Salt resistance assay

A major hindrance to clinical application of defensin peptides is the interference of function by cationic salts, often referred to as salt sensitivity [29]. The effect of salt on antimicrobial activity of novel CAMPs against P. aeruginosa ATCC 27853 and S. aureus ATCC 29213 was determined by a colony count assay as described previously [14], in the presence of either 0, 50, 100, and 150 mM NaCl or 0, 0.5, 1, and 2 mM CaCl₂. Two peptide concentrations, 0.5 × MIC and 1 × MIC, were included. Medium without CAMP served as a negative control. Percent of killing was calculated using the following formula: (CFU_control - CFU_treated) / CFU_control × 100% [14]. All assays were performed in triplicate.