ABSTRACT
Type 4 fimbriae (or pili) occur in a wide variety of Gram-negative bacterial pathogens including Neisseria gonorrhoeae, Pseudomonas aeruginosa, Moraxella bovis, and Dichelobacter nodosus. The commercial development of multivalent vaccines containing fimbriae representing all serogroups of pathogenic D. nodosus, N. gonorrhoeae, or M. bovis is impractical due to the specialized culture conditions of these organisms and their reluctance to readily produce fimbriae in liquid media. The exact function(s) and biological role(s) of type 4 fimbriae are not yet clearly defined. They appear to mediate adhesion to epithelial cells and to mediate twitching motility, as well as to be (directly or indirectly) linked to agar corrosion, DNA uptake, and sensitivity to certain bacteriophages. The genetic topography of the region adjacent to the fimbrial subunit gene has now been described in a number of species, all of which are different. Upstream of pilA, and in the opposite transcriptional orientation, are three genes (pilB, C, and D) that are required for fimbrial biogenesis.
