Activity of the antimicrobial polypeptide piscidin 2 against fish ectoparasites

Abstract

The antiparasitic effects of piscidin 2, an antimicrobial polypeptide (AMPP) first isolated from mast cells of hybrid striped bass, were tested against three protistan ectoparasites of marine fish (the ciliates Cryptocaryon irritans and Trichodina sp., and the dinoflagellate Amyloodinium ocellatum) and one ciliate ectoparasite of freshwater fish (Ichthyophthirius multifiliis). I. multifiliis was the most susceptible parasite, with all theronts killed at 6.3 microg mL(-1) piscidin 2. The most resistant parasite was Trichodina, where a few cells were killed at 12.5 microg mL(-1), but several were still alive even at 100 microg mL(-1). C. irritans was of intermediate sensitivity, with some theronts killed at 12.5 microg mL(-1) and all killed at 25 microg mL(-1). High parasite density apparently exhausted the piscidin 2 before it could attain its maximal effect, but surviving parasites were often visibly damaged. The lower efficacy of piscidin 2 against marine parasites compared with the freshwater ciliate might be related to the inhibitory effects of high sea water cation levels. The tissue concentration of piscidins estimated in healthy hybrid striped bass gill (40 microg mL(-1)) suggests that piscidin 2 is lethal to the parasites tested at physiological concentrations and is thus an important component of innate defence in fish expressing this type of AMPP.

Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

“…According to Murray et al [51], mast cells could be directly involved in the destruction of pathogens and they provide further evidence for their multifunctional role in teleosts. Investigations have shown that mast cells of fish intestine and gills are involved in the production of specific AMPs, namely pleurocidin [51] and piscidins [21,23,30,33,61]. Piscidins have potent, broadspectrum antifungal and antibacterial activity and recently been found to have strong antiparasitic activity and were reported in gills of fish infected with three protistan ectoparasites [21], gills parasitized with a copepod [16], and gills infected with a monogenean [27].…”

“…Piscidins are the prototypical AMP present in piscine MCs [16,21e23,27,29e31]. Piscidins have potent, broad-spectrum antibacterial and antifungal activity and have strong antiparasitic activity [16,21,27]. With regard to their mechanism of action, piscidins are thought to inhibit the synthesis of the cell wall, nucleic acids, and proteins or even inhibit enzymatic activity [32].…”

Quantitative PCR assay for the detection of the parasitic ciliate Cryptocaryon irritans

“…Various protective measures such as chemical, physical, and immunological methods have been developed to cure the disease caused by C. irritans [2][3][4][5]. Although these methods appear to be useful in a closed system such as an aquarium, in an open system such as the natural environment they are difficult to apply and/or are not very efficient.…”

Immune protection of Mozambique tilapia (Oreochromis mossambicus) exposed to different infectious doses of ectoparasite (Cryptocaryon irritans)

“…Thus, our results suggest that the potential involvement of innate immunity in the immobilization activities should also be considered, even when the serum was heat-inactivated. Colorni et al (2008) reported that piscidin three, an antimicrobial polypeptide, isolated from mast cells of hybrid striped bass was involved in immobilization responses and lethal to C. irritans theronts. It is not yet clear if other humoral factors such as complement, antimicrobial polypeptides, lysozyme, and lectins were boosted after the secondary exposure and resulted in higher immobilization titre compared to those post primary exposure.…”