Increased platelet CD62p expression is a putative link between chronic infections and atherosclerosis, but further study is needed to clarify the implications of our observation.

Virulence factors are related to the ability of a microbe to induce disease. True virulence factors must therefore have a disease association, an in-vivo correlate with disease such as increased mucosal inflammation, or both.

The cytotoxin-associated gene pathogenicity island; the outer membrane inflammatory protein; the duodenal ulcer-promoting gene, and possibly the blood group antigen-binding adhesion, are the only factors that to date qualify as virulence factors. Numerous recent studies have investigated the interaction of vacuolating cytotoxin A or cytotoxin-associated gene A with cells and cell lines in vitro. It remains unclear, however, whether any of the findings, for example, in-vitro experiments showing that vacuolating cytotoxin A affect the regulation of T or B lymphocytes, have an in-vivo counterpart, or play any role in disease pathogenesis.

The criteria for a virulence factor include evidence of an association with a disease or a disease surrogate such as the severity of mucosal inflammation, epidemiologic consistency, and biologic plausibility. Confirmation of the proposed mechanism requires elimination of the effect by gene deletion and restoration by complementation. Cytotoxin-associated gene A has been the subject of elegant biochemistry despite lack of evidence that it is involved in pathogenesis. The current focus of research on Helicobacter pylori relates to exploring the biology of Helicobacter pylori, often using systems that only vaguely relate to the in-vivo conditions or to disease pathogenesis.

The cytotoxin-associated gene (cag) pathogenicity island (PAI) is important for the virulence of Helicobacter pylori. In this study, we have compared the complete nucleotide sequence of the cag PAI in four clinical isolates. These isolates were selected from patients matched for age and sex from the same geographical region. The patients suffered from either gastric cancer (Ca52 and Ca73) or duodenal ulcer (Du23:2 and Du52:2). All four strains induced an interleukin (IL)-8 response in AGS cells and translocated CagA into host cells where the protein was tyrosine phosphorylated, and thus harboured a functional type IV secretion system encoded by the cag PAI. The cagA gene contains a variable region close to its 3' end. Different compositions of this region has been proposed to exert various degrees of morphological changes in cultured gastric epithelial cells, and there are indications that the structure of the repetitive region is connected to the severity of disease. One of the studied strains (Du23:2) possessed five Western-type repeat regions while the other three strains harboured one Western-type repeat. Strain Du23:2 also contained a major rearrangement or large insertion/duplication in the intergenic region between HP0546 and HP0547 (cagA). Sequence similar to that of genes HP0510 and HP0509 was found in the 5' end of this region. The 3' end was similar to the corresponding region of strain ATCC 43504, including a mini IS605 element and a duplication of the 3' end of the cag PAI. Finally, a novel gene was identified in the cag PAI in three of the sequenced strains at the position of HP0521. This gene, HP0521B, is present in approximately half of Swedish H. pylori isolates.

Helicobacter pylori is the causative agent of a variety of gastric diseases, but the clinical relevance of bacterial virulence factors is still controversial. Virulent strains carrying the cag pathogenicity island (cagPAI) are thought to be key players in disease development. Here, we have compared cagPAI-dependent in vitro responses in H. pylori isolates obtained from 75 patients with gastritis, peptic ulcer, and gastric cancer (n = 25 in each group). AGS gastric epithelial cells were infected with each strain and assayed for (i) CagA expression, (ii) translocation and tyrosine phosphorylation of CagA, (iii) c-Src inactivation, (iv) cortactin dephosphorylation, (v) induction of actin cytoskeletal rearrangements associated with cell elongation, (vi) induction of cellular motility, and (vii) secretion of interleukin-8. Interestingly, we found high but similar prevalences of all of these cagPAI-dependent host cell responses (ranging from 56 to 80%) among the various groups of patients. This study revealed CagA proteins with unique features, CagA subspecies of various sizes, and new functional properties for the phenotypic outcomes. We further showed that induction of AGS cell motility and elongation are two independent processes. Our data corroborate epidemiological studies, which indicate a significant association of cagPAI presence and functionality with histopathological findings in gastritis, peptic ulcer, and gastric cancer patients, thus emphasizing the importance of the cagPAI for the pathogenicity of H. pylori. Nevertheless, we found no significant association of the specific H. pylori-induced responses with any particular patient group. This may indicate that the determination of disease development is highly complex and involves multiple bacterial and/or host factors.

Cag pathogenicity island-containing Helicobacter pylori (type I) induces signal transduction pathways resulting in tyrosine phosphorylation of proteins adjacent to the site of bacterial adhesion on host gastric epithelial cells. Conventional block PCR-restriction fragment length polymorphism (RFLP) and real-time LightCycler (LC) PCR hybridization assays, validated by direct sequencing, were designed to test for the presence of three nucleotide sequences corresponding to tyrosine phosphorylation motifs (TPMs) A, B, and C in 84 isolates of H. pylori type I from patients in England. Overall, the PCR assays demonstrated that one or more TPMs were present in 62 strains (75%). Motif A was common (71% of strains), whereas motifs B and C were rarer (8% of strains). Strains lacking a TPM were typically vacuolating cytotoxin genotype vacA m2. Motif A was widely distributed in relation to disease severity and was more commonly (but not significantly [P = 0.071]) associated with gastric ulcer than with duodenal ulcer (86 versus 56%). The LC hybridization assay provided a rapid means of detecting all three motifs, but RFLP analysis was more specific for TPM-A. TPMs provide novel additional strain markers for defining cagA variation, including identification of RFLP types within TPM-A. The presence of a particular TPM was not of direct diagnostic value, either singly or in combination, but the higher proportion of TPM-A strains in gastric ulcer patients merits further investigation.

Tyrosine phosphorylation of Helicobacter pylori cytotoxin-associated protein of in gastric epithelial cells is reported. The goals of this study are first to examine the occurrence of CagA tyrosine phosphorylation in H. pylori strains isolated from patients with gastric adenocarcinoma and gastritis, and second to clarify the relationship between the diversity of tyrosine phosphorylation motifs and the presence of CagA tyrosine phosphorylation.

Fifty-eight clinical isolates of H. pylori from patients with gastric adenocarcinoma (29 cases) and gastritis (29 cases) were studied for CagA tyrosine phosphorylation by Western blotting. Sequence diversity of tyrosine phosphorylation motifs was analysed among positive- or negative-CagA tyrosine phosphorylation isolates.

Positive CagA tyrosine phosphorylation was found in 93.1% (27 of 29) of strains from gastric adenocarcinoma patients and 51.7% (15 of 29) of strains from gastritis patients (p < 0.001). Intact motifs were found in H. pylori isolates with CagA tyrosine phosphorylation. Of the 16 negative CagA tyrosine phosphorylation isolates, intact tyrosine phosphorylation motifs were found in 15 isolates.

CagA tyrosine phosphorylation, which is significantly greater in strains from gastric adenocarcinoma patients, may play a role in gastric carcinogenesis, and could be a better marker of more virulent strains than the cag pathogenicity island in Asia, where the cag pathogenicity island is present in nearly all H. pylori strains. Sequence diversity of tyrosine phosphorylation motifs on CagA was not related to the presence of tyrosine phosphorylation. The absence of tyrosine phosphorylation motif might result in negative tyrosine phosphorylation phenotypes, but such motifs are not the sole factors associated with CagA tyrosine phosphorylation.

It has been suggested that enzyme immunoassay (EIA) kits validated in one region may yield variable diagnostic performance results in different regions, possibly due to strain-specific differences in antibody responses in different populations. We tested (13)C-urea breath test-characterized serum samples from 109 U.S. patients and 288 Japanese patients using enzyme immunoassay with different preparations of high-molecular-weight cell-associated (HM-CAP) antigens that are conserved across Helicobacter pylori strains. Replicate antigens were prepared from five H. pylori clinical isolates. Eight antigen preparations were evaluated: two of U.S. origin and six of Japanese origin. The accuracies achieved with the eight antigen preparations ranged from 94.4 to 96.3% with the U.S. samples. With the Japanese samples the accuracies achieved ranged from 92.3 to 97.2%. Use of a pool of HM-CAP antigens prepared from isolates from Japan resulted in a higher median enzyme immunoassay value and slightly fewer samples with indeterminate results compared to the results obtained by use of the U.S. standard HM-CAP antigen for H. pylori-positive patients (accuracies, 97.2 and 92.3%, respectively), suggesting that variations in performance between both antigen source and patient population might be reduced by using antigens pooled from several strains.

Five years after publication of the complete genome sequence of Helicobacter pylori, research interest is shifting from the descriptive association of virulence factors with clinical outcome in infected patients to the molecular mechanisms of virulence factor action. This is particularly noticeable for VacA and CagA, for both of which detailed understanding of the interaction with host signalling pathways has accumulated over the last year. The role of H. pylori Lewis antigens for clinical outcome was further substantiated. Various strategies of H. pylori to fool or evade the human immune system are described, which all lead to the dysfunction of specific compartments of the host cellular immune system. Finally, a number of animal models indicate that inflammation is a key factor for gastric carcinogenesis, which is finally supported by a large prospective study identifying corpus atrophy and intestinal metaplasia as precancerous conditions.