Antimicrobial activity of an artificially designed peptide against fish pathogens

Antimicrobial peptides (AMPs) are considered alternatives to classical antibiotics and may become an excellent candidate for tackling antimicrobial resistance in aquaculture. Designing novel antimicrobial peptides for curbing antimicrobial resistance in aquaculture is paramount in one health approach. In this study, a short and compositionally simple peptide, KK16, was designed. KK16 is amphipathic with a net charge of + 6. Molecular docking results revealed that KK16 has a strong affinity towards two virulence proteins of Aeromonas sobria; aerolysin and outer membrane protein (omp). The peptide was synthesised using Fmoc-chemistry, and its antimicrobial efficacy was evaluated in vitro against A.sobria, A. salmonicida, Edwardsiella tarda, A. hydrophila, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis and methicillin-resistant S. aureus. The KK16 AMP showed potent activity against the tested bacterial pathogens as revealed by the MIC and MBC, ranging from 7.81 to 500 µM, and 15-900 µM, respectively. Moreover, the peptide was stable at higher temperatures and retained its activity in presence of serum and salt. The peptide displayed less haemolytic and cytotoxic activity even at higher concentrations. In peptide-DNA binding assay, KK16 showed its binding potential with bacterial genomic DNA and thus, may interfere with replication. Fluorescent microscopy revealed the uptake of propidium iodide by peptide treated bacterial cells, indicating its membrane disruption activity. In in vivo experiment, KK16 peptide completely inhibited the growth of Saprolegnia parasitica fungus at ≥ 30 µM peptide concentrations in embryonated fish eggs. The results indicate that KK16 peptide is stable, possess potent antibacterial and antifungal activity, less cytotoxic to host cells, and hence may prove to be a promising anti-infective agent for combating common bacterial and fungal infections.