Effect of single or double administration of Esc(1–21)-1c (panel a); LL-37 and colistin (panel b) on the number of viable P. aeruginosa. The effect of single or double dosage of Esc(1–21)-1c on total leukocytes was also investigated (panel c). Bacterial burden (CFU) in the lung and spleen of infected mice was determined at 24 hours after bacterial infection. Animals were intra-tracheally infected with PAO1 cells. The peptides were instilled intra-tracheally, at 2 μg (0.1 mg/kg) at 2 hours (for single administration) and at 2 hours and 12 hours (for double administration) after bacterial infection. The numbers of viable Pseudomonas cells in the lung and spleen as well as the number of inflammatory cells in the BAL were counted at 24 hours after the infection, as described above. Results are mean ± SEM from three independent experiments; n = 4–6 mice for each treatment group. Following one-way analysis of variance (ANOVA), posthoc comparisons were made using the Dunnett’s multiple comparison test when the P-value was significant (p < 0.05). *p < 0.05, **p < 0.01 for peptide-treated animals versus PBS-treated mice.