Quasispecies development in heucomcter pylori

Introduction. H. pylori isolates show a high level of genomic diversity, but the basis for this phenomenon is unknown We hypothesized that genomic mutation and adaptation may appear within an H. pylori strain during its persistence in an individual host. Methods H. pylori isolates were obtained from (3 patients with non-ulcer dyspepsia at baseline and after a 7-10 year follow-up. DNA was studied by PCR for cagA, vacA. weA and IS605, by RAPD PCR, and by AFLP analysis. IS605 and recA PCR products were sequenced and IS<505-positive isolates were tested by Southern hybridization with an ]S605 probe Lewis-x and -y phenotypes were determined by ELISA Results. Genotyping revealed that baseline and follow-up isolates represented different strains in 2 (15%) of 13 patients, but the same strain in the other 11 patients, 100% identity was demonstrated within 10 of these 11 pairs for a 246 bp recA PCR product, each pair having a different sequence. In one pair, also with a unique sequence, subpopulations with one basepair difference were observed both in the baseline and follow-up isolate. Despite the evidence that each of these 11 pairs represented a single strain, there were distinct and reproducible dissimilarities shown within each pair by RAPD PCR as well as by AFLP analyses. Lewis-x phenotypes did not change during fol tow-up, but the expression of Lewis-y decreased significantly. Conclusion: The genetic changes detected by RAPD PCR and AFLP indicate that genetic drift occurs within H. pylon strains over the course of years of colonization of a single host. This indicates the development of quasispecies within H. pylori.