CATHELICIDIN ANTIMICROBIAL PEPTIDE ENHANCES PROTECTION OF CHANNEL AND CHANNEL-BLUE HYBRID CATFISH AGAINST Aeromonas hydrophila AND Edwardsiella ictaluri INFECTIONS

Worldwide, protection of fish against infectious diseases is a major challenge in aquaculture, and economic losses due to these diseases limit profitability.  The ability of antimicrobial peptides (AMPs), a class of highly conserved peptides known to possess direct antimicrobial activities against invading pathogens, was investigated for protection in channel and channel catfish female X blue catfish male hybrid catfish against infection caused by the catfish pathogens, Aeromonas hydrophila and Edwardsiella ictaluri.  To identify effective peptides, the minimum inhibitory concentrations (MICs) against fish pathogens and killing kinetics against A. hydrophila were determined in vitro.  Cathelicidins derived from alligator and sea snake exhibited potent and rapid antimicrobial activities against the tested catfish pathogens as compared to cecropin and pleurocidin AMPs.

When the peptides (50 µg/ml) were injected into fish and simultaneously challenged with each pathogen through immersion, increased survival rates in channel and hybrid catfish were observed for both cathelicidins (alligator and sea snake) as compared to other peptides and the infected control (Figure 1).  Serum lysozyme levels also increased in channel and hybrid catfish injected with both cathelicidins then challenged with E. ictaluri (Figure 2).  Increase in serum lysozyme is an indication of elevated immune response against bacterial infections.

These results clearly show the potential of cathelicidins to protect fish against bacterial infections and demonstrates a strategy that overexpressing the peptides in transgenic fish may provide a method of decreasing bacterial disease problems in catfish.