Effects of Cecropin Peptides on Aquatic Animal Pathogens and Shrimp Hemocytes

Abstract

In this paper, the effects of the well-characterized antimicrobial amphipathic peptides (cecropins A and P1) on pathogens of aquatic organisms were assessed. Results showed that cecropins inhibited growth of 15 strains of bacteria, including Gram-negative bacteria : Aeromonas hydrophila, A. salmonicida, Photobacterium damselae subsp. damselae, Pseudomonas anguilliseptica, Vibrio alginolyticus, V.anguillarum, V.carchariae, V.harveyi, V.ordalii, V.parahaemolyticus, V. tubiashii and V. vulnificus biogroup I. Cecropins also inhibited growth of two strains of the yeast Debaryomyces hanseni, pathogenic to freshwater prawn Macrobrachium rosenbergii. Minimum inhibitory concentration (MIC) of cecropin A ranged from 0.98 to 7.81μM and minimum bactericidal concentration (MBC) ranged from 3.90 to 15.59μM against the most prevalent vibrios pathogenic to cultured shrimp. A higher level of cecropin was required in a high salt environment to exhibit the effect against the pathogens. Influence of NaCl on bactericidal activity of cecropin A was also assayed. ⁵¹Cr-release assay showed a non-cytotoxic effect of cecropin A on shrimp (Penaeus monodon) hemocytes at MBC, but cytotoxic effect at 50μM (3.2-fold MBC) or higher concentration. This suggests that cecropin peptides may be difficult to be applied in vivo to treat infected marine shrimp.