INDUCTION AND EVASION OF HOST DEFENSES BY TYPE 1-PILIATED UROPATHOGENIC ESCHERICHIA-COLI

Virtually all uropathogenic strains of Escherichia coli encode filamen tous surface adhesive organelles called type 1 pili. High-resolution e lectron microscopy of infected mouse bladders revealed that type 1 pil us tips interacted directly with the Lumenal surface of the bladder, w hich is embedded with hexagonal arrays of integral membrane glycoprote ins known as uroplakins. Attached pill were shortened and facilitated intimate contact of the bacteria with the uroplakin-coated host cells. Bacterial attachment resulted in exfoliation of host bladder epitheli al cells as part of an innate host defense system. Exfoliation occurre d through a rapid apoptosis-like mechanism involving caspase activatio n and host DNA fragmentation. Bacteria resisted clearance in the face of host defenses within the bladder by invading into the epithelium.