Fig. 6. Treatment by C. difficile toxin B prevents actin polymerization but not ezrin recruitment induced by N. meningitidis. (A,B) Confluent monolayers of HUVECs were either left untreated (control) or treated with 1 ng/ml of C. difficile toxin B (ToxB) in starvation medium for 16 hours prior to the infection. Control and Tox-B-treated cells were then infected with the ROU strain of N. meningitidis for 4 hours. Tox B treatment was maintained during infection. Cells were double stained for F-actin and ezrin and the percentage of bacterial colonies recruiting ezrin (A) or F-actin-positive (B) was determined by immunofluorescence analysis. Results correspond to counts of 300 bacterial colonies in three distinct experiments. (C) xy section of double fluorescence labeling of F-actin (middle panel) and ezrin (right panel) in the same field. Analysis was performed by confocal microscopy at magnification x63. The localization of the bacterial colony in the same field is shown by phase contrast (left panel).