A comparison of the adherence of fimbriated and nonfimbriated Haemophilus influenzae type b to human adenoids in organ culture.

Adherence of fimbriated and nonfimbriated variants of a single strain of Haemophilus influenzae type b to organ cultures of human adenoidal tissue was measured by three assays, two of which were quantitative. In one assay, the adherence of radioactively labeled bacteria was measured; the numbers of CFU of bacteria per gram of adenoidal tissue were 16.0 +/- 6.7 for fimbriated bacteria and 10.2 +/- 4.0 for nonfimbriated bacteria (P less than 0.05). In the second assay, adherent CFU were determined directly; the results were 23.4 +/- 17.2 CFU/g of tissue for fimbriated bacteria and 5.1 +/- 2.2 CFU/g for the nonfimbriated variant (P less than 0.02). By combining data from the two assays it appears that fimbriated and nonfimbriated bacteria do not compete for the same site on the tissue, and that the adherent bacteria do not change their state of fimbriation under the assay conditions used. In contrast, the third assay, scanning electron microscopy, showed very poor adherence of nonfimbriated bacteria. Fimbriated bacteria, on the other hand, adhered in clusters to nonciliated epithelial cells. Overall, the data indicate that fimbriae enhance adherence of H. influenzae type b to a type of tissue that is a normal site of human colonization and that nonfimbriated bacteria adhere by a distinctly different mechanism.