In this work, the potential antimicrobial role and mechanism of action of a-helix domain of trout and salmon IL-8 against Eschericia coli, Pseudomonas aeruginosa and Staphylococcus aureus was investigated. By an in silico analysis of the primary structure of IL-8 from Oncorhynchus mykiss and salmo salar, it was evidenced that gamma-core motif was present, as in the vast majority of kinocidins. The alpha-helix domain of IL-8 (alpha lL-8) was synthesized by solid phase peptide synthesis and showed a tendency to form an alpha-helix conformation, as revealed by circular dichroism. Additionally, it was demonstrated that alpha IL-8 from both species showed antimicrobial activity against E. coli, P. aeruginosa and S. aureus. Membrane permeabilization and co-localization assay, as well as scanning electron microscopy, showed that these peptides were accumulated on the cell surface and in the cytoplasm, suggesting that they were capable of permeabilizing and disrupt the bacterial membranes and interact with cytoplasmic components. Our results represent the first analysis on the antimicrobial function of IL-8-derived peptide from salmonids. (C) 2018 Elsevier Inc. All rights reserved.