Effects of cecropin peptides on bacteria pathogenic to fish

The antibacterial effects of synthetic cecropin B and cecropin P1 were test ed against the fish-pathogenic bacteria Vibrio anguillarum, Vibrio salmonic ida, Aeromonas salmonicida, Edwardsiella ictaluri and Yersinia ruckeri. Bot h cecropins were arrive against all bacteria tested, bur the effect was str ongly influenced by the growth media used. In brain heart infusion medium, the minimum inhibitory concentrations of cecropin B ranged from 0.3 to 1.3 mu M and from 0.3 to 1.0 mu M for cecropin P1, except for E. ictaluri, whic h was noticeably less sensitive to cecropin P1 (61 mu M). The present autho rs have compared the bactericidal activity of these two peptides, showing t hat the killing rate for the selected bacteria was higher for cecropin B th an for cecropin P1. V. anguillarum was the most sensitive to the cecropins, and in the present study, no colony forming units were detected after 4 an d 8 min of treatment with cecropin B and P1, respectively. Electron microsc opy was performed to document the effect of cecropin on the bacterial surfa ce.