ArnB mediates CAMP resistance and in vivo colonization in the fish pathogen Edwardsiella piscicida

Adoption of a live attenuated vaccine (LAV) will be an effective disease management strategy in farmed fish. Given the natural existence of cationic antimicrobial peptides (CAMP) in fish, the CAMP susceptible strain has been a promising LAV candidate against the bacterial disease of fish. Edwardsiella piscicida, the aetiological agent of fish edwardsiellosis, has caused massive economic losses in aquaculture industries. However, the mechanism underlying the CAMP resistance of E. piscicida is not entirely clear. In this study, the arnB gene was identified to contribute to E. piscicida resistance to CAMP, such as polymyxin B and polymyxin E. The expression of arnB was inhibited by Mg2+ ions and activated by PhoP. Moreover, Delta arnB had impaired capability for in vivo colonization and had reduced virulence in turbot. Together, our findings demonstrated that arnB was required for CAMP resistance and in vivo colonization in E. piscicida, suggesting that Delta arnB might be a prospective potential LAV candidate against edwardsiellosis.