ViPS Expression in Typhimurium Mutant

Mice were infected with a chimeric strain of S. Typhimurium (strain RC60) that expresses the S. Typhi genes necessary for ViPS synthesis, export, and regulation as in S. Typhi (25 (link)). Strain RC60 was grown to an OD₆₀₀ of ~1.0 in Luria–Bertani (LB) broth with 10 mM NaCl. The expression of ViPS was assessed by a slide agglutination test using a commercial Vi mAb reagent (Statens Serum Institute Diagnostica, Copenhagen, Denmark; lot 188L-8). Bacteria were washed twice in Dulbecco’s PBS (DPBS), and 100 μl of DPBS containing 3 × 10⁴ CFU was injected i.p. or i.v. At 3 d postinfection liver and spleen were collected, and the tissues were processed using a Minilys tissue homogenizer (Bertin Technologies, Montigny-le-Bretonneux, France). The bacterial burdens in the liver and spleen homogenates, as well as blood collected into anticoagulant, were determined by plating serial 10-fold dilutions on LB agar plates followed by counting CFU (16 (link), 26 (link), 27 (link)).