Comparative mode of action of antimicrobial peptide melimine and its derivative Mel4 against Pseudomonas aeruginosa

Abstract

Melimine and Mel4 are chimeric cationic peptides with broad spectrum antimicrobial activity, and recent investigations have shown that they are highly biocompatible with animal model and human clinical trials. The current study examined the mechanism of action of these two antimicrobial peptides against P. aeruginosa with a series of investigations. Antimicrobial activities were determined by MIC and MBC. Endotoxin neutralization was determined using the LAL assay, effect on the cytoplasmic membrane was evaluated using DiSC(3)-5 and Sytox green stains, and Syto-9 and PI dyes using flow cytometry. Release of cytoplasmic materials (ATP and DNA/RNA) were determined using ATP luminescence and increase in OD260nm. The ability to lyse bacteria was studied by measuring a decrease in OD620nm. The MIC of the peptides remained low against P. aeruginosa strains, which showed efficient neutralization of LPS, indicating their role in the anti-pseudomonas and LPS binding activities. Both AMPs rapidly (starting at 30 seconds) depolarized P. aeruginosa cytoplasmic membrane leading to reduction in viability. Melimine was responsible for more ATP release (75%) compared to Mel4 (36%) (P<0.001) following two minutes exposure. For both peptides, Sytox green entered cells after five minutes of incubation. Flow cytometry demonstrated that both the AMPs permeabilized the cell membrane at 30 minutes and followed by increasing permeability. Similar results were found with DNA/RNA release experiments. Overall, melimine showed higher ability of membrane disruption, cell lysis compared to Mel4 (P<0.001). Knowledge regarding mechanism of action of these two AMPs would be helpful in making them as anti-pseudomonas drug.