Mode of action of antimicrobial peptide P45 on Listeria monocytogenes

The mode of action of an antimicrobial peptide produced by Bacillus sp. P45 isolated from the intestine of the Amazonian basin fish Piaractus mesopotamicus was investigated. The antimicrobial peptide was purified from culture supernatants by precipitation with ammonium sulfate and gel filtration chromatography. The peptide has an EC50 of 300 AU (activity units) ml(-1) and kills all viable cells of Listeria monocytogenes with a concentration of 800 AU ml-1. A decrease in OD was observed when L. monocytogenes cultures were treated with the peptide, suggesting that cells were lysed. Transmission electron microscopy showed damage of the cell envelope and loss of protoplasmic material. The peptide P45 was bactericidal and bacteriolytic to L. monocytogenes. There is evidence that the mode of action is interefering at cell membranes and the cell wall. The knowledge of the mode of action of antimicrobial peptides is an essential step to consider their utilization in food or clinic.