Abstract
Simple SummaryIn this investigation, we found antimicrobial activity of the extract of Lactobacillus casei–infected Hermetia illucens larvae (HIL) against Salmonella species. The result demonstrates that the extract is a powerful natural antibiotic and preservative.The expressions of antimicrobial peptides (AMPs) in the larvae of the black soldier fly, Hermetia illucens, were significantly increased by pathogen or stimulant induced innate immunity activation. We immunized H. illucens fifth instar larvae with five different Lactobacillus species, that is, Lactobacillus acidophilus, L. brevis, L. casei, L. fermentum, or L. delbrueckii, to induce the mass production of AMPs and selected optimal immune inducers. Antimicrobial activities in hemolymph and H. illucens larvae (HIL) extract were evaluated against three salmonella species (Salmonella pullorum, Salmonella typhimurium, and Salmonella enteritidis). Highest antimicrobial activity was shown by the hemolymph of HIL immunized by L. casei and its activity was closely linked with the inductions of cecropin 1 (HiCec1) and defensin 1 (HiDef1) gene expressions. Furthermore, antimicrobial activity in hemolymph was stable to heat and pH and the growth of three Salmonella species were dramatically suppressed by HIL hemolymph and extract after immunization with L. casei. The minimal inhibitory concentration (MICs) of L. casei-immunized HIL extract against Staphylococcus aureus, Escherichia coli, and Salmonella species ranged from 100~200 µg/100 µL and no cytotoxicity to CaCo-2 and L929 cells were observed in the concentration range 100~40,000 µg/100 µL. Taken together, the present investigation demonstrates that L. casei-immunized HIL extract is a powerful natural antibiotic and preservative that can prevent contamination by Salmonella species.
Highlights
Antibiotics are used to treat infectious diseases and prevent infections in humans and animals and to promote animal growth and have played leading roles in the intensive farming of livestock
antimicrobial peptides (AMPs) inducer, we evaluated antimicrobial activity of H. illucens larvae (HIL) immunized with five Lactobacillus species and assessed the bactericidal activities of an extract of HIL immunized with a selected Lactobacillus species to determine the potential use of the extract as a natural antibiotic or preservative
We investigated whether L. casei-immunized HIL extract has the potential to be used as a natural antibiotic or feed additive with antimicrobial activity
Summary
Antibiotics are used to treat infectious diseases and prevent infections in humans and animals and to promote animal growth and have played leading roles in the intensive farming of livestock. Abuse of in-feed antibiotics has caused many problems, such as the appearance of antibiotic-resistant bacteria, antibiotic residues in livestock products, weakening of disease resistance in livestock, and ecosystem pollution [1,2,3]. To address these problems, the European Union prohibited the use of veterinary antibiotics for growth promotion from 2006, whereas in Korea, after a phased reduction. AMPs secreted by the humoral immune response are classified by amino acid sequence and structure as cecropins, defensins, proline-rich peptides, glycine-rich peptides, and lysozymes and are found in various insects including Coleoptera, Diptera, Hymenoptera, and Lepidoptera [11,12,13,14,15,16]
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