Analysis of Genetic Diversity in Cytotoxin-Producing and Non-Cytotoxin Producing Helicobacter pylori Strains

Analysis of 32 Helicobacter pylori strains indicated a strong association between the presence of the cagA gene and a specific type of vaeA allele found predominantly in cytotoxin-producing strains (P < .(01). To determine whether tox+/CagA+ and tox−/CagA strains constituted two separate noncombining lineages, sequences of the H. pylori ureC gene, cysS homologue, and the intergenic region between cysS and vaeA were determined for multiple strains. Themean levels of nucleotideidentity in the three regions were 96.7% ± 0.5%,95.0% ± 1.0%,and 89.0% ± 2.9%, respectively. Multiple sequence alignments and dendrograms based on these three regions failed to identify two clonal populations of organisms for which cagA and vaeA genotypes were markers. The presence of a 63- to 64-bp insertion in the cysS-vaeA intergenic region was unrelated to the vacA genotype of the strains. These data suggest that recombination between Helieobaeter genomes may occur in vivo.