Common carp (Cyprinus carpio) blood cells are modulated by a parasitic antimicrobial peptide, A-2S and Edwardsiella spp. strains.

Aquaculture industry faces significant challenges due to edwardsiellosis, a bacterial disease caused by Edwardsiella species, particularly E. tarda, which leads to high mortality in farmed fish and consequent financial losses. This pathogen, opportunistic in nature, becomes virulent under unsuitable conditions for fish, causing severe tissues damage in the host. Antibiotic treatments are increasingly ineffective due to Edwardsiella antibiotic resistance, necessitating alternative solutions. This for, we tested the antimicrobial efficiency of the cecropin anisaxin-2S (A-2S), an antimicrobial peptide (AMP) isolated from marine nematodes Anisakis simplex and A. pegreffii against six Edwardsiella spp. and their strains (in total 11). Based on the significant differences in the observed antimicrobial activity, E. tarda strain ET20 (fish isolate, A-2S resistant) and DSM 30052 (human isolate, A-2S sensitive) were further in vitro tested in the common carp (Cyprinus carpio) white and red blood cells treated with anisaxin-2S. A-2S significantly stimulated the production of ROS by erythrocytes and leukocytes challenged with both strains, contributing to a higher cell survival, compared to A-2S non-treated blood cells exposed to bacteria. Pro-inflammatory response was equally expressed in both cell types upon stimulation with E. tarda strains but has been further amplified upon A-2S treatment. A-2S alone induced significant upregulation of il-1β in both cell types and time points. The strong antimicrobial activity and immunostimulatory properties of this anisaxin justify further trials against edwardsiellosis.