Characteristics of the phagocytic cup induced by uropathogenic Escherichia coli

Uropathogenic Escherichia coli invade the urothelial umbrella cells by using the zipper mechanism. However, the details of the early events of this invasion, such as the formation of the phagocytic cup, are not yet well understood. We show here, using thin section electron microscopy and immunogold labeling, that the plasma membrane curves around the bacterial surface in the phagocytic cup. There exists a uniform gap between the bacterium and the urothelial membrane, and actin filaments are present in the phagocytic cup. We suggest that the action-reaction between the mechanical forces generated by pilus retraction of them bacterium and the actin polymerization in the urothelial cell plays a role in maintaining the phagocytic cup.