HIGH-LEVEL GENETIC DIVERSITY IN THE VAPD CHROMOSOMAL REGION OF HELICOBACTER-PYLORI

Helicobacter pylori isolates from different patients are characterized By diversity in the nucleotide sequences of individual genes, variati on in genome size, and variation in gene order, Genetic diversity is p articularly striking in vacuolating cytotoxin (vacA) alleles, In this study, five open reading frames (ORFs) were identified within a 4,2-kb region downstream from vacA in H. pylori 60190, One of these ORFs was closely related to the virulence-associated protein D (vapD) gene of Dichelobacter nodosus (64.9% nucleotide identity), A probe derived fro m vapD of H. pylori 60190 hybridized with only 19 (61.3%) of 31 H. pyl ori strains tested, Sequence analysis of the vapD region in vapD-negat ive H. pylori strains revealed that there were two different families of similar to 0.5-kb DNA segments, which were both unrelated to vapD. The presence of vapD was not associated with any specific family of va cA alleles, These findings are consistent with a recombinational popul ation structure for H. pylori.