Three naturally occurring host defense peptides protect largemouth bass (Micropterus salmoides) against bacterial infections

Abstract Infectious diseases caused by drug-resistant bacteria are big challenges for aquaculture industry. Innovative anti-infective drugs and/or therapeutic strategies are urgently needed. Host defense peptides (HDPs) are naturally occurring peptides that are regarded as promising alternatives to conventional antibiotics. However, their application as antimicrobial agents in aquaculture has not been well studied. In the present study, three previously characterized HDPs (CATHPb1, Cm-CATH2, and Hc-CATH) were selected and their protective ability on largemouth bass (Micropterus salmoides) against bacterial infections was determined. The three HDPs exhibited potent and broad-spectrum antimicrobial activity against aquatic pathogenic bacteria, with MIC values ranging 2.34–18.75 μg/ml. They rapidly kill bacteria within 30 min by inducing cytomembrane permeabilization and cell disruption. They also showed strong ability to inhibit the formation of bacterial biofilms and eradicate the preformed biofilms, which enable them with great potential to combat biofilm-related infections. Besides, they could effectively modulate the anti-infective immune responses of largemouth bass by simultaneously inhibiting the expression of pro-inflammatory cytokines (TNF-α and IL-1β) and stimulating the expression of chemokine IL-8. Animal challenge test proved that they could significantly enhance the survival rate of bacteria-challenged largemouth bass from less than 40% to over 60% and remarkably decrease the in vivo bacterial numbers. Moreover, compared to the conventional antibiotics, they showed dramatically lower propensity to induce bacterial resistance. All the results above imply the great potential of the three HDPs as novel anti-infective agents in largemouth bass culture.