Investigating the in vivo antimicrobial activity of a self-assembling peptide hydrogel using a Galleria mellonella infection model

Technological advances in protein biochemistry now enable researchers to modify the structure of peptides to enable them to possess self-assembling properties, forming hydrogels at low concentrations. Peptides can be altered further to provide multifunctional characteristics, for example to demonstrate antimicrobial properties. The aim of this paper is to investigate the in vivo toxicity and antimicrobial properties of a low molecular weight (naphthalene-2-ly)-acetyl-diphenylalanine-dilysine-OH (NapFFKK-OH) peptide hydrogel using an innovative waxworm (Galleria mellonella) model, as an alternative to mammalian/vertebrate testing. NapFFKK-OH hydrogels did not demonstrate any observable in vivo toxicity or death in Galleria mellonella over 5 days at concentrations studied (≤2% w/v). A dose dependent Log10 reduction in viable (CFU/mL) Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria implicated in nosocomial infections was observed over 72 hours. NapFFKK-OH was especially effective against in vivo infection models of Staphylococcus aureus with a significant 4.4 Log10 CFU/mL reduction in viable bacteria at 2% w/v after 72 hours. Our results show Galleria mellonella to be a useful model for preliminary determination of in vivo toxicity and antimicrobial efficacy profiles of novel nanomaterials, including peptide-based hydrogels. It contributes to the 3R principles of animal testing – reduction, refinement and replacement. The results also show NapFFKK-OH to be a promising alternative to standardly employed antimicrobials with the potential to be utilized as a novel therapeutic in the treatment and prevention of hospital infections.