Background & aims: Duodenal ulcer formation in persons infected with Helicobacter pylori correlates with the expression of the cytotoxin-associated gene A (cagA) and the vacuolating cytotoxin (VacA). The aim of this study was to assess the occurrence of cagA and VacA variants among H. pylori isolates.
Methods: H. pylori was isolated from 8 members of one family with a history of peptic ulcer disease (PUD). Each strain was characterized by random amplified polymorphic DNA (RAPD) fingerprinting. cagA was detected by polymerase chain reaction (PCR), Southern blotting, and colony hybridization. Viable H. pylori was added to mammalian cells to assess their cytotoxin activity.
Results: The RAPD patterns of the 8 patients' strains were similar. Analysis of 10 single colonies from the primary culture plates showed that all but 1 subject harbored multiple H. pylori subtypes. The proportion of cagA-positive colonies on the primary culture plates ranged from 0% to 90% between the isolates from all patients. In addition, the different H. pylori subtypes showed no cytotoxin activity in mammalian cells.
Conclusions: Genotypic comparison of H. pylori isolated from different patients requires analysis of multiple colonies selected from the primary culture plate. In addition, infection by cagA-positive H. pylori in the family members with PUD (subjects 2-8) is consistent with the observed association between cagA positivity and PUD.