Overview
Clinical Meaning
Urinary tract infections result from microbial invasion of the normally sterile urinary tract.
Urinary tract infections result from microbial invasion of the normally sterile urinary tract. The most common pathogen is uropathogenic Escherichia coli (UPEC), accounting for 75-95% of uncomplicated UTIs. UPEC possesses virulence factors including type 1 fimbriae (FimH adhesin) that bind to uroplakin receptors on urothelial cells, P fimbriae that bind to globoseries glycolipids on renal epithelium facilitating ascending infection, and iron acquisition systems (siderophores) that enable survival in iron-limited urine. After adhesion, bacteria invade superficial umbrella cells and form intracellular bacterial communities (IBCs) that are protected from immune clearance and antibiotics. The host immune response involves Toll-like receptor 4 (TLR4) recognition of lipopolysaccharide, triggering NF-kB-mediated release of IL-6, IL-8, and IL-1beta, which recruit neutrophils into the urinary tract producing pyuria. Urothelial exfoliation serves as a defense mechanism to shed infected cells but also exposes deeper transitional epithelium to bacterial invasion. In complicated UTI, structural or functional abnormalities (obstruction, reflux, neurogenic bladder, indwelling catheters) impair normal washout mechanisms and create biofilm environments that resist both immune clearance and antibiotic penetration. Catheter-associated UTI (CAUTI) involves biofilm formation on catheter surfaces where organisms...