Vibrio mimics is an important aquatic pathogen that causes epidemics of fish vibriosis. With the abuse of antibiotics, the drug resistance of V. mimics has greatly increased, causing a poor therapeutic effect. It is particularly important to develop antibiotic alternatives against resistant bacteria. Beta-defensins (BDs) are a family of cysteine-rich and cationic antimicrobial peptides that play a crucial role in host defense against bacterial diseases. Herein, BD1 derived from Ctenopharyngodon idella (CiBD1) was expressed through genetic engineering technology, and in vitro, the recombinant CiBD1 (rCiBD1) had a high anti-V. mimics activity with a minimum inhibitory concentration (MIC) value of 19.63 mu g/mL and a negligible toxicity against the tested cells within 6 x MIC concentration range. Subsequently, in vivo antibacterial effect of CiBD1 was evaluated, showing CiBD1 overexpression could significantly improve the survival rate of V. mimics-challenged C. idella, and accompanied by reduced tissue bacterial load and histological lesions. Finally, the action mechanism of rCiBD1 was explored using ONPG assay, SEM observation, Gel retardation assay, and SDS-PAEG analysis, respectively. These assays indicated that rCiBD1 could damage the integrity of V. mimics cell membrane and increase its permeability, bind to the bacterial genomic DNA, and inhibit the bacterial protein synthesis. The results of the present study confirmed that CiBD1 may exert a high anti-V. mimics effects via multi-target mechanism of action, and CiBD1 has the potential to be an antibiotics alternative against V. mimics infection in aquaculture.
