Antimicrobial peptides protect coho salmon from Vibrio anguillarum infections

Fish losses from infectious diseases are a significant problem in aquacultu re world wide. Therefore, we investigated the ability of cationic antimicro bial peptides to protect against infection caused by the fish pathogen Vibr io anguillarum. To identify effective peptides for fish, the MICs of certai n antimicrobial peptides against fish pathogens were determined in vitro. T wo of the most effective antimicrobial peptides, CEME, a cecropin-melittin hybrid peptide, and pleurocidin amide, a C-terminally amidated form of the natural flounder peptide, were selected for in vivo studies. A single intra peritoneal injection of CEME did not affect mortality rates in juvenile coh o salmon infected with V anguillarum, the causative agent of vibriosis. The refore, the peptides were delivered continuously using miniosmotic pumps pl aced in the peritoneal cavity. Twelve days after pump implantation, the fis h received intraperitoneal injections of V. anguillarum at a dose that woul d kill 50 to 90% of the population. Fish receiving 200 mu g of CEME per day survived longer and had significantly lower accumulated mortalities (13%) than the control groups (50 to 58%). Fish receiving pleurocidin amide at 25 0 mu g per day also survived longer and had significantly lower accumulated mortalities (5%) than the control groups (67 to 75%). This clearly shows t he potential for antimicrobial peptides to protect fish against infections and indicates that the strategy of overexpressing the peptides in transgeni c fish may provide a method of decreasing bacterial disease problems.