TtsA is required for typhoid toxin secretion. (A) Schematic representation of the S. Typhi pathogenicity islet encoding typhoid toxin. (B) Sty1889 (TtsA) is required for typhoid toxin secretion. Henle-407 cells were infected with S. Typhi expressing chromosomally encoded 3 × FLAG-epitope-tagged CdtB, a ΔttsA isogenic mutant, or the complemented ΔttsA mutant. Twenty-two hours after infection, cells were stained with an antibody directed to the FLAG epitope (green) (to visualize CdtB), a rabbit antibody directed to S. Typhi LPS (red) and DAPI for DNA detection (blue). The bar represents 10 μm. (C) Western blot analysis of the strains used in panel (B). (D) TtsA expression profile during bacterial infection of cultured cells. At the indicated times after infection, cells were lysed and the levels of CdtB and TtsA were examined in CFU standardized samples by western blot analysis. CFU, colony-forming units; DAPI, 4,6-diamidino-2-phenylindole; LPS, lipopolysaccharide; WT, wild-type.