title: Characteristics of Helicobacter pylori variants selected for urease deficiency.
abstract: The urease of Helicobacter pylori is suspected to play a role in the pathogenesis of gastritis. Although all clinical isolates of H. pylori are urease positive (U+), we have selected and characterized several spontaneously arising urease-negative (U-) variants from wild-type strain 60190. Urease-negative variants were identified by growth in medium containing 60 mM urea and arose at a frequency of 10(-5) to 10(-6). The urease activity of the wild-type strain inhibited growth of this strain in the presence of 60 mM urea. U- variants retained the U- phenotype for more than 100 passages on medium with or without urea. The urease activities of the original U+ and derived U- cells were 9.55 to 16.7 and 0.01 to 0.17 U/mg of protein, respectively. Colonial growth and other biochemical characteristics were identical for the strains. U- variants showed three classes of whole-cell sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles: (i) identical to U+; (ii) change in the migration of the 61-kDa urease subunit; and (iii) lack of 61- and 30-kDa subunits. These differences were confirmed by immunoblotting and by protein separation using fast protein liquid chromatography. The U+ strain but not U- variants tolerated exposure to pH 4.0 for 60 min in the presence of urea. Supernatants of the U+ strain and U- variants contained vacuolating cytotoxin activity for HeLa cells in similar titers. By enzyme-linked immunosorbent assay, human serum samples recognized water extract from the U+ strain significantly better than extract from a U- variant lacking urease subunits. In conclusion, this study demonstrates that U- H. pylori variants may arise spontaneously, that urease activity enhances survival at acid pH, and that urease and cytotoxin activities are disparate phenotypes.
authors.affiliation: Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2605.
authors.forename: G I
authors.initials: GI
authors.lastname: Pérez-Pérez
authors.forename: A Z
authors.initials: AZ
authors.lastname: Olivares
authors.forename: T L
authors.initials: TL
authors.lastname: Cover
authors.forename: M J
authors.initials: MJ
authors.lastname: Blaser
mesh_terms: D001426:Bacterial Proteins / Q000302:isolation & purification; D003603:Cytotoxins / Q000633:toxicity; D006367:HeLa Cells; D016480:Helicobacter pylori / Q000201:enzymology* / Q000276:immunology / Q000472:pathogenicity; D006801:Humans; D006863:Hydrogen-Ion Concentration; D014510:Urease / Q000172:deficiency*; D014617:Vacuoles
chemical_list: D001426:Bacterial Proteins; D003603:Cytotoxins; D014510:Urease