ViPS-Mediated Protection Against Salmonella

To test the relative protection conferred by ViPS immunization, mice were infected with a chimeric strain of S. Typhimurium (strain RC60) that expresses S. Typhi genes necessary for ViPS synthesis, export, and regulation as in S. Typhi (32 (link)). Strain RC60 was grown to an OD⁶⁰⁰ of ~1.0 in Luria Bertani (LB) broth containing 10 mM NaCl. Bacteria were washed twice in DPBS and 2x10⁴ cfu in 100 μl of DPBS was injected i.p. or i.v. The bacterial burden in the blood, liver, and spleen was measured 3 days later as described previously (30 , 33 (link)), since mice on BALB/c or C57BL6 background succumb to Salmonella infection by 5 days post-infection at this infectious dose due to the presence of a susceptible Nramp1 allele (33 (link)–35 (link)). Tissues were processed using a Minilys tissue homogenizer (Bertin Technologies, Montigny-le-Bretonneux, France) and bacterial burden in these tissue homogenates or in blood was measured by counting cfus on LB agar plates.