CHARACTERIZATION OF BARTONELLA-BACILLIFORMIS FLAGELLA AND EFFECT OF ANTIFLAGELLIN ANTIBODIES ON INVASION OF HUMAN ERYTHROCYTES

Bartonella bacilliformis is the etiologic agent of Oroya fever in huma ns. Flagellum-mediated motility has been postulated as a major virulen ce factor for invasion of host cells. To address this hypothesis, we p urified and characterized flagella from strain KC584 and then assessed their role in human erythrocyte association and invasion. Electron mi croscopy of the flagellar preparation showed a high concentration of f ilaments with a mean wavelength of 800 nm. Sodium dodecyl sulfate-poly acrylamide gel electrophoresis, immunoblot analysis, and KBr density g radient centrifugation indicated that the flagellar filament is compos ed of a polypeptide of 42 kDa. The flagellin is partially (ca. 50%) re sistant to treatment with trypsin. The first 17 amino acid residues of the N terminus of the mature flagellin protein are GAAILTNDNAMDALQDL and show approximately 46% sequence identity to the residues of the N termini of two Caulobacter crescentus flagellin proteins. A monospecif ic polyclonal antibody to the flagellin protein was generated, and its specificity was verified by both immunoblot and immunogold analyses. Human erythrocyte invasion assays performed with bartonellae exposed t o the antiflagellin antiserum showed a significant decrease in bacteri al association with and invasion of human erythrocytes in comparison w ith that in bartonellae exposed to preimmune rabbit serum or phosphate -buffered saline (PBS) controls. These results suggest that flagella a re an important component in the invasiveness of B. bacilliformis.