In vitro activity of the antimicrobial peptide magainin 1 against Bonamia ostreae, the intrahemocytic parasite of the flat oyster Ostrea edulis.

Magainins are peptide antibiotics with broad antibacterial and antiparasitic activities, originally extracted from the skin of Xenopus laevis. We investigated the effects of magainin 1 against Bonamia ostreae, the intrahemocytic parasite of the flat oyster Ostrea edulis. Viability of purified protozoa was assessed microscopically by the uptake of the vital dyes acridine orange and ethidium bromide. Following exposure to magainin 1, Bonamia viability was reduced in a dose-dependent manner. Within the peptide concentration of 500 micrograms/ml, the parasite viability was reduced by 94%. Electron microscopy showed membrane damage and release of cytoplasmic organelles in the injured Bonamia. The study of magainin 1 activity against Ostrea edulis hemocytes did not show any morphological change in the host cells, and the peptide did not impair the capabilities of hemocytes to produce chemiluminescence when stimulated to phagocytize zymosan particles. The possibility to genetically transform molluscs to generate disease-resistant organisms is currently under investigation. Antimicrobial peptides such as magainins may provide effective gene sequences to be manipulated.