Black Soldier Flies Show Potential as Source of Antimicrobial Compounds

Helicobacter pylori is a pathogenic gram-negative bacterium that infects two thirds of people worldwide. In many individuals, it causes no symptoms, but it can cause gastric inflammation, ulcers, and, in some instances, stomach cancer. An increasing percentage of H. pylori strains are resistant to antibiotics, creating a need for antimicrobial compounds from new sources. One potential source of such compounds are larvae of the black soldier fly (Hermetia illucens).

Black soldier flies live in decomposing, bacteria-rich organic material such as manure, and they are a promising subject for antibiotics research because living in a bacteria-rich environment demands a potent immune system. Daniela Alvarez and colleagues from an international research team from Peru and France based at the Universidad Peruana Cayetano Heredia have isolated small amino acid chains called peptides from black soldier fly larvae, and they’ve discovered that several of the peptides had strong anti-H. pylori activity. Their research was reported in December 2019 in the open-access Journal of Insect Science.

Antimicrobial peptides are part of the innate immunity of insects. Previous research in 2018 identified 53 genes in black soldier flies that might code for antimicrobial peptides. In the study by Alvarez and colleagues, they isolated peptides from black soldier fly larvae and tested their effect on H. pylori. To induce an immune response, some lab-maintained larvae were injected with non-pathogenic Escherichia coli bacteria. Larvae in a control group were not injected with E. coli.

The investigators collected peptides from the hemolymph of larvae with a syringe, purified the peptides, and then tested for anti-H. pylori activity using an inhibition zone assay. In this test, agar plates were created containing H. pylori cells. Then holes were punched in the agar and test samples of peptides were added to the holes. After an incubation period of 72 hours, the investigators measured how far into the agar a peptide sample inhibited H. pylori. They found over 90 peptides in their analysis, four of which they determined to have pronounced anti-H. pylori activity. Only larvae injected with E.coli were found to have anti-H. pylori antimicrobial peptides, indicating that these peptides were produced in response to bacterial exposure.

When asked about next steps in this research, co-author Kevin Wilkinson says, “The first additional step would be to determine the sequence of purified peptides. This would allow for large-scale preparation of the peptide. That way, we could get a clearer picture of in vitro anti-H. pylori activity against different antibiotic resistant strains.”

Wilkinson and colleagues are also interested in testing if any of the isolated antimicrobial peptides have activity against other pathogens. “In its fight against E. coli,” Wilkinson says, “Black soldier flies produced anti-H. pylori antimicrobial peptides. Because black soldier flies were fighting an E. coli infection, it is likely that the isolated peptides may inhibit some other microbes as well, including E. coli and related bacteria.” This potential cross-reactivity could offer additional practical benefits to treat infections.

Alvarez and colleagues are also interested in the other antimicrobial peptides discovered in their study. They found that black soldier fly larvae produced over 90 peptides in response to being inoculated with E. coli. “What are the other peptides doing?” Wilkinson asks. “Perhaps these may have activity against other medically or scientifically important microbes.”

This study is exciting in showing that insects have potential as sources of antimicrobial compounds for medical use. Given the immense diversity of insects as a class, this suggests that their bioprospecting potential is huge. Such new compounds could be particularly valuable in instances of drug-resistant bacteria such as H. pylori or other difficult-to-treat infections.

John P. Roche, Ph.D., is an author, biologist, and educator dedicated to making rigorous science clear and accessible. Director of Science View Productions and Adjunct Professor at the College of the Holy Cross, Dr. Roche has published over 200 articles and has written and taught extensively about science. For more information, visit https://authorjohnproche.com.