Decreased cellular adhesion to the ECM and rearrangement of the cytoskeleton may facilitate the migration of Leptospira through endothelial barriers as it disseminates from the site of inoculation. To further explore the possibility that actin rearrangements are triggered by Leptospira infection at the functional level, endothelial cells plated in chamber slides were infected at an MOI of 10 for 1 hour and 3 hours. As shown in Figure 1 , the bacteria were clearly more adherent to the cells than to the extracellular space, and the pathogenic bacteria caused dramatically more significant alterations in cellular morphology and integrity of the cell layer than did the non-pathogenic bacteria. The earliest change noted was a reduction in cortical actin (so the cell edges are less defined) and appearance of gaps in confluent cell layers, followed by loss of stress fibers and rounding of the cells. The images shown in Figure 1 are from cell layers that were just below confluence prior to infection, to allow better visualization of changes in individual cells. For example, while the cortical actin has largely disappeared in cells infected with L. interrogans Canicola by 1 hour postinfection, and stress fibers have disappeared and cell rounding is evident by 3 hours, the cells are largely unaffected at the same time points after infection with L. biflexa Patoc (Figure 1 ). L. biflexa Endothelial Cell Responses to Leptospira www.plosntds.org does adhere to mammalian cells in culture less efficiently than does L. interrogans (as shown and reviewed in [17] ), but even when bacterial contact with the cells was facilitated by centrifugation, the L. biflexa caused little disruption to cellular morphology and cell layer integrity (data not shown).