CHARACTERIZATION OF MECHANISMS INVOLVED IN ADHERENCE OF HAEMOPHILUS-DUCREYI TO EUKARYOTIC CELLS

The adherence of Haemophilus ducreyi to eukaryotic cells of various or igins was investigated by means of a microassay using radiolabelled ba cteria. The influence of physicochemical conditions and of different i nhibitors on adherence to HEp-2 cells and human fibroblasts was examin ed. H. ducreyi strains manifested substantial adherence capacity (rang e, 11-38% of inoculum) to different cells, not discriminating between human and animal origin. The level of adherence was temperature-depend ent, being substantially decreased by incubation at 4 degrees C, but w as unaffected in the pH range 4-10. The adherence level was significan tly reduced in the presence of sodium chloride or tetramethylurea (a h ydrophobic bond-breaking agent). In addition, H. ducreyi bacteria mani fested a pronounced capacity for binding Congo red to the surface, in comparison with the low binding ability of H. influenzae type b. This further indicates hydrophobic domains to be accessible on the surface of H. ducreyi. Inhibition studies with bacterial EDTA extract, sialic acid, heparin and heparan sulphate resulted in a significant reduction in adherent bacteria. However, adherence was not inhibited with crude 24 kDa pili material, LOS of H. ducreyi or fibronectin. Neither crude nor purified 24 kDa protein of H. ducreyi bacteria showed any capacit y to bind monolayers of HEp-2, HeLa or human fibroblasts cells, as tes ted by immunoblot using specific polyclonal antibodies. The overall re sults suggest that adherence of H. ducreyi to eukaryotic cells is not specific to a particular cell type, human or animal. Adherence to HEp- 2 cells involves a multiplicity of factors such as ionic and hydrophob ic forces, and can be mediated by tissue heparin/heparan sulfate prote oglycans. However, specific binding to HEp-2 cells does not seem to be mediated by the 24 kDa pill protein of H. ducreyi.