Heterogeneity of cag genotypes and clinical outcome of Helicobacter pylori infection.

Helicobacter pylori infecting strains may include colony subtypes with different cytotoxin-associated gene (cag) genotypes. We sought to determine whether the cag heterogeneity of infecting strains is related to the clinical outcome of infection. Gastric biopsies for culture and histologic study were taken from 19 patients infected with cagA-positive strains (6 with duodenal ulcer, 8 with atrophic gastritis, and 5 with nonatrophic gastritis). For each biopsy, DNA was extracted from 10 single colonies and from a sweep of colonies. Polymerase chain reaction (PCR) for cagA and cagE (both located in the right half of cag) and virB11 (located in the left half of cag) was performed. Random amplified polymorphic DNA PCR (RAPD-PCR) and sequencing of glmM PCR product were performed to verify strain identity of colonies with different cag genotypes. In all patients, PCR from sweeps were positive for cagA, showing that all specimens contained cagA-positive H. pylori subtypes. In 11 patients, PCR products from all colonies were positive for cagA, cagE, and virB11, but in 8 patients, PCR products from varying numbers of colonies were negative for 1 or more cag genes. RAPD-PCR and sequencing of glmM PCR product confirmed the strain identities of colonies with different cag genotypes. We detected cag deletions in 6 of 8, 2 of 5, and 0 of 6 patients with atrophic gastritis, nonatrophic gastritis, and duodenal ulcer, respectively (P = .02). In conclusion, changes in cag genotype in single colony isolates from subjects infected with cagA-positive H. pylori strains are more common in atrophic than in nonatrophic gastritis or duodenal ulcer. These findings are consistent with host-induced (acid secretion?) adaptive changes in cag genotype during infection.

Heterogeneity of cag genotypes in Helicobacter pylori isolates from human biopsy specimens.

The Helicobacter pylori chromosomal cluster of genes known as the cytotoxin-associated gene (cag) island may have different compositions in infecting strains. In this study, we analyzed 150 single colonies obtained from gastric biopsy specimens from 10 patients infected with cagA-positive H. pylori strains and sweep isolates (isolates harvested with sweep in different points of the plate) from 6 patients infected with cagA-negative strains. Three loci in the cag island (cagA, cagE, and virB11) and the conserved gene glmM (ureC) were investigated by PCR. The levels of anti-H. pylori and anti-CagA antibodies in patient sera were also measured. For subjects infected with cagA-negative strains, all sweep isolates were also negative for cagE and virB11, suggesting the complete absence of the cag island. For subjects infected with cagA-positive strains, most of the isolates were positive for all three genes studied, whereas 24.7% of the isolates had a partial or total deletion of the cag island. cagA, cagE, and virB11 were, respectively, present in 87.3, 77.3, and 90% of the colonies. The deletion of virB11 was always associated with the deletion of cagA and/or cagE. H. pylori colonies with different cag genotypes were isolated within a single gastric biopsy specimen from 3 of the 10 patients and were further characterized by random amplified polymorphic DNA (RAPD) analysis and by sequencing of an arbitrarily selected gene segment. Although the colonies had different cag genotypes, their RAPD profiles were highly similar within each patient, and the nucleotide sequences of the selected gene segment were identical. All of the patients had detectable antibodies against H. pylori, and 9 of 10 had anti-CagA antibodies. In conclusion, we show that a single infecting H. pylori strain may include variable proportions of colony subtypes with different cag genotypes. The extension of our analysis to patients with well-characterized gastric diseases may provide significant information on the relationship between cag genotypes and clinical outcomes of H. pylori infections.