2.7. S. aureus Sepsis Mouse Model

For survival analyses in the S. aureus sepsis model, immunized BALB/c mice were intravenously infected with S. aureus and monitored for survival for 10 days after infection [24,25]. The lethal doses of the S. aureus strains MRSA252, JN-75, CQ-19, GZ-02 and KM-22 were determined to be 6.0 × 10⁸, 3.0 × 10⁸, 5.0 × 10⁸, 7.0 × 10⁸ and 2.0 × 10⁸ colony-forming units (CFUs)/mouse, respectively. To measure bacterial burdens in the sepsis model mice, a sub-lethal dose (3.0 × 10⁸ CFUs/mouse) of MRSA252 was intravenously administered. The peripheral blood was collected in heparin anticoagulant tubes. In addition, kidney and spleens were removed, weighed and homogenized in 1 mL of PBS 1 or 3 days after infection. All samples were then plated on MHA plates at a 10-fold serial dilution and cultured at 37 °C overnight. The number of CFUs per gram of tissue (CFUs/g) was calculated from each plate.