Hermetia illucens chitosan: indirect and direct antimicrobial activity of an innovative biopolymer for clinical and pharmaceutical applications

The increasing spread of antimicrobial resistance has prompted the search for innovative alternatives to conventional antibiotics. Chitosan, a biopolymer derived from chitin, is known for its broad-spectrum antimicrobial activity. This study evaluated both direct and indirect antimicrobial activity of chitosan obtained from Hermetia illucens, a novel and sustainable source compared to the traditionally crustacean-derived biopolymer. Chitosan produced from H. illucens larvae, pupal exuviae and adults, through heterogeneous and homogeneous deacetylation, was tested for both its indirect and direct antimicrobial effects. The indirect effect was evaluated by measuring the induction of Human Beta-Defensin-2 (HBD-2) expression in HaCaT keratinocytes stimulated with lipopolysaccharide of Salmonella typhimurium, a Gram-negative bacterium. The direct antimicrobial activity was assessed against Gram-positive pathogens (Enterococcus faecalis, Staphylococcus epidermidis, and Streptococcus agalactiae), using a microdilution assay and plate colony count. Results demonstrated significant bacteriostatic effects at 0.5 mg/mL, with some samples, particularly the homogeneous unbleached pupal exuviae chitosan and the heterogeneous unbleached larvae chitosan, comparable to or even superior to commercial chitosan in terms of biological activity. Furthermore, insect-chitosan significantly up-regulated HBD-2 expression, suggesting immunomodulatory activity. These findings validated H. illucens as a promising alternative source of chitosan with dual antimicrobial activity, and supported its potential use in clinical, pharmaceutical and biomedical applications. KEY POINTS: • Insect-chitosan activates innate immunity via strong HBD-2 induction • Chitosan samples showed notable growth-inhibition toward key Gram-positive strains • Hermetia illucens chitosans provide efficacy comparable or superior to the commercial biopolymer.