UPEC coat their surfaces with type 1 pili, rigid fibers which contain a distal mannose-binding adhesin. Upon entry into the urinary tract, this adhesin (FimH) recognizes and binds to specific mannosylated glycoproteins called uroplakins that coat the bladder surface. This binding event initiates complicated signaling cascades in both the bacterium and the host, with the immediate result of invasion of the bacterium into the epithelial cell via a zipper-like mechanism.
Once inside the bladder epithelial cells, UPEC grow and multiply to form intracellular bacterial communities. These communities mature into biofilms, completely enclosed within individual bladder superficial cells. Intracellular biofilms engorge the epithelial cell which then extends into the bladder lumen to give the appearance of a pod.
Bacteria on the edge of the intracellular biofilm begin to detach from the community and escape from the cell into the bladder lumen. This escape, termed fluxing, results in numerous extracellular bacteria, often in a filamentous state, that bind to adjacent cells and initiate a second round of pod formation.
Multiple rounds of pod formation continue but the cycle slows down until eventually there are only small intracellular clusters of UPEC. These bacteria do not proliferate, but form a quiescent reservoir in the bladder which can last for months without overt UTI symptoms. Reactivation of these dormant bacteria may lead to a UTI recurrence. Thus, UPEC cleverly usurps the bladder and uses it as both a culture tube and a hiding place.