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-producingstrains (P <.(01). To determine whether tox"/CagA+ and tox-/CagA strains constitutedtwo separate noncombining lineages, sequences of the H. pylori ureC gene, eysS homologue, and the intergenic region between eysS and vaeA were determined for multiple strains. The mean levels of nucleotideidentity in the three regions were 96.7 %:::t 0.5%,95.0 %:::t 1.0%,and 89.0 %:::t 2.9%, respectively. Multiple sequence alignments and dendrograms based on these three regions failed to identify two clonal populations of organisms for which eagA and vaeA genotypes were markers. The presence of a 63- to 64-bp insertion in the eysS-vaeA intergenic region was unrelated to the vacA genotype of the strains. These data suggest that recombination between Helieobaeter genomes may occur in vivo. Helicobacter pylori is the cause of chronic superficial gastri-tis in humans and a major etiologic agent in the development of peptic ulcer disease and possibly gastric cancer [1]. Studies of H. pylori isolates by a number of methods [2-5] suggest that there is a high level of genetic diversity among strains. However, diversity within individual H pylori genes has no