Antibacterial efficacy of free phage and phage-MPs was examined in a CFTR knockout mouse model of acute lung infection with P. aeruginosa (PAO1-GFP). After 18 h of treatment, (a) bacterial load (n=6 mice for bacteria and bacteria+phage-MPs; n=7 for bacteria+phage, mean ± SD) and (b) phage load (n=3 mice for bacteria and bacteria+phage-MPs, 4 mice for bacteria+phage, mean ± SD) in lung homogenate were quantified. For (a-b), data were pooled from two independent experiments. One-way ANOVA was used to detect statistical differences followed by Tukey’s multiple comparison test with adjustment for multiple comparisons. *** p < 0.0001 vs. bacteria control, $ $ $ p < 0.0001 vs. bacteria+phage group. Data were collected on both male and female CFTR knockout mice. Measurements were taken from distinct samples. Images of histological sections of mouse lung stained with H&E at 18 h after treatment with (c) bacteria only, (d) bacteria + phage and (e) bacteria + phage-MPs. These are representative images from a total of five images taken for each group.