Genome Sequences of Three hpAfrica2 Strains of Helicobacter pylori

Helicobacter pylori in Human Stomach: The Inconsistencies in Clinical Outcomes and the Probable Causes

Pathogenic potentials of the gastric pathogen, Helicobacter pylori, have been proposed, evaluated, and confirmed by many laboratories for nearly 4 decades since its serendipitous discovery in 1983 by Barry James Marshall and John Robin Warren. Helicobacter pylori is the first bacterium to be categorized as a definite carcinogen by the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO). Half of the world’s population carries H. pylori, which may be responsible for severe gastric diseases like peptic ulcer and gastric cancer. These two gastric diseases take more than a million lives every year. However, the role of H. pylori as sole pathogen in gastric diseases is heavily debated and remained controversial. It is still not convincingly understood, why most (80–90%) H. pylori infected individuals remain asymptomatic, while some (10–20%) develop such severe gastric diseases. Moreover, several reports indicated that colonization of H. pylori has positive and negative associations with several other gastrointestinal (GI) and non-GI diseases. In this review, we have discussed the state of the art knowledge on “H. pylori factors” and several “other factors,” which have been claimed to have links with severe gastric and duodenal diseases. We conclude that H. pylori infection alone does not satisfy the “necessary and sufficient” condition for developing aggressive clinical outcomes. Rather, the cumulative effect of a number of factors like the virulence proteins of H. pylori, local geography and climate, genetic background and immunity of the host, gastric and intestinal microbiota, and dietary habit and history of medicine usage together determine whether the H. pylori infected person will remain asymptomatic or will develop one of the severe gastric diseases.

Genomic analysis of Helicobacter himalayensis sp. nov. isolated from Marmota himalayana

Background

Helicobacter himalayensis was isolated from Marmota himalayana in the Qinghai-Tibet Plateau, China, and is a new non-H. pylori species, with unclear taxonomy, phylogeny, and pathogenicity.

Results

A comparative genomic analysis was performed between the H. himalayensis type strain 80(YS1)^T and other the genomes of Helicobacter species present in the National Center for Biotechnology Information (NCBI) database to explore the molecular evolution and potential pathogenicity of H. himalayensis. H. himalayensis 80(YS1)^T formed a clade with H. cinaedi and H. hepaticus that was phylogenetically distant from H. pylori. The H. himalayensis genome showed extensive collinearity with H. hepaticus and H. cinaedi. However, it also revealed a low degree of genome collinearity with H. pylori. The genome of 80(YS1)^T comprised 1,829,936 bp, with a 39.89% GC content, a predicted genomic island, and 1769 genes. Comparatively, H. himalayensis has more genes for functions in “cell wall/membrane/envelope biogenesis” and “coenzyme transport and metabolism” sub-branches than the other compared helicobacters, and its genome contained 42 virulence factors genes, including that encoding cytolethal distending toxin (CDT).

Conclusions

We characterized the H. himalayensis 80(YS1)^T genome, its phylogenetic position, and its potential pathogenicity. However, further understanding of the pathogenesis of this potentially pathogenic bacterium is required, which might help to manage H. himalayensis-induced diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07245-y.

Detection of Helicobacter pylori and its virulence genes (cagA, dupA, and vacA) among patients with gastroduodenal diseases in Chris Hani Baragwanath Academic Hospital, South Africa

BACKGROUND

The global prevalence of H. pylori approaches 50%, with prevalence rates between 20 and 40% in developed countries and up to 90% in Africa and other developing nations of the world. Development of H. pylori-associated diseases is determined by a number of virulence factors. This study aimed at determining the prevalence of H. pylori infections and virulence genes (cagA, dupA, and vacA); the relationship between virulence factors and gastroduodenal diseases among patients.

METHODS

Gastric biopsies were obtained from patients and cultured, DNA was extracted from cultured isolates and biopsies for PCR assay after which samples were investigated using standard laboratory procedures. Data of associated risk factors were obtained with the aid of questionnaires.

RESULTS

Of the 444 participants, H. pylori was detected in 115 (25.9%) from culture analysis and 217 (48.9%) by direct PCR method. Ninety-eight (85.2%) of the culture-positive patients were also detected by PCR giving an overall prevalence of 52.7% (234/444). The highest number of H. pylori isolates 76.9% (180/234) was obtained from patients suffering from pangastritis. The CagA virulence gene was found in 62% (145/234), dupA in 53.4% (125/234) and vacA in 90.6% (212/234). VacA genotype s1 m1 was the most prevalent [56.4% (132)] followed by s2 m2 [11.5% (27)], s2 m1 [10.3% (24)] and [s1 m2 9.4% (22)]. There was a significant association observed in vacA s1 and peptic ulcer disease, as well as vacA s1/m2 and gastric erosion (P < 0.05).

CONCLUSION

The study revealed a significant association between virulence genes and the development of certain forms of gastric infections while the variations in H. pylori detection and the associated risk factors investigated in the study were not significantly related.

A Novel Approach to Helicobacter pylori Pan-Genome Analysis for Identification of Genomic Islands

Genomes of a given bacterial species can show great variation in gene content and thus systematic analysis of the entire gene repertoire, termed the pan-genome, is important for understanding bacterial intra-species diversity, population genetics, and evolution. Here, we analyzed the pan-genome from 30 completely sequenced strains of the human gastric pathogen Helicobacter pylori belonging to various phylogeographic groups, focusing on 991 accessory (not fully conserved) orthologous groups (OGs). We developed a method to evaluate the mobility of genes within a genome, using the gene order in the syntenically conserved regions as a reference, and classified the 991 accessory OGs into five classes: Core, Stable, Intermediate, Mobile, and Unique. Phylogenetic networks based on the gene content of Core and Stable classes are highly congruent with that created from the concatenated alignment of fully conserved core genes, in contrast to those of Intermediate and Mobile classes, which show quite different topologies. By clustering the accessory OGs on the basis of phylogenetic pattern similarity and chromosomal proximity, we identified 60 co-occurring gene clusters (CGCs). In addition to known genomic islands, including cag pathogenicity island, bacteriophages, and integrating conjugative elements, we identified some novel ones. One island encodes TerY-phosphorylation triad, which includes the eukaryote-type protein kinase/phosphatase gene pair, and components of type VII secretion system. Another one contains a reverse-transcriptase homolog, which may be involved in the defense against phage infection through altruistic suicide. Many of the CGCs contained restriction-modification (RM) genes. Different RM systems sometimes occupied the same (orthologous) locus in the strains. We anticipate that our method will facilitate pan-genome studies in general and help identify novel genomic islands in various bacterial species.

Identification of a Latin American-specific BabA adhesin variant through whole genome sequencing of Helicobacter pylori patient isolates from Nicaragua

Background

Helicobacter pylori (H. pylori) is one of the most common bacterial infections in humans and this infection can lead to gastric ulcers and gastric cancer. H. pylori is one of the most genetically variable human pathogens and the ability of the bacterium to bind to the host epithelium as well as the presence of different virulence factors and genetic variants within these genes have been associated with disease severity. Nicaragua has particularly high gastric cancer incidence and we therefore studied Nicaraguan clinical H. pylori isolates for factors that could contribute to cancer risk.

Methods

The complete genomes of fifty-two Nicaraguan H. pylori isolates were sequenced and assembled de novo, and phylogenetic and virulence factor analyses were performed.

Results

The Nicaraguan isolates showed phylogenetic relationship with West African isolates in whole-genome sequence comparisons and with Western and urban South- and Central American isolates using MLSA (Multi-locus sequence analysis). A majority, 77 % of the isolates carried the cancer-associated virulence gene cagA and also the s1/i1/m1 vacuolating cytotoxin, vacA allele combination, which is linked to increased severity of disease. Specifically, we also found that Nicaraguan isolates have a blood group-binding adhesin (BabA) variant highly similar to previously reported BabA sequences from Latin America, including from isolates belonging to other phylogenetic groups. These BabA sequences were found to be under positive selection at several amino acid positions that differed from the global collection of isolates.

Conclusion

The discovery of a Latin American BabA variant, independent of overall phylogenetic background, suggests hitherto unknown host or environmental factors within the Latin American population giving H. pylori isolates carrying this adhesin variant a selective advantage, which could affect pathogenesis and risk for sequelae through specific adherence properties.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0619-y) contains supplementary material, which is available to authorized users.

Characterisation of worldwide Helicobacter pylori strains reveals genetic conservation and essentiality of serine protease HtrA

HtrA proteases and chaperones exhibit important roles in periplasmic protein quality control and stress responses. The genetic inactivation of htrA has been described for many bacterial pathogens. However, in some cases such as the gastric pathogen Helicobacter pylori, HtrA is secreted where it cleaves the tumour‐suppressor E‐cadherin interfering with gastric disease development, but the generation of htrA mutants is still lacking. Here, we show that the htrA gene locus is highly conserved in worldwide strains. HtrA presence was confirmed in 992 H. pylori isolates in gastric biopsy material from infected patients. Differential RNA‐sequencing (dRNA‐seq) indicated that htrA is encoded in an operon with two subsequent genes, HP1020 and HP1021. Genetic mutagenesis and complementation studies revealed that HP1020 and HP1021, but not htrA, can be mutated. In addition, we demonstrate that suppression of HtrA proteolytic activity with a newly developed inhibitor is sufficient to effectively kill H. pylori, but not other bacteria. We show that Helicobacter  htrA is an essential bifunctional gene with crucial intracellular and extracellular functions. Thus, we describe here the first microbe in which htrA is an indispensable gene, a situation unique in the bacterial kingdom. HtrA can therefore be considered a promising new target for anti‐bacterial therapy.

Complete Genome Sequences of Two Helicobacter pylori Strains from a Canadian Arctic Aboriginal Community

We report here the complete genome sequences of two Amerind Helicobacter pylori strains from Aklavik, Northwest Territories, Canada. One strain contains extra iron-cofactored urease genes and ~140 rearrangements in its chromosome relative to other described strains (typically differing from one another by <10 rearrangements), suggesting that it represents a novel lineage of H. pylori.

Gastric and enterohepatic helicobacters other than Helicobacter pylori

During the past year, research on non-Helicobacter pylori species has intensified. H. valdiviensis was isolated from wild birds, and putative novel species have been isolated from Bengal tigers and Australian marsupials. Various genomes have been sequenced: H. bilis, H. canis, H. macacae, H. fennelliae, H. cetorum, and H. suis. Several studies highlighted the virulence of non-H. pylori species including H. cinaedi in humans and hyperlipidemic mice or H. macacae in geriatric rhesus monkeys with intestinal adenocarcinoma. Not surprisingly, increased attention has been paid to the position of Helicobacter species in the microbiota of children and animal species (mice, chickens, penguins, and migrating birds). A large number of experimental studies have been performed in animal models of Helicobacter induced typhlocolitis, showing that the gastrointestinal microbial community is involved in modulation of host pathways leading to chronic inflammation. Animal models of H. suis, H. heilmannii, and H. felis infection have been used to study the development of severe inflammation-related pathologies, including gastric MALT lymphoma and adenocarcinoma.

HelicoBase: a Helicobacter genomic resource and analysis platform

Background

Helicobacter is a genus of Gram-negative bacteria, possessing a characteristic helical shape that has been associated with a wide spectrum of human diseases. Although much research has been done on Helicobacter and many genomes have been sequenced, currently there is no specialized Helicobacter genomic resource and analysis platform to facilitate analysis of these genomes. With the increasing number of Helicobacter genomes being sequenced, comparative genomic analysis on members of this species will provide further insights on their taxonomy, phylogeny, pathogenicity and other information that may contribute to better management of diseases caused by Helicobacter pathogens.

Description

To facilitate the ongoing research on Helicobacter, a specialized central repository and analysis platform for the Helicobacter research community is needed to host the fast-growing amount of genomic data and facilitate the analysis of these data, particularly comparative analysis. Here we present HelicoBase, a user-friendly Helicobacter resource platform with diverse functionality for the analysis of Helicobacter genomic data for the Helicobacter research communities. HelicoBase hosts a total of 13 species and 166 genome sequences of Helicobacter spp. Genome annotations such as gene/protein sequences, protein function and sub-cellular localisation are also included. Our web implementation supports diverse query types and seamless searching of annotations using an AJAX-based real-time searching system. JBrowse is also incorporated to allow rapid and seamless browsing of Helicobacter genomes and annotations. Advanced bioinformatics analysis tools consisting of standard BLAST for similarity search, VFDB BLAST for sequence similarity search against the Virulence Factor Database (VFDB), Pairwise Genome Comparison (PGC) tool for comparative genomic analysis, and a newly designed Pathogenomics Profiling Tool (PathoProT) for comparative pathogenomic analysis are also included to facilitate the analysis of Helicobacter genomic data.

Conclusions

HelicoBase offers access to a range of genomic resources as well as tools for the analysis of Helicobacter genome data. HelicoBase can be accessed at http://helicobacter.um.edu.my.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-600) contains supplementary material, which is available to authorized users.

A comprehensive analysis of Helicobacter pylori plasticity zones reveals that they are integrating conjugative elements with intermediate integration specificity

BACKGROUND

The human gastric pathogen Helicobacter pylori is a paradigm for chronic bacterial infections. Its persistence in the stomach mucosa is facilitated by several mechanisms of immune evasion and immune modulation, but also by an unusual genetic variability which might account for the capability to adapt to changing environmental conditions during long-term colonization. This variability is reflected by the fact that almost each infected individual is colonized by a genetically unique strain. Strain-specific genes are dispersed throughout the genome, but clusters of genes organized as genomic islands may also collectively be present or absent.

RESULTS

We have comparatively analysed such clusters, which are commonly termed plasticity zones, in a high number of H. pylori strains of varying geographical origin. We show that these regions contain fixed gene sets, rather than being true regions of genome plasticity, but two different types and several subtypes with partly diverging gene content can be distinguished. Their genetic diversity is incongruent with variations in the rest of the genome, suggesting that they are subject to horizontal gene transfer within H. pylori populations. We identified 40 distinct integration sites in 45 genome sequences, with a conserved heptanucleotide motif that seems to be the minimal requirement for integration.

CONCLUSIONS

The significant number of possible integration sites, together with the requirement for a short conserved integration motif and the high level of gene conservation, indicates that these elements are best described as integrating conjugative elements (ICEs) with an intermediate integration site specificity.