GENETIC-RELATIONSHIP AMONG ISOLATES OF HELICOBACTER-PYLORI - EVIDENCEFOR THE EXISTENCE OF A HELICOBACTER-PYLORI SPECIES-COMPLEX

We investigated the population genetics of 23 isolates of H. pylori by allozyme electrophoresis using 16 enzyme loci. Isolates were obtained from adult patients of whom 48% were of Greek extraction. Eight patie nts (35%) had an active duodenal ulcer. Allelic variation per loci ran ged from 2 to 11 alleles. Four major genetic clusters were apparent, h aving > 75% fixed genetic differences. There was no distinct clusterin g (clonal structure) on the basis of the geographical origin of the pe rsons from whom isolates were obtained, indicating that this bacterium has not recently jumped a species barrier into humans, Isolates assoc iated with ulcer disease were not monophyletic, with isolates from ulc er patients being found in phylogenetically diverse branches of the de ndogram derived from the data. Based on the genetic diversity of H. py lori isolates, we propose that isolates should be classified as belong ing not to a single species but to a 'Helicobacter pylori species-comp lex'.