Antimicrobial activity of lipids extracted from Hermetia illucens reared on different substrates

Abstract

As the problem of antimicrobial resistance is constantly increasing, there is a renewed interest in antimicrobial products derived from natural sources, particularly obtained from innovative and eco-friendly materials. Insect lipids, due to their fatty acid composition, can be classified as natural antimicrobial compounds. In order to assess the antibacterial efficacy of Hermetia illucens lipids, we extracted this component from the larval stage, fed on different substrates and we characterized it. Moreover, we analyzed the fatty acid composition of the feeding substrate, to determine if and how it could affect the antimicrobial activity of the lipid component. The antimicrobial activity was evaluated against Gram-positive Micrococcus flavus and Gram-negative bacteria Escherichia coli. Analyzing the fatty acid profiles of larval lipids that showed activity against the two bacterial strains, we detected significant differences for C4:0, C10:0, C16:1, C18:3 n3 (ALA), and C20:1. The strongest antimicrobial activity was verified against Micrococcus flavus by lipids extracted from larvae reared on strawberry, tangerine, and fresh manure substrates, with growth inhibition zones ranged from 1.38 to 1.51 mm, while only the rearing on manure showed the effect against Escherichia coli. Notably, the fatty acid profile of H. illucens seems to not be really influenced by the substrate fatty acid profile, except for C18:0 and C18:2 CIS n6 (LA). This implies that other factors, such as the rearing conditions, larval development stages, and other nutrients such as carbohydrates, affect the amount of fatty acids in insects. KEY POINTS: • Feeding substrates influence larval lipids and fatty acids (FA) • Generally, there is no direct correlation between substrate FAs and the same larvae FAs • Specific FAs influence more the antimicrobial effect of BSF lipids.

Keywords: Antimicrobial resistance; Black soldier fly; Fatty acids; Insects oil.

Fig. 1

Correlation between FAs of the substrate and the larvae. X axis report % on FA in substrates, Y axis report % on FA in larvae. Data are presented as mean of three biological replicates. p value: C12 = 0.4803; C14 = 0.7032; C16 = 0.5982; C16:1 = 0.3860; C17 = 0.9660; C18 = 0.0045; C18:1 CIS9 = 0.8181; C18:2 = 0.0306; C18:3 n3 (ALA) = 0.3045; C22 = 0.2368

Fig. 2

Microbiological assay and the growth inhibition zone developed around the crude fat extracted from BSFL fed on different substrates ((a) strawberry, (b) orange, (c) fresh dairy manure, (d) AMP, (e) Gainesville diet, f tangerine) against Escherichia coli in A and Micrococcus flavus in B