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ABSTRACTHemolysins have been found to possess a variety of functions in bacteria, including a role in virulence. Helicobacter pyloridemonstrates hemolytic activity when cultured on unlysed blood agar plates which is increased under iron-limiting conditions. However, the role of an H. pylorihemolysin in virulence is unclear. Scrutiny of the H. pylori26695 genome sequence suggests the presence of at least two distinct hemolysins, HP1086 and HP1490, in this strain. Previous studies have shown that the in vitro hemolytic activity of H. pyloriis reduced when it is coincubated with dextran 5000, suggesting the presence of a pore-forming cytolysin. HP1086 has homology to pore-forming cytolysins (TlyA) from other bacterial species, and the introduction of the clonedH. pylori tlyAgene into a nonhemolyticEscherichia colistrain conferred hemolytic activity. AnH. pylori tlyAdefined mutant showed reduced in vitro hemolytic activity, which appears to be due to pore formation, as the hemolytic activity of the wild-type strain is reduced to the same level as the tlyAmutant by the addition of dextran 5000. The mutant also showed reduced adhesion to human gastric adenocarcinoma cells and failed to colonize the gastric mucosa of mice. These data clearly suggest a role in virulence for H. pyloriTlyA, contrary to the suggestion that hemolytic activity is an in vitro phenomenon for this pathogen.

Expression of the two Helicobacter pyloriflagellin proteins FlaA and FlaB is required for full motility and persistent infection of the gastric mucosa. The mechanisms and regulation of the biosynthesis and export of flagella in H. pyloriare still poorly understood. Scrutiny of the H. pylori26695 genome sequence revealed homologues of FliQ and FlhB. The roles of the fliQand flhBgenes in H. pyloriwere investigated by the construction and characterisation of defined isogenic mutants. The results indicate that these genes are involved in the flagellar expression, adhesion to and colonisation of the gastric mucosa.