Fimbriae (pili): molecular basis of Pseudomonas aeruginosa adherence

Pseudomonas aeruginosa produces polar pili which promote the adherence of the organism to host mucosal surfaces and to blood-borne phagocytic cells such as polymorphonuclear leukocytes. Pseudomonas polar pili are flexible filaments of 52 A diameter and 2500 nm average length. They consist of a single type of protein subunit, pilin, of molecular weight 15,000, which is arranged in a helical mode of 5 subunits per turn and a pitch of 41 A. Purified whole pili, and anti-pilus antiserum both inhibited the interaction of Pseudomonas aeruginosa strains with human buccal epithelial cells and PMNs, suggesting that Pseudomonas adherence to these mammalian cells is pilus mediated. No correlation was found between the level of cell surface fibronectin on human buccal endothelial cells and the adherence of Pseudomonas bacteria. Pseudomonas adherence to buccal endothelial cells obtained from patients with cystic fibrosis was somewhat less than that to buccal endothelial cells obtained from healthy individuals. Fibronectin levels on buccal endothelial cells from patients with cystic fibrosis were not significantly different than those found on buccal endothelial cells from healthy individuals. Studies with peptide fragments derived from purified pili showed that only one peptide encompassing 23 amino acid residues at the C-terminus of the pilus protein was able to inhibit in vitro adherence of P. aeruginosa PAK to human buccal cells. This peptide domain was tentatively assigned the receptor-binding function.