Relationship of Helicobacter pylori virulence to gastric pathology in the Western Cape

Relationship ofHelicobacter pylori virulence to gastric pathobiology in the Western Cape. M Kidd. Gastrointestinal Clinic and Department of Medicine, University of Cape Town and Groote Schuur Hospital, Observatory 7925, South Africa. The work presented in this thesis investigated virulence in Helicobacter pylori isolates of the Western Cape and related this virulent fingerprint to alterations in gastric cell physiology and cell cycle events. Initially, the "virulence profile" of 109 isolates from 86 patients with a spectrum of clinically significant gastroduodenal diseases was investigated. The distribution of the vacuolating cytotoxin A (vacA) demonstrated that the low cytotoxic vacA sIb allele was found in all (100%) of the isolates from patients with peptic ulcer disease and gastric adenocarcinoma. The non-cytotoxic vacA s2 allele was found exclusively in patients with gastritis alone and may be an excellent negative marker. Different mid-regions of the gene, which are associated with gastric pathology, were also differentially distributed (m1 with disease and m2 with gastritis alone). These alleles did not, however, segregate absolutely with disease; 40% of patients with gastritis alone were vacA slbml. The gene cagA was identified in all isolates and examination of the 3'-region of this gene revealed alterations, both in length as well as in structure and potential tyrosine phosphorylation sites. This specifically identified one third of patients with gastric cancer (cagA 3'-long), and may be an important marker for disease. The "classically virulent" Type I strains (vacA sl! cagA+) were found in 100% of both peptic ulcer disease and gastric adenocarcinoma isolates. The sensitivity for clinically significant disease of this fingerprint was 100%, but the specificity was, however, only 43%. The structure of the cag pathogenicity island was then examined and deletions in the 5'-region were found more consistently (-60%) in isolates from patients without clinically significant disease. These deletions were associated with the non-cytotoxic vacA s2m2 allele (90%). The two genotypes of the iceA gene were examined and although half of the isolates contained both genes, iceAl was identified more often in isolates from patients with gastric cancer (81 %). Variants of the iceA2 gene, which were shown to have differences in secondary and tertiary protein structure, delineated patients with gastritis alone (iceA2C, 62%) and peptic ulcer disease (iceA2D, 53%). Combination analysis of vacA and iceA status revealed statistically significant associations between disease isolates and vacA slb1iceAl. Nevertheless, one third of isolates from patients with gastritis alone had this virulence-associated genotype. The relationship between the virulence factors and genomic heterogeneity was thereafter examined using repetitive extragenic palindromic and random-amplified polymorphic DNA-PCR. Two clusters were produced for each method. A clustering of isolates from patients with peptic ulcer disease, with the vacA sImI genotype, a short cagA 3'-fragment, and REPllRAPD2 genomic fingerprints were identified. Isolates from patients with gastric adenocarcinoma and gastritis alone ted. l<tVU •• "",