ROLE OF THE BORDETELLA-PERTUSSIS MINOR FIMBRIAL SUBUNIT, FIMD, IN COLONIZATION OF THE MOUSE RESPIRATORY-TRACT

Bordetella pertussis fimbriae are composed of a major subunit, Fim2. o r Fim3, and the minor subunit FimD. Using immunoelectron microscopy, w e provide evidence that FimD is located at the fimbrial tip. The role of FimD in colonization of the mouse respiratory tract was studied by using two fimbrial mutants:. a mutant completely devoid of fimbriae (d esignated FimD(-)) and a mutant devoid of the major fimbrial subunits but still producing the minor subunit (designated FimD(+)). The abilit y of the two fimbrial mutants to colonize the nasopharynx, trachea, an d lungs was compared with those of the wild type parental strain and a filamentous hemagglutinin (FHA) mutant, Of the three mutants studied, the FimD(-) mutant showed the greatest defect, colonizing less well i n the nasopharynx, trachea, and lungs. The most pronounced defect in c olonizing ability of the three mutants was observed in the trachea. Ho wever, the colonizing defect of the FNA and FimD mutants in the trache a was observed only during the first 3 days of infection. After 10 day s, the colonization level was nearly restored to wild-type levels. The FHA and FimD(+) mutants showed a slight colonization defect in the na sopharynx but no defect in the lungs. A maltose binding protein-FimD f usion protein and a peptide derived from FimD were able to bind to hep arin, a member of a class of sulfated sugars which are ubiquitous in t he respiratory tract. Recently it was shown (W. L. W. Hazenbos, C. A. W. Geuijen, B. M., van den Berg, F. R. Mooi, and R. van Furth, J. Infe ct. Dis. 171:924-929, 1995) that FimD also binds to the integrin VLA-5 , and our results suggest that the binding of B. pertussis to these tw o molecules plays an important role in colonization of the respiratory tract of the mouse.