Scorpion venom-derived Opis16a shows potent membrane-destabilising Gram-negative activity and promising in vivo topical efficacy

Abstract Antimicrobial peptides (AMPs) are lead candidates for antibacterial drug development, especially against multidrug-resistant Gram-negative bacteria. Previously, we showed that Opis16a, a novel scorpion venom-derived AMP, exhibits broad-spectrum activity against drug-resistant Gram-negative strains with minimal toxicity to mammalian cells. However, its mechanism of action remained unclear. Here, we show that Opis16a rapidly kills Gram-negative bacteria by targeting and disrupting their membranes, with strong bacterial selectivity over HaCaT and HepG2 cell lines. Mechanistic studies in Escherichia coli and a clinically relevant multidrug-resistant Acinetobacter baumannii strain reveal that Opis16a interacts with lipopolysaccharides, destabilising the outer membrane and causing inner membrane depolarisation and permeabilisation within minutes. Opis16a’s strong activity (MIC: 8 µg/mL), selectivity, and membrane disruption, along with its serum stability, translates into successful therapy in an in vivo Galleria mellonella model of gentamicin-resistant A. baumannii wound infection. Opis16a emerges as a novel membrane-destabilising AMP with promising potential for topical use against resistant Gram-negative infections.