The pathogenic role of fimbriae of Haemophilus influenzae type b in murinebacteraemia and meningitis

Complement activation and development of murine bacteraemia and meningitis following intranasal instillation of cell-bound fimbriated or non-fimbriate d organisms were compared to clarify the role of fimbriae in the pathogenes is of illnesses caused by Haemophilus influenza type b (Hib). In-vitro resi stance of non-fimbriate bacteria to the bactericidal effects of normal huma n serum was at least 400 times greater than that of fimbriate bacteria. The amount of C3 bound to fimbriate Hib was more than that to non-fimbriate Hi b. When mice were infected with fimbriate bacteria, 11.5% died. When mice w ere infected with non-fimbriate bacteria, the mean number of viable organis ms gradually increased or was constant up to day 7; 38.5% of these mice die d, These in vivo results were coincident with the in-vitro data. However, t he content of polyribosyl ribitol phosphate (PRP) in fimbriate organisms wa s the same as in non-fimbriate organisms. These results indicate that fimbr iate Hib may be less likely to produce bacteraemia and meningitis, correlat ing,vith the greater susceptibility to complement-mediated bacteriolysis an d the lower mortality seen,vith this type of organism, although fimbriae in crease adherence to epithelial cells (mucosal surface).