In vivo studies of the protection activity of ARD peptide HBc147-183 against S. aureus.

(A) Three-week old male ICR mice were challenged with a lethal dose of S. aureus ATCC 19636 and then divided into five separate groups for five different time points. At each indicated time point (n = 5), blood samples were collected, diluted and plated on BHI agar. The number of bacteria was counted the following day. A maximal bacterial load in the blood was observed at 2 h post-inoculation. The data were shown in mean ± SD. (B) ICR mice inoculated with a lethal dose of S. aureus as described above were treated by intraperitoneal injection with ARD peptide (10 mg/kg) at 1, 1.5 or 2 h post-inoculation, respectively. Each group contained 10 mice. All mice (100%) treated with the PBS control died at day 1, while treatment of ARD peptide at 1, 1.5 or 2 h post-inoculation protected the mice with survival rates of 100%, 70% and 40% after 7 days, respectively. (C) As described above, ICR mice were i.p. inoculated with S. aureus, followed by i.p. injection with PBS (n = 5) or 10 mg/kg ARD peptide (n = 5) at 1 h post-inoculation. At 4 h post-inoculation, blood, liver and spleen were collected. Liver and spleen samples were homogenized, diluted and, together with blood samples, plated on BHI agar. The number of bacteria was counted the following day. In comparison to mice treated with PBS, treatment of ARD peptide effectively reduced the bacterial load in blood, liver and spleen. (D) Quantitative comparison of bacterial loads in blood, liver and spleen samples of mice treated with PBS (open circle, diamond and square) versus ARD peptide HBc147-183 (solid circle, diamond and square). The line indicated the mean of bacterial load. **P