Exogenous addition of BDSF caused the reduction of the transcriptional expression of T3SS master regulators and effectors, as determined by using RT-PCR analysis (A), and of secretion of ExoS determined by western blotting analysis (B). Bacteria were grown in LB medium to an OD600 of 1.5, supplemented with 5 mM NTA and BDSF at a series of final concentrations as indicated. For each RNA sample, two dilutions (5, 50 ng) were used as templates for RT-PCT reaction. For the western blotting analysis, the extra-cellular proteins in supernatants were collected by trichloroacetic acid precipitation and separated by 10% SDS-PAGE. The proteins were transferred onto nitrocellulose membrane and blotted with anti-ExoS antibody.