LACK OF EVIDENCE FOR SIALIDASE ACTIVITY IN HELICOBACTER-PYLORI

The role of sialic acid for the adhesion of Helicobacter pylori to gas tric mucosa cells and/or to the mucin layer is still under debate. Sev eral but not all H. pylori strains express a sialic acid-binding adhes in, specific for terminal alpha-2,3-sialic acid residues. Recently, th e production of sialidase by H. pylori was reported [Dwarakanath, A.D. et al. (1995) FEMS Immunol. Med. Microbiol. 12, 213-216]; We analysed several strains isolated from gastric biopsies cultivated both in liq uid media and on agar plates for sialidase. Activity of this enzyme wa s first assayed using the fluorigenic substrate 4-methylumbelliferyl-a lpha-D-N-acetylneuraminic acid. Since the fluorimetric assay can give false-positive results caused by non-specific interactions with umbell iferyl-tagged substances, we used also the more sensitive and specific assay with sialyl-[H-3]lactitol as a substrate. No evidence for siali dase activity of H. pylori strains, cultivated under both inducible an d non-inducible conditions, was obtained.