Evaluation of Anti-bacterial Activity Induced by Penicillium mallochii in the Hemolymph of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Abstract

Anti-microbial peptides (AMPs) exhibit anti-bacterial, anti-fungal and anti-parasite activity and are essential effectors for the immune response of insects. Insect hemolymph contains AMPs, which are one of the sources of antibiotics effective on drug-resistant microorganisms. This study was conducted to induce antimicrobial activity in hemolymph by topical application of different doses of Penicillium mallochii conidia and its metabolite to Ephestia kuehniella larvae. Tetracycline antibiotic disks (TE-10 µg, Sigma), Sulfametaxozole trimethoprim (SXT-25 µg, Sigma), PBS, sterile water, and non-induced hemolymphs of larvae were used as control groups. In total hemolymph induced with metabolite extract, 24-h application was determined to be more effective on test bacteria than 48-h application. The largest zone diameter was observed against Escherichia coli (20mm) in hemolymph collected 24 h after metabolite application. Antimicrobial activity was highly increased (24h and 48h) when larvae were induced with P. mallochii conidial suspension. The largest zone diameter was observed against Proteus vulgaris and Klebsiella pneumonia (20 and 24 mm) in hemolymph collected 24 h after conidial suspension application. When larvae were induced with fungus metabolite and conidia, the zone of inhibition was 1.5-2.5-fold larger than that of the control hemolymph, indicating a higher antimicrobial activity after application. In general, this study provides a novel contribution to the knowledge regarding enhancement of antimicrobial activity in response to fungal infections in larvae.