The rapid increase of plant diseases caused by bacterial phytopathogens calls for an urgent search for new antibacterials. Antimicrobial compounds of natural origin stand up as frontiers in the attempts of the antibiotic overuse replacement. With this in mind, the Hermetia illucens (H. illucens) larvae have recently gained attention as a promising approach to fulfill this need. This study aimed to isolate the active constituents of H. illucens larvae fat and to estimate its antimicrobial capacity. We discovered the best composition of extracting solution retaining the pronounced antimicrobial activity of the extract. Using gas chromatography-mass spectrometry (GC-MS), we identified the unique natural array of fatty acids as the major constituents of the acidified water-methanol extract (AWME) as having new antimicrobial potency. In standard turbidimetric assay, the minimum inhibitory concentration (MIC) of the AWME was 0.78 mg/mL after 24 h of incubation for all five tested phytopathogenic bacteria strains: Pantoea agglomerans, Xanthomonas campestris, Pectobacterium carotovorum subsp. carotovorum, Pectobacterium atrosepticum, and Dickeya solani. The minimum bactericidal concentration (MBC) ranged from 0.78 to 1.56 mg/mL against all tested strains after 24 h of incubation. The inhibition zone size of AWME (INZ) at 50 mg/mL concentration was in the range 12.2 ± 0.56 to 19.0 ± 0.28 mm, while zone size for the positive control (penicillin-streptomycin) (5000 IU/mL-5000 µg/mL) was in the scale of 20.63 ± 0.53 to 24.0 ± 0.35 mm as revealed by standard disk diffusion assay. For the first time, our findings indicated the substantial antibacterial potential of AWME of H. illucens larvae fat against these actual phytopathogens, thus paving the way for further research to determine the mechanism of action in crop protection.
Keywords: antibacterial activity; black soldier fly; fatty acids; larvae extract; phytopathogenic bacteria.