Structure and function of Escherichia coli type 1 pili: new insight into the pathogenesis of urinary tract infections.

The initial step in the establishment of a mucosal bacterial infection is the interaction of bacterial adhesive proteins with epithelial cells, an event that is often followed by invasion of the epithelial cell. Invasion of host cells has been proposed to provide bacterial pathogens with a means of escaping the harsh extracellular environment, where antibodies, complement, defensins, and other antibacterial molecules are abundant. Bacterial invasion can also facilitate the spread of microbes across and within tissue barriers, allowing for the dissemination of the infection. Uropathogenic Escherichia coli (UPEC), the primary causative agent of urinary tract infections (UTIs), has been presumed to be a predominantly extracellular pathogen. This concept has been challenged by recent studies demonstrating the ability of UPEC to invade bladder epithelial cells [1–3]. Two adhesive organelles associated with UPEC, the Dr adhesins and type 1 pili, have been linked to epithelial invasion by UPEC. This review will focus on the structure and assembly of type 1 pili and the mechanisms and consequences of type 1 pilus–mediated invasion of bladder epithelial cells.