Allelic diversity among Helicobacter pylori outer membrane protein genes homB and homA generated by recombination. J Bacteriol. 2010;192:3961-3968. [PMID: 20525831 DOI: 10.1128/jb.00395-10]

Infiltration to infection: key virulence players of Helicobacter pylori pathogenicity

PURPOSE

This study aims to comprehensively review the multifaceted factors underlying the successful colonization and infection process of Helicobacter pylori (H. pylori), a prominent Gram-negative pathogen in humans. The focus is on elucidating the functions, mechanisms, genetic regulation, and potential cross-interactions of these elements.

METHODS

Employing a literature review approach, this study examines the intricate interactions between H. pylori and its host. It delves into virulence factors like VacA, CagA, DupA, Urease, along with phase variable genes, such as babA, babC, hopZ, etc., giving insights about the bacterial perspective of the infection The association of these factors with the infection has also been added in the form of statistical data via Funnel and Forest plots, citing the potential of the virulence and also adding an aspect of geographical biasness to the virulence factors. The biochemical characteristics and clinical relevance of these factors and their effects on host cells are individually examined, both comprehensively and statistically.

RESULTS

H. pylori is a Gram-negative, spiral bacterium that successfully colonises the stomach of more than half of the world's population, causing peptic ulcers, gastric cancer, MALT lymphoma, and other gastro-duodenal disorders. The clinical outcomes of H. pylori infection are influenced by a complex interplay between virulence factors and phase variable genes produced by the infecting strain and the host genetic background. A meta-analysis of the prevalence of all the major virulence factors has also been appended.

CONCLUSION

This study illuminates the diverse elements contributing to H. pylori's colonization and infection. The interplay between virulence factors, phase variable genes, and host genetics determines the outcome of the infection. Despite biochemical insights into many factors, their comprehensive regulation remains an understudied area. By offering a panoramic view of these factors and their functions, this study enhances understanding of the bacterium's perspective, i.e. H. pylori's journey from infiltration to successful establishment within the host's stomach.

Correlation between the geographical origin of Helicobacter pylori homB-positive strains and their clinical outcomes: a systematic review and meta-analysis

BACKGROUND

In general, all virulence factors of Helicobacter pylori (H. pylori) are involved in its infections. However, recent studies have shown that the homB gene is one of the virulence genes that affects the severity of the clinical results of this bacterium.

METHODS

The main purpose of this study was to investigate the relationship between the presence of homB gene in H. pylori and the progression of its infection to peptic ulcer and gastric cancer. In the present study, we conducted a systematic search to collect all articles related to the effect of homB-positive strains on clinical outcomes. Finally, 12 eligible studies according to our criteria were included in this meta-analysis and the effect of homB gene on gastric ulcer and gastric cancer diseases was evaluated by summary odds ratio (OR).

RESULTS

Current results showed that the homB-positive strains significantly increase the risk of peptic ulcer (OR 1.36; 1.07-1.72 with 95% CIs), especially in western countries (OR 1.61; 1.20-2.14 with 95% CIs). Moreover, we observed a positive association between the homB gene and risk of gastric cancer (OR 2.16; 1.37-3.40 with 95% CIs). In addition, based on subgroup analysis, it was found that the presence of this gene in H. pylori strains increases the risk of gastric cancer in the Asian population (OR 3.71; 1.85-7.45 with 95% CIs).

CONCLUSIONS

Overall, in the present study we found that homB gene is responsible for the progressing of primary infection to severe complications, in particular peptic ulcer in western countries and gastric cancer in Asian countries.

Virulence of Helicobacter pylori outer membrane proteins: an updated review

Helicobacter pylori (H. pylori) infection is associated with some gastric diseases, such as gastritis, peptic ulcer, and gastric cancer. CagA and VacA are known virulence factors of H. pylori, which play a vital role in severe clinical outcomes. Additionally, the expression of outer membrane proteins (OMPs) helps H. pylori attach to gastric epithelial cells at the primary stage and increases the virulence of H. pylori. In this review, we have summarized the paralogs of H. pylori OMPs, their genomic loci, and the different receptors of OMPs identified so far. We focused on five OMPs, BabA (HopS), SabA (HopP), OipA (HopH), HopQ, and HopZ, and one family of OMPs: Hom. We highlight the coexpression of OMPs with other virulence factors and their relationship with clinical outcomes. In conclusion, OMPs are closely related to the pathogenic processes of adhesion, colonization, persistent infection, and severe clinical consequences. They are potential targets for the prevention and treatment of H. pylori–related diseases.

Helicobacter pylori virulence genes

Helicobacter pylori (H. pylori) is one of the most important human pathogens, infecting approximately half of the global population. Despite its high prevalence, only a subset of H. pylori infected individuals develop serious gastroduodenal pathology. The pathogenesis of H. pylori infection and disease outcome is thus thought to be mediated by an intricate interplay between host, environmental and bacterial virulence factors. H. pylori has adapted to the harsh milieu of the human stomach through possession of various virulence genes that enable survival of the bacteria in the acidic environment, movement towards the gastric epithelium, and attachment to gastric epithelial cells. These virulence factors enable successful colonization of the gastric mucosa and sustain persistent H. pylori infection, causing chronic inflammation and tissue damage, which may eventually lead to the development of peptic ulcers and gastric cancer. Numerous studies have focused on the prevalence and role of putative H. pylori virulence genes in disease pathogenesis. While several virulence factors with various functions have been identified, disease associations appear to be less evident, especially among different study populations. This review presents key findings on the most important H. pylori virulence genes, including several bacterial adhesins and toxins, in children and adults, and focuses on their prevalence, clinical significance and potential relationships.

ArsRS-Dependent Regulation of homB Contributes to Helicobacter pylori Biofilm Formation

One elusive area in the Helicobacter pylori field is an understanding of why some infections result in gastric cancer, yet others persist asymptomatically for the life-span of the individual. Even before the genomic era, the high level of intraspecies diversity of H. pylori was well recognized and became an intriguing area of investigation with respect to disease progression. Of interest in this regard is the unique repertoire of over 60 outer membrane proteins (OMPs), several of which have been associated with disease outcome. Of these OMPs, the association between HomB and disease outcome varies based on the population being studied. While the molecular roles for some of the disease-associated OMPs have been evaluated, little is known about the role that HomB plays in the H. pylori lifecycle. Thus, herein we investigated homB expression, regulation, and contribution to biofilm formation. We found that in H. pylori strain G27, homB was expressed at a relatively low level until stationary phase. Furthermore, homB expression was suppressed at low pH in an ArsRS-dependent manner; mutation of arsRS resulted in increased homB transcript at all tested time-points. ArsRS regulation of homB appeared to be direct as purified ArsR was able to specifically bind to the homB promoter. This regulation, combined with our previous finding that ArsRS mutations lead to enhanced biofilm formation, led us to test the hypothesis that homB contributes to biofilm formation by H. pylori. Indeed, subsequent biofilm analysis using a crystal-violet quantification assay and scanning electron microscopy (SEM) revealed that loss of homB from hyper-biofilm forming strains resulted in reversion to a biofilm phenotype that mimicked wild-type. Furthermore, expression of homB in trans from a promoter that negated ArsRS regulation led to enhanced biofilm formation even in strains in which the chromosomal copy of homB had been deleted. Thus, homB is necessary for hyper-biofilm formation of ArsRS mutant strains and aberrant regulation of this gene is sufficient to induce a hyper-biofilm phenotype. In summary, these data suggest that the ArsRS-dependent regulation of OMPs such as HomB may be one mechanism by which ArsRS dictates biofilm development in a pH responsive manner.

Comparative analysis of the Hom family of outer membrane proteins in isolates from two geographically distinct regions: The United States and South Korea

BACKGROUND

Helicobacter pylori encodes numerous outer membrane proteins (OMPs), but only a few have been characterized in depth. Deletion, duplication, and allelic variation of many of the H. pylori OMPs have been reported, which suggests that these proteins may play key roles in host adaptation. Herein, we characterize the variation observed within the Hom family of OMPs in H. pylori obtained from two geographically distinct populations.

MATERIALS AND METHODS

PCR genotyping of the hom genes was carried out using clinical isolates from South Korea and the United States. A combination of statistical, phylogenetic, and protein modeling analyses was conducted to further characterize the hom variants.

RESULTS

Variations in the closely related hom genes, homA and homB, occur in regions that are predicted to encode environmentally exposed loops. A similar phenomenon is true for homC^S as compared to homC^L . Conversely, little variation was observed in homD. Certain variants of the Hom family of proteins were more prominent in isolates from the Korean population as compared to isolates from the United States.

CONCLUSION

En masse, our data show that the homA, homB, and homC profiles vary based upon the geographic origin of the strain; however, the fourth member of the hom family, homD, is more highly conserved. Additionally, protein topology modeling showed that many of the less well-conserved regions between homA and homB and between homC^S and homC^L corresponded to predicted environmentally exposed loops, suggesting that the divergence of the Hom family may be due to host adaptation/pressure.

Immune Evasion Strategies and Persistence of Helicobacter pylori

Helicobacter pylori infection is commonly acquired during childhood, can persist lifelong if not treated, and can cause different gastric pathologies, including chronic gastritis, peptic ulcer disease, and eventually gastric cancer. H. pylori has developed a number of strategies in order to cope with the hostile conditions found in the human stomach as well as successful mechanisms to evade the strong innate and adaptive immune responses elicited upon infection. Thus, by manipulating innate immune receptors and related signaling pathways, inducing tolerogenic dendritic cells and inhibiting effector T cell responses, H. pylori ensures low recognition by the host immune system as well as its persistence in the gastric epithelium. Bacterial virulence factors such as cytotoxin-associated gene A, vacuolating cytotoxin A, or gamma-glutamyltranspeptidase have been extensively studied in the context of bacterial immune escape and persistence. Further, the bacterium possesses other factors that contribute to immune evasion. In this chapter, we discuss in detail the main evasion and persistence strategies evolved by the bacterium as well as the specific bacterial virulence factors involved.

Gene polymorphisms of pathogenic Helicobacter pylori in patients with different types of gastrointestinal diseases

Helicobacter pylori (H. pylori) is a kind of chronic infectious pathogen which can cause chronic gastritis, peptic ulcer, gastric cancer and other diseases. The genetic structure of the pathogenic genes of H. pylori varies largely, which contributes to the differences in virulence among various strains, and in clinical symptoms. Virulence genes of H. pylori can be categorized into three main classes: those related to adhesion and colonization, those related to gastric mucosal injury, and others. This review focuses on the relationship between genetic polymorphisms of the three classes of virulence genes of H. pylori and diseases. Most of the genetic polymorphisms of the main virulence factors of H. pylori are summarized in this paper.

The Role of Helicobacter pylori Outer Membrane Proteins in Adherence and Pathogenesis

Helicobacter pylori is one of the most successful human pathogens, which colonizes the mucus layer of the gastric epithelium of more than 50% of the world’s population. This curved, microaerophilic, Gram-negative bacterium induces a chronic active gastritis, often asymptomatic, in all infected individuals. In some cases, this gastritis evolves to more severe diseases such as peptic ulcer disease, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. H. pylori has developed a unique set of factors, actively supporting its successful survival and persistence in its natural hostile ecological niche, the human stomach, throughout the individual’s life, unless treated. In the human stomach, the vast majority of H. pylori cells are motile in the mucus layer lining, but a small percentage adheres to the epithelial cell surfaces. Adherence to the gastric epithelium is important for the ability of H. pylori to cause disease because this intimate attachment facilitates: (1) colonization and persistence, by preventing the bacteria from being eliminated from the stomach, by mucus turnover and gastric peristalsis; (2) evasion from the human immune system and (3) efficient delivery of proteins into the gastric cell, such as the CagA oncoprotein. Therefore, bacteria with better adherence properties colonize the host at higher densities. H. pylori is one of the most genetically diverse bacterial species known and is equipped with an extraordinarily large set of outer membrane proteins, whose role in the infection and persistence process will be discussed in this review, as well as the different receptor structures that have been so far described for mucosal adherence.

Novel functions for glycosyltransferases Jhp0562 and GalT in Lewis antigen synthesis and variation in Helicobacter pylori

Lewis (Le) antigens are fucosylated oligosaccharides present in the Helicobacter pylori lipopolysaccharide. Expression of these antigens is believed to be important for H. pylori colonization, since Le antigens also are expressed on the gastric epithelia in humans. A galactosyltransferase encoded by β-(1,3)galT is essential for production of type 1 (Le(a) and Le(b)) antigens. The upstream gene jhp0562, which is present in many but not all H. pylori strains, is homologous to β-(1,3)galT but is of unknown function. Because H. pylori demonstrates extensive intragenomic recombination, we hypothesized that these two genes could undergo DNA rearrangement. A PCR screen and subsequent sequence analyses revealed that the two genes can recombine at both the 5' and 3' ends. Chimeric β-(1,3)galT-like alleles can restore function in a β-(1,3)galT null mutant, but neither native nor recombinant jhp0562 can. Mutagenesis of jhp0562 revealed that it is essential for synthesis of both type 1 and type 2 Le antigens. Transcriptional analyses of both loci showed β-(1,3)galT expression in all wild-type (WT) and mutant strains tested, whereas jhp0562 was not expressed in jhp0562 null mutants, as expected. Since jhp0562 unexpectedly displayed functions in both type 1 and type 2 Le synthesis, we asked whether galT, part of the type 2 synthesis pathway, had analogous functions in type 1 synthesis. Mutagenesis and complementation analysis confirmed that galT is essential for Le(b) production. In total, these results demonstrate that galT and jhp0562 have functions that cross the expected Le synthesis pathways and that jhp0562 provides a substrate for intragenomic recombination to generate diverse Le synthesis enzymes.

Genotypic and phenotypic variation of Lewis antigen expression in geographically diverse Helicobacter pylori isolates

BACKGROUND

Helicobacter pylori are a persistent colonizer of the human gastric mucosa, which can lead to the development of peptic ulcer disease and gastric adenocarcinomas. However, H. pylori can asymptomatically colonize a host for years. One factor that has been hypothesized to contribute to such persistence is the production of Lewis (Le) antigens in the lipopolysaccharide layer of the bacterial outer membrane as a form of molecular mimicry, because humans also express these antigens on their gastric mucosa. Humans and H. pylori both are polymorphic for Le expression, which is driven in H. pylori by variation at the Le synthesis loci. In this report, we sought to characterize Le genotypic and phenotypic variation in geographically diverse H. pylori isolates.

MATERIALS AND METHODS

From patients undergoing endoscopy in 29 countries, we determined Le phenotypes of 78 H. pylori strains and performed genotyping of the galT and β-(1,3)galT loci in 113 H. pylori strains.

RESULTS

Le antigen phenotyping revealed a significant (p < .0001) association between type 1 (Le(a) and Le(b) ) expression and strains of East Asian origin. Genotyping revealed a significant correlation between strain origin and the size of the promoter region upstream of the Le synthesis gene, galT (p < .0001).

CONCLUSION

These results indicate that the heterogeneity of human Le phenotypes is reflected in their H. pylori colonizing strains and suggest new loci that can be studied to assess the variation of Le expression.

Helicobacter pylori homB, but not cagA, is associated with gastric cancer in Iran

While several distinct virulence factors of Helicobacter pylori have been shown to be associated with different clinical outcomes, there is still much to learn about the role of different bacterial factors in gastric carcinogenesis. This study looked at the distribution of the cagA, homA, and homB genes in strains isolated from patients suffering from gastroduodenal diseases in Iran and assessed if there was any association between disease state and the presence of the aforementioned virulence factors. Genomic DNA from 138 H. pylori strains was isolated and genotyped via PCR. Strains were obtained from dyspeptic patients (35 from gastritis patients, 62 from peptic ulcer patients, and 41 from gastric cancer patients) at the Teaching Touba Clinic and Imam Hospital of the Mazandaran University of Medical Sciences in Sari, Iran. The overall prevalence rates of cagA, homA, and homB were 58%, 54%, and 43%, respectively. Stratification of patients showed a significant difference in the prevalence of H. pylori virulence genes across the disease states. The frequency of homB was statistically significantly higher in gastric cancer patients (78%) than in patients suffering from peptic ulcers (20%) or gastritis (43%) (P < 0.0001). The presence of homB was also associated with the presence of cagA (r = 0.243). These data suggest that in this population the presence of homB may be a predictor of more virulent strains of H. pylori and influence the severity of disease manifestation.

New implications on genomic adaptation derived from the Helicobacter pylori genome comparison

Background

Helicobacter pylori has a reduced genome and lives in a tough environment for long-term persistence. It evolved with its particular characteristics for biological adaptation. Because several H. pylori genome sequences are available, comparative analysis could help to better understand genomic adaptation of this particular bacterium.

Principal Findings

We analyzed nine H. pylori genomes with emphasis on microevolution from a different perspective. Inversion was an important factor to shape the genome structure. Illegitimate recombination not only led to genomic inversion but also inverted fragment duplication, both of which contributed to the creation of new genes and gene family, and further, homological recombination contributed to events of inversion. Based on the information of genomic rearrangement, the first genome scaffold structure of H. pylori last common ancestor was produced. The core genome consists of 1186 genes, of which 22 genes could particularly adapt to human stomach niche. H. pylori contains high proportion of pseudogenes whose genesis was principally caused by homopolynucleotide (HPN) mutations. Such mutations are reversible and facilitate the control of gene expression through the change of DNA structure. The reversible mutations and a quasi-panmictic feature could allow such genes or gene fragments frequently transferred within or between populations. Hence, pseudogenes could be a reservoir of adaptation materials and the HPN mutations could be favorable to H. pylori adaptation, leading to HPN accumulation on the genomes, which corresponds to a special feature of Helicobacter species: extremely high HPN composition of genome.

Conclusion

Our research demonstrated that both genome content and structure of H. pylori have been highly adapted to its particular life style.