The bacterium Helicobacter pylori is the causative agent for peptic ulcer disease. Bacterial adherence to the human gastric epithelial lining is mediated by the fucosylated Lewis b (Leb) histo-blood group antigen. The Leb-binding adhesin, BabA, was purified by receptor activity-directed affinity tagging. The bacterial Leb-binding phenotype was associated with the presence of the cag pathogenicity island among clinical isolates of H. pylori. A vaccine strategy based on the BabA adhesin might serve as a means to target the virulent type I strains of H. pylori.

Helicobacter pylori adherence in the human gastric mucosa involves specific bacterial adhesins and cognate host receptors. Here, we identify sialyl-dimeric-Lewis x glycosphingolipid as a receptor for H. pylori and show that H. pylori infection induced formation of sialyl-Lewis x antigens in gastric epithelium in humans and in a Rhesus monkey. The corresponding sialic acid-binding adhesin (SabA) was isolated with the "retagging" method, and the underlying sabA gene (JHP662/HP0725) was identified. The ability of many H. pylori strains to adhere to sialylated glycoconjugates expressed during chronic inflammation might thus contribute to virulence and the extraordinary chronicity of H. pylori infection.

No abstract

SummaryMost strains of Helicobacter pylori from patients with peptic ulcer disease or intestinal-type gastric cancer carry cagA, a gene that encodes an immunodominant protein of unknown function, whereas many of the strains from asymptomatically infected persons lack this gene. Recent studies showed that the cagA gene lies near the right end of a Ϸ37 kb DNA segment (a pathogenicity island, or PAI) that is unique to cagA þ strains and that the cag PAI was split in half by a transposable element insertion in the reference strain NCTC11638. In complementary experiments reported here, we also found the same cag PAI, and sequenced a 39 kb cosmid clone containing the left 'cagII' half of this PAI. Encoded in cagII were four proteins each with homology to four components of multiprotein complexes of Bordetella pertussis ('Ptl'), Agrobacterium tumefaciens ('Vir'), and conjugative plasmids ('Tra') that help deliver pertussis toxin and T (tumour inducing) and plasmid DNA, respectively, to target eukaryotic or prokaryotic cells, and also homologues of eukaryotic proteins that are involved in cytoskeletal structure. To the left of cagII in this cosmid were genes for homologues of HslU (heat-shock protein) and Era (essential GTPase); to the right of cagII were homologues of genes for a type I restriction endonuclease and ion transport functions. Deletion of the cag PAI had no effect on synthesis of the vacuolating cytotoxin, but this deletion and several cag insertion mutations blocked induction of synthesis of proinflammatory cytokine IL-8 in gastric epithelial cells. Comparisons among H. pylori strains indicated that cag PAI gene content and arrangement are rather well conserved. We also identified two genome rearrangements with end-points in the cag PAI. One, in reference strain NCTC11638, involved IS605, a recently described transposable element (as also found by others). Another rearrangement, in 3 of 10 strains tested (including type strain NCTC11637), separated the normally adjacent cagA and picA genes and did not involve IS605. Our results are discussed in terms of how cagencoded proteins might help trigger the damaging inflammatory responses in the gastric epithelium and possible contributions of DNA rearrangements to genome evolution.

CagA, a major virulence factor of Helicobacter pylori (Hp), is delivered into gastric epithelial cells and exists in phosphorylated and nonphosphorylated forms. The biological activity of the phosphorylated form is well established; however, function(s) of the nonphosphorylated form remain elusive. Here, we report that a conserved motif in the C-terminal region of CagA, which is distinct from the EPIYA motifs used for phosphorylation and which we designate CRPIA (conserved repeat responsible for phosphorylation-independent activity), plays pivotal roles in Hp pathogenesis. The CRPIA motif in nonphosphorylated CagA was involved in interacting with activated Met, the hepatocyte growth factor receptor, leading to the sustained activation of phosphatidylinositol 3-kinase/Akt signaling in response to Hp infection. This in turn led to the activation of beta-catenin and NF-kappaB signaling, which promote proliferation and inflammation, respectively. Thus, nonphosphorylated CagA activity contributes to the epithelial proliferative and proinflammatory responses associated with development of chronic gastritis and gastric cancer.

DNA motifs at several informative loci in more than 500 strains of Helicobacter pylori from five continents were studied by PCR and sequencing to gain insights into the evolution of this gastric pathogen. Five types of deletion, insertion, and substitution motifs were found at the right end of the H. pylori cag pathogenicity island. Of the three most common motifs, type I predominated in Spaniards, native Peruvians, and Guatemalan Ladinos (mixed Amerindian-European ancestry) and also in native Africans and U.S. residents; type II predominated among Japanese and Chinese; and type III predominated in Indians from Calcutta. Sequences in the cagA gene and in vacAm1 type alleles of the vacuolating cytotoxin gene (vacA) of strains from native Peruvians were also more like those from Spaniards than those from Asians. These indications of relatedness of Latin American and Spanish strains, despite the closer genetic relatedness of Amerindian and Asian people themselves, lead us to suggest that H. pylori may have been brought to the New World by European conquerors and colonists about 500 years ago. This thinking, in turn, suggests that H. pylori infection might have become widespread in people quite recently in human evolution.Helicobacter pylori is a microaerophilic bacterium with the extraordinary ability to establish infections in human stomachs that can last for years or decades, despite immune and inflammatory responses and normal turnover of the gastric epithelium and overlying mucin layer in which it resides. It is carried by more than half of all people worldwide and has attracted great attention as a major cause of peptic ulcer disease and an early risk factor for gastric cancer, one of the most frequently lethal of malignancies worldwide (for reviews see references 23, 48, and 60).

The genotypes of 78 strains of Helicobacter pylori from Calcutta, India (55 from ulcer patients and 23 from more-benign infections), were studied, with a focus on putative virulence genes and neutral DNA markers that were likely to be phylogenetically informative. PCR tests indicated that 80 to 90% of Calcutta strains carried the cag pathogenicity island (PAI) and potentially toxigenic vacAs1 alleles of the vacuolating cytotoxin gene (vacA), independent of disease status. This was higher than in the West (where cag PAI ؉ vacAs1 genotypes are disease associated) but lower than in east Asia. The iceA2 gene was weakly disease associated in Calcutta, whereas in the West the alternative but unrelated iceA1 gene at the same locus is weakly disease associated. DNA sequence motifs of vacAm1 (middle region) alleles formed a cluster that was distinct from those of east Asia and the West, whereas the cagA sequences of Calcutta and Western strains were closely related. An internal deletion found in 20% of Calcutta iceA1 genes was not seen in any of ϳ200 strains studied from other geographic regions and thus seemed to be unique to this H. pylori population. Two mobile DNAs that were rare in east Asian strains were also common in Calcutta. About 90% of Calcutta strains were metronidazole resistant. These findings support the idea that H. pylori gene pools differ regionally and emphasize the potential importance of studies of Indian and other non-Western H. pylori populations in developing a global understanding of this gastric pathogen and associated disease.

SummaryGenetic recombination can be important evolutionarily in speeding the adaptation of organisms to new environments and in purging deleterious mutations. Here, we describe polymerase chain reaction (PCR), hybridization and DNA sequence-based evidence of six such exchanges between two strains of Helicobacter pylori during natural mixed infection of a patient in Lithuania. One parent strain contained the 37 kb long, virulence-associated cag pathogenicity island (PAI), and the other strain lacked this PAI. Most H. pylori from the patient had descended from the cag þ parent, but had become cag ¹ during infection. This had resulted from transfer of DNA containing the 'empty site' allele from the cag ¹ strain and homologous recombination, not from excision of the cag PAI without DNA transfer. Other cases of recombination involved genes for an outer membrane protein (omp5 and omp29; also called HP0227 and HP1342) and a putative phosphoenolpyruvate synthase (ppsA ; HP0121). Replacement of a short patch of DNA sequence (36-124 bp) was also seen. As the chance of forming any given recombinant is small, the abundance of recombinants in this patient suggests selection for particular recombinant genotypes during years of chronic infection. We suggest that genetic exchange among unrelated H. pylori strains, as documented here, is important because of the diversity of this gastric pathogen and its human hosts. Certain H. pylori recombinants may grow better in a given host than either parent. The vigour of growth, in turn, could impact on the severity of disease that infection can elicit.