Cell envelope characteristics of Helicobacter pylori: their role in adherence to mucosal surfaces and virulence

Abstract

Helicobacter pylori colonises the gastric mucosa of humans and causes both antral gastritis and duodenal ulcer disease. Exactly how H. pylori causes disease is not known but several pathogenic determinants have been proposed for the organism. These include adhesins, cytotoxins and a range of different enzymes including urease, catalase and superoxide dismutase. Surface molecules of H. pylori such as flagella, lipopolysaccharide, the urease enzyme and outer membrane proteins are putative adhesin molecules. While phosphatidylethanolamine and the Lewis(b) blood group antigen have been proposed as receptor molecules for the organism the exact mechanism by which H. pylori adheres to the gastric mucosa has still to be identified. Characterisation of the adhesins of H. pylori could lead to the development of adhesin analogues for use in the inhibition of colonisation and improved therapy for ulcer disease. In vivo studies with isogenic mutants which are incapable of adhering to the gastric mucosa would greatly clarify the significance of adherence. Such mutants could possibly be useful as a vaccine against infection with wild-type organisms.

Ultrastructural characterization of Anaerobiospirillum succiniciproducens and its differentiation from Campylobacter species

“…Helicobacter pylori is also characterized by lophotriche £agellation [9], but in contrast to A. succiniciproducens the number of £agella is lower (2^9 £agella). Furthermore, each £agellum of H. pylori is enveloped by a membraneous sheath [10]. Examinations using the fast negative-staining technique revealed a clear di¡erence to other cork-screw species such as the Campylobacter species with monotriche £agellation, or the Treponema species with periplasmic £agella.…”

Identification of an immunogenic 18-kDa protein of Helicobacter pylori by alkaline phosphatase gene fusions

“…These include the vacuolating cytotoxin (VacA), a secreted 87-kDa protein present in a subset of H. pylori strains associated with the more serious clinical outcomes of H. pylori infection [23]. Various other secreted or surface-located proteins involved in motility [24], adhesion [25] and iron uptake [26] have been identi®ed also. Progress in identifying secreted or membrane proteins by standard biochemical techniques has been hampered by the presence of the highly immunogenic urease and GroEL homologue proteins.…”

Exploring novel vaccines against Helicobacter pylori: protective and therapeutic immunization

“…2). Among the pathogenic determinants present in all the bacterial strains are a range of different enzymes, including urease, catalase and superoxide‐dismutase; the flagella; and a number of adhesins (adherin proteins) that promote tissue specific colonization (18, 19). Survival of H. pylori in the acidic environment of the stomach is probably due to its ability to establish a positive inner membrane potential and subsequently to modify its microenvironmental pH through the action of urease and the release of factors that inhibit acid production by parietal cells.…”

“…Colonization factors identified in H. pylori to date include (i) bacterial urease (18); (ii) flagella (19); and (iii) adhesion molecules (51, 52).…”

“…In the gnotobiotic‐piglet model, the urease has been shown to be essential for colonization, and urease negative mutants obtained by gene disruption fail to colonize. Furthermore, urease neutralizes the acidic microenvironment and elevate the pH of the gastric fluid, thus enabling the organism to survive (18, 55). In addition, the ammonia released by the action of the urease may contribute to damage of the gastric epithelium.…”