Phenotypic diversity in Lewis expression of Helicobacter pylori isolates from the same host

Populations of Helicobacter pylori cells show a stable expression of Lewis, surface antigens, although phase variation may occur among individual orga nisms grown in vitro. We searched for variation in Lewis phenotypes among H , pylori cells of minimally in vitro-passaged isolates. Lewis expression in 180 clonal H, pylori populations from the primary culture of 20 gastric bi opsy samples from 12 patients, and that in 160 isolates from primary cultur es from 16 experimentally infected rodents, were examined by enzyme immunoa ssays. Substantial differences in Lewis expression were found among the iso lates from 9 (75%) of 12 patients, These differences were unrelated to over all genetic diversity as determined by polymerase chain reactions for rando m amplified polymorphic DNA or cagA status, and they persisted during subse quent in vitro passage. In contrast, Lewis expression was highly uniform in H, pylori isolates from different rodents infected for up to 20 weeks. Var iation in H, pylori Lewis expression in genetically closely related organis ms in human subjects may provide a pool of bacterial phenotypes for the con tinuous selection of optimally host-adapted populations suitable for persis tence.