4.5. Antimicrobial Activity Test Protocol

Peptide susceptibility tests on the reference bacterial strains were performed with the following procedures recommended by the Clinical and Laboratory Standard Institute (CLSI). The activity of five peptides was tested on the Mueller Hinton Broth II (Biocorp, Warsaw, Poland) using broth microdilution method on polystyrene 96-well plates (Kartell, Noviglio, Italy). Bacterial inoculum of ca. 5 × 10⁵ CFU/mL was added to each well and exposed to solutions of peptides at increasing concentrations (range 1–512 μg/mL). The plates were incubated overnight at 37 °C. MIC was assumed as the lowest concentration at which bacterial growth was no longer visible. All experiments were performed in triplicate.