Evaluation of the Antimicrobial Activity of an Extract of -Infected Larvae Produced Using an Automatic Injection System.

In the present study, we developed an automatic mass-injection system (AMIS) to produce an extract of infected larvae (iHIL-E) and then evaluated antimicrobial peptide (AMP) expressions and assessed the antimicrobial activity of iHIL-E against various pathogens and species. AMP gene expressions were assessed by real-time quantitative polymerase chain reaction (PCR) and the antimicrobial activities of iHIL-E were estimated using a radial diffusion assay and by determining minimal inhibitory concentrations. Results showed that the antimicrobial activity of HIL extract was effectively enhanced by infection and that the gene expressions of cecropin 3 and defensin 3 (antimicrobial peptides) were up-regulated. iHIL-E also prevented the growths of , , and (MICs 200, 500, and 1000 µg/100 µL, respectively) and demonstrated high protease resistance. Moreover, the growths of methicillin-resistant , antibiotic-resistant and AMP-resistant bacteria, , and were significantly suppressed by iHIL-E. In addition, although iHIL completely cleared species at concentrations of >200 µg/100 µL, species were unaffected by iHIL at concentrations of <1000 µg/100 µL. The present investigation shows that the devised automatic mass injection system is effective for the mass production of the extract of infected HIL and that this extract is a novel, natural, protease-resistant, antibiotic candidate with broad-spectrum antibiotic activity.