The pathophysiology of infection by uropathogenic Escherichia coli in bladder epithelial cells.20 Uropathogenic E. coli organisms attach to receptors on superficial bladder cells with P fimbriae or type 1 pili. Once contact is established, the bacteria are internalized into the cells, where they can replicate to high levels. However, attachment or invasion can result in the activation of apoptotic pathways within the cells, leading to the eventual exfoliation and clearance of infected host cells. Interactions between E. coli and the cells can also result in the induction of inflammatory cytokines, leading to the influx of polymorphonuclear leukocytes into the bladder epithelium. E. coli can escape from dying cells, thereby avoiding clearance by exfoliation, and infect surrounding and underlying epithelial cells. Within the bladder epithelium, E. coli can escape immune surveillance and persist at subclinical levels. (IL-6 — interleukin-6; IL-8 — interleukin-8)