Fig. 5.

Display of S. typhi CDT activity and expression of cdtB require bacterial internalization. Henle-407 cells were infected with S. typhi or its isogenic invA mutant, which is unable to enter host cells. (A) Cells were examined 72 h after infection under a phase microscope for signs of intoxication. (Scale bar, 50 μm.) In addition, cells were infected with derivatives of S. typhi or its isogenic invA mutant encoding the cdtB::luc reporter fusion strain, and the luciferase activity at different times after infection was measured as indicated in Materials and Methods. (B) In all cases, values were standardized relative to the colony-forming units and the values obtained in cells 2.5 h after infection, which was considered 100%.