Evaluation of antibacterial activities of hemolymph and methanol extracts from black soldier fly (Hermetia illucens)

Abstract

Abstract Black soldier fly (BSF) has been recently recognized as a promising source of antibacterial substances such as antimicrobial peptides (AMPs) and medium-chain fatty acids (MCFAs). This study aimed to isolate and identify the antibacterial activities of hemolymph and methanol extracts from BSF. The BSF larvae hemolymph increased the growth of bacteria which is likely due to its nutritional effects. However, the bacteria (Listeria monocytogenes, Staphylococcus aureus, Salmonella typhimurium, and Escherichia coli) treated with the hemolymph from bacteria inoculated BSF larvae showed slower growth when compared with the bacteria treated with the unchallenged hemolymph, and such a difference was dramatically eliminated by proteinase K and proteins/peptides between 3-10 kDa were the most active substances that affected the growth of bacteria. However, the antibacterial activity of BSF hemolymph was not strong enough to develop a visible inhibition zone in the Zone of Inhibition test against any of the four bacteria strains above. Methanol extracts from III instar BSF larvae, V instar BSF larvae, and BSF prepupae showed strong antibacterial activities in the Zone of Inhibition test against the four bacteria strains, and it is resistant to proteinase K treatment. The antibacterial activity and the percentage of fatty acids in the methanol extracts increased with age. Heating at 130 °C for 60 min significantly improved the antibacterial ability of methanol extracts against Staphylococcus aureus without changing its fatty acid profile. In conclusion, bacteria-inoculated BSF larvae develop AMPs in hemolymph which exhibit weak antibacterial activities. The methanol extracts of BSF can be produced in large quantities using larvae and have strong antibacterial activity which is attributed to lauric acid and some unknown compounds.