Blood infection model.

Actively immunized (10 days after second booster vaccination, i.m.) or passively immunized BALB/c mice were challenged with 100 μl of a lethal or sublethal dose of S. aureus strains by tail vein intravenous injection. For the lethal dose challenge, mice were infected with 5 × 10⁷ CFU of USA300, Newman, Staph1510, or Staph1610. Staph1310 was administered in 3.5 × 10⁷ CFU. The well-being of infected mice was monitored daily for 14 days. The mice were sacrificed when a humane endpoint was reached or when they had suffered a >20% weight loss. For sublethal dose challenge, animals were injected with 2 × 10⁷ CFU of USA300. The blood samples were collected within 6 h after the sublethal challenge. The spleens and lungs were removed 4 days after the sublethal challenge and homogenized. CFU were enumerated following serial diluting and plating on BHI agar. In cytokine depletion experiments, anti-mouse IFN antibody (clone R4-6A2), anti-mouse IL-17A antibody (clone 17F3), and the corresponding isotype control antibodies were purchased from Bio X Cell. Mice received 300 μg of antibodies or isotype control via intravenous injection 1 day prior to infection and on days 1 and 4 postinoculation.