9 - Fimbriae and Pili

Abstract

Pili or fimbriae are proteinaceous, filamentous, polymeric organdies expressed on the surface of bacteria. Pilus has become a generic term used to describe all types of nonflagellar filamentous appendages, and it is used interchangeably with the term “fimbriae.” Pili can act as receptors for bacteriophages, facilitate DNA uptake and transfer (conjugation), and at least one type of pilus, type 4, call function in cellular motility. The primary function of most pili, however, is to act as scaffolding for the presentation of specific adhesive moieties. Adhesive pilus subunits (adhesins) are often incorporated as minor components into the tips of pili, but major structural subunits can also function as adhesins. Adhesins can mediate the interaction of bacteria with each other, with inanimate surfaces, and with tissues and cells in susceptible host organisms. For many bacterial pathogens, adhesive pili play a key role in the colonization of host tissues. Type 1 pill-mediated attachment to bladder epithelial cells is critical in the establishment of urinal tract infections by uropathogenic E. coli. Similarly, binding of P pili to Galα(1–4)Gal sugar moieties in the kidney are necessary for development of pyelonephritis.