The efficacy of cathelicidin, an antimicrobial peptide in controlling disease causing bacterial pathogens in catfish 

Disease outbreaks in the aquaculture industry can lead to major economic losses if not managed properly, that is why one of the major goals in aquaculture is to ensure that the fish are being protected from infectious diseases. As a response, Dr. Rhoda Mae C. Simora from the College of Fisheries and Ocean Sciences, together with her research team studied the effectiveness of cathelicidin, an antimicrobial peptide which can be used against bacterial pathogens in catfish. 

Antimicrobial peptides (AMPs), a class of highly conserved peptides and are known to have the capacity to possess antimicrobial activities against pathogens which invade certain species. These antimicrobial peptides are one of the key components of the inherent immune system which are practically present in all species. These were evaluated for their ability to protect channel catfish (Ictalurus punctatus) and hybrid catfish (female Channel Catfish x male blue Catfish I. furcatus) against Aeromonas hydrophila, a fish pathogen which causes infection in catfish. The effectiveness of cathelicidin AMPs were evaluated by conducting in vitro and in vivo assay. In the in vitro assay, which means that it will be tested outside the living host, bacterial killing effect was conducted using five catfish pathogens namely, (1) Edwardsiella ictaluri, (2) Edwardsiella piscicida, (3) Aeromonas hydrophila, (4) Aeromonas veronii, (5) Flavobacterium columnare. Two types of cathelicidin were used, these were the alligator cathelicidin and the sea snake cathelicidin which were extracted from alligator and sea snake, respectively. These are known to have potent antibacterial properties. Their efficacy were compared with in vitro moth cecropin, AMP flounder pleurocidin, and the antibiotic control, ampicillin. Based on the in vitro assay, the most infected AMP are cathelicidins, meaning they are the most effective in terms of inhibiting the growth of bacteria at a little or small amount of concentration. 

Another assay was  created and they put together the result of the in vivo and in vitro assays. The AMPs were injected into channel and hybrid catfish for in vivo assay. At the end of the challenge period, the AMPs were injected into catfish fingerlings and these fingerlings were placed into tanks with bacteria. Survival was monitored for about 8-10 days but it was terminated during the 8th day since eighty percent (80%) of survival was attained with one hundred percent (100%) mortality for the control fish, those who received no AMP treatment. This means that both in vivo and in vitro assay supported the premise that the two cathelicidin AMPs were effective in increasing the survival of the catfish.  

In conclusion, the antimicrobial peptides cathelicidin which were derived from alligator and sea snake have shown effective antimicrobial capacity to inhibit major catfish pathogens in vitro. It also enhanced the protection of both types of catfish from virus immersion challenges. There are also different ways in order to deliver the peptide, it may be through injection, feed, or the development of transgenic fish which is capable of producing cathelicidin and the latter is the most economically feasible option. 

What Now? Here in the Philippines, catfish species are known to be disease-resilient. But the truth is, it is also very prone to diseases and their bacterial pathogens are not of research interest as of this time here in the country. But maybe in the near future, research will be geared towards disease prevention of other aquacultural commodities. Reducing the disease occurrences in the aquaculture industry could result in the reduction of economic losses. Having integrated approaches to control these is truly a desirable action towards a more sustainable and resilient aquaculture industry. 

Find out more about this journal article at: https://doi.org/10.1002/aah.10131