Murine model of Salmonella infection

Laboratory animals Female BALB/c mice (6–8 weeks old) were purchased from Beijing Vital River Laboratory Animal Technology Co. Ltd (Beijing, China). All mice were maintained in a specific pathogen-free environment. Mice infections were performed as previously described [29 (link),42 (link)]. Overnight bacterial cultures were 1:100 diluted and cultured under SPI-1-inducing conditions (high salt, low O₂) to an OD₆₀₀ of 0.6 (late-exponential phase). The collected bacteria were serially diluted to either 5×10⁷ CFU/ml in PBS (for oral infection) or 1×10⁵ CFU/ml in 0.9% NaCl (for i.p. infection). For oral infections, mice were given a single dose of 20 mg streptomycin 24 h prior to infection, followed by oral gavage with 5×10⁶ CFU of indicated S. Typhimurium strains in 0.1 ml PBS. For systemic infections, mice were given 1×10⁴ CFU of indicated S. Typhimurium strains in 0.1 ml 0.9% NaCl by i.p. injection.
The infected mice were monitored daily and the survival rates were recorded. For CFU enumeration experiments, the infected mice were euthanized 5 days post-infection (oral infection) or 3 days post-infection (i.p.). Ileum, spleen and liver were harvested, homogenized in PBS, diluted and then plated on LB plates for determination of CFU. Experiments were repeated two or three times.