Variable adherence of fimbriated Haemophilus influenzae type b to human cells

Abstract

The attachment of isogenic fimbriated and nonfimbriated Haemophilus influenzae type b variants to human cells was studied by using a radioactive assay and an indirect immunofluorescent assay. As described previously, fimbriated H. influenzae variants adhered to a greater extent than nonfimbriated variants to human buccal epithelial cells (2.1 and 0.29 bacteria per cell, respectively, as determined by the radioactive assay (P < 0.05]; 7.6 and 1.6 bacteria per cell, respectively, as determined by the immunofluorescent assay (P < 0.01]). As the concentration of fimbriated bacteria was increased, so were the numbers of adherent bacteria; in contrast, increasing the bacterial concentration had a much smaller effect on adherence of nonfimbriated H. influenzae type b. The distribution of bacteria on the buccal cells also differed. Whereas 37% of the buccal cells failed to bind nonfimbriated H. influenzae type b, failure to bind was observed for only 4% of the buccal cells exposed to fimbriated H. influenzae. In contrast, adherence to human foreskin fibroblasts was low regardless of the presence of fimbriae. On the other hand, fimbriated H. influenzae type b adhered less well than nonfimbriated variants to HEp-2 cells (1.6 and 3.8 bacteria per cell, respectively, as determined by the radioactive assay [P < 0.05]; 1.3 and 4.8 bacteria per cell, respectively, as determined by the immunofluorescent assay [P < 0.02]). Whereas adherence to HEp-2 cells increased considerably as the concentration of nonfimbriated bacteria was increased, there was only a small enhancement of adherence with an increase in the concentration of fimbriated H. influenzae type b. Furthermore, only 16% of the HEp-2 cells failed to bind nonfimbriated H. influenzae type b, whereas 50% failed to bind fimbriated H. influenzae type b. These data indicate that H. influenzae type b may contain two adhesins. One is associated with fimbriae and enables adherence to buccal cells, whereas the other is nonfimbrial and is associated with adherence to HEp-2 cells. It is not known whether either of these adhesins plays a role in pathogenesis.

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

“…Since adherence by both F+ and F-bacteria is complete by 2 |j _ A S> _ _ s a ; : t t ' sm ore than 95% of the bacteria remaining in the medium, it is unlikely that this apparent lack of competition is due to a large excess of receptor sites on the tissue. Apparently F+ and F-H. influenzae each recognize different receptors in the adenoidal tissue, a finding that is supported by other work in our laboratory, demonstrating preferred adherence of F+ bacteria to human buccal epithelial cells in contrast to preferred adherence of F-bacteria to HEp-2 cells (17).…”

“…There is, however, evidence that fimbriae are not the sole adhesin of H. influenzae type b. Nonfimbriated variants adhere better than fimbriated forms to HEp-2 cells, a tissue culture cell line derived from human epithelium (17). Also fresh nonpassaged cultures of human nasopharyngeal isolates from children with systemic H. influenzae type b infections consist predominately of nonfimbriated forms (12).…”

Loss of capsule expression by Haemophilus influenzae type b results in enhanced adherence to and invasion of human cells

“…Using the human nasopharyngeal organ culture model, Farley et al (8) and Loeb et al (18) noted that nonpiliated strains were capable of mucosal attachment. In a comparison of piliated and nonpiliated forms of H. influenzae C54, Sable and coworkers found that adherence to HEp-2 cells was greater by nonpiliated organisms (26). Our results provide further support for nonpilus mechanisms of interaction with human epithelial cells and indicate an important influence of the capsule.…”

Blocking of fimbria-mediated adherence of Haemophilus influenzae by sialyl gangliosides

“…Adherence to respiratory epithelium is generally assumed to be the first step in carriage and the pathogenesis of diseases by encapsulated and nonencapsulated Haemophilus influenzae (2,25). Fimbriae of nonencapsulated as well as of type b H. influenzae mediate the binding of bacteria to oropharyngeal epithelial cells and to erythrocytes (3,6,12,13,15,18,23,27). In vitro binding of H. influenzae was shown to be restricted to those cells of human tissues involved in H. influenzae infections (21).…”