Fig 1.

(A) Diagram of flow chamber with uroepithelium cell culture. Flow to and from the substratum surface is maintained through the upper polycarbonate disc (mark 1) machined with connecting pipes and inner channels. Ongoing infection is observed in situ through the polycarbonate disc. A silicone gasket (mark 2) with central slit (mark 3) defines the flow channel dimensions on a cell cultured glass slide. (B) Uropathogenic cascade in vitro. The scheme outlines the complete cycle of UPEC intracellular infection induced in vitro. UPEC bacteria are seeded onto an FC-BEC culture (upper left) and subsequently induced to colonize the surface (upper right). During coculturing of bacteria and BEC, single bacteria invade BECs and initiate intracellular colonization (lower right). After elimination of extracellular bacteria and during continuing coculture of the BEC layer with intracellular bacteria, some cells become extensively colonized, leading to their eruption (lower left). During escape from colonized, loosely attached BECs (indicated with arrows in the lower left panel), a secondary colonization initiates in the form of distinct aggregates of filamentous bacteria associated with the BEC (lower left) or of loosely dispersed bacteria, depending on the urine concentration. The filamentous UPEC bacteria can revert to single cells capable of reinvasion, which may lead to subsequent rounds of the uropathogenic cascade. Upper images and lower left image are from in situ FC microscopy, showing the undisturbed bacterial colonization. UGM, uroepithelium growth medium; pep, peptone; glu, glucose; genta, gentamicin. Bars, 100 μm (black) and 10 μm (white).