(A) Dose–response curves for Ec DH10B incubated with increasing concentrations of huBPI, murine BPI (muBPI), scoBPI, or oyster BPI (osBPI; n = 3). (B) Bactericidal activity of huBPI, muBPI, scoBPI, and osBPI 500 nM against Pa PAO1 (n = 3). (C) Antibacterial activity of huBPI and scoBPI at concentrations of 20 and 500 nM against six MDR isolates of Pa obtained from five individual people with cystic fibrosis (PwCF). Isolates (isolates 2 and 5 in Table 1) that originate from the same donor are shown as a square. Mucoid isolates are displayed as filled symbols connected by continuous lines. (D) Images of a bacterial viability assay performed with one representative Pa MDR strain. Viable bacteria are seen in green and dead bacteria in red, respectively. Scale bars for 10 µm. (E) Transmission electron microscopy of the representative Pa MDR isolate shown in (D) after treatment with PBS (control) or scoBPI for 2 hr. Scale bars for 1 µm (left, middle) or 500 nm (right). Data are shown as individual values (A) or means ± SEM (B, C) of technical replicates using the same lots of BPI and bacteria in three separate assays (A, B). Relative colony-forming units (CFUs) are depicted (A–C). Statistical testing was performed using the Student’s paired t-test on the absolute CFUs (A–C). Statistical significance is indicated by p-values.