Exploring Antibacterial Activity of Fish Protein Hydrolysate In Vitro Against Strains and Disease Resistance to in Turbot ().

This study was to investigate the in vitro antimicrobial activity of fish protein hydrolysate (FPH) against , , and , as well as the nonspecific immunity, intestinal microbiota, and disease resistance to in turbot. FPH was prepared from Pollock. The antibacterial activity of FPH was measured by the agar well diffusion, turbidometric assay, and plate count. The feeding trial was performed to study the effect of FPH on the resistance against in turbot after feeding three diets containing a high level of fish meal (FM), a high level of soybean meal (SM), and 100 g/kg FPH. Agar well diffusion showed the clearest inhibition zone of FPH was observed against , followed by . The bacterial growth curve and plate count showed a slight antibacterial effect of FPH against . Results of the feeding trial showed that FPH enhanced antioxidant and immune responses before challenge as modulating immunoglobulin M (IgM), catalase (CAT), and myeloperoxidase (MPO) activities in serum, as well as the number of goblet cells in the intestine. Meanwhile, the expression of some pro-inflammatory cytokines (interleukin-1 [], , and ) was downregulated in the FPH group after the challenge. Survival probability in the FPH group increased after challenging to based on the Kaplan-Meier analysis. Results of intestinal microbiota showed the relative abundance of in the SM group was the highest, followed by the FPH and control groups. Similarly, the relative abundance of distal intestinal was significantly reduced in the FPH group by analyzing the gene. In conclusion, the present FPH against strains was species-specific, with stronger antibacterial activity to . Dietary FPH enhanced the nonspecific immunity and antibacterial activity of turbot, increasing the resistance to .