Antibacterial peptides from black soldier fly (Hermetia illucens) larvae: mode of action and characterization

Antibacterial peptides from black soldier fly larvae extract were prepared using Flash column chromatography. Three out of five fractions (F₂, F₃ and F₄) showed antibacterial activity against Listeria monocytogenes DMST 17303 with a minimum inhibitory concentration (MIC) of 1 mM, followed by Salmonella enterica Enteritidis DMST 15679 and Escherichia coli O157:H7 DMST 12743 with a MIC ranging from 4 to 8 mM. Due to the higher yield, F₂ and F₃ were further analyzed on their mode of action against L. monocytogenes DMST 17303. Both fractions, particularly F₂, exerted antibacterial activity through inducing bacterial cell membrane disintegration and interaction with intracellular compounds including fatty acids, proteins, and nucleic acids. The F₃ did not show significant hemolytic activity up to 4 mM, while F₂ showed lower than 5% hemolysis up to 8 mM. Time-to-kill analysis revealed that F₂ was more effective and exerted a sustainable killing effect after 2 and 4 h, depending on the concentration of 1 and 2×MIC, respectively, while the F₃ at 2×MIC could completely kill the test bacteria within 24 h. Among the identified peptides in the fractions, those with charged, either positively or negatively, and moderate hydrophobicity of ranging 6.68-15.70, namely CGPPRQGPFPR, HLEEELK, LEEAEERAD, TEELEEAKKK, and KGNSELEEAKKK, are potential antimicrobial peptides.