Edwardsiella piscicida Ail1: An outer membrane protein required for host infection

Edwardsiella piscicida is a significant pathogenic microorganism, and can lead to systematic infections in multifold hosts, including teleost, amphibians, and mammals. Ail is a surface protein involved in virulence. However, the underlining mechanism is still to be investigated in E. piscicida. This study examined the functions and immunoprotective properties of an Ail molecule from E. piscicida. Ail1 possessed a conserved Ail/Lom superfamily domain and was exposed to the bacterial surface. Mutation of ail1 significantly reduced the survival rate under acid and oxidizing environment, motility, biofilm formation, cellular infection, tissue dissemination, and causing mortality in infected fish. The loss abilities of TX01 Delta ail1 were rescued by overexpression of the ail1 gene. Recombinant Ail1 (rAil1) could interact with peripheral blood leukocytes from Japanese flounder and affect E. piscicida infection in vitro. Vaccine trial showed that rAil1 was used as a potential subunit vaccine and could induce effective immune protection against E. piscicida infection. Fish vaccinated with rAil1 produced the specific antibody against rAil1 in serum, which increased the bactericidal activity of serum complement. In addition, rAil1-vaccinated fish displayed the higher ROS and acid phosphatase activity of macrophages. The above findings indicated that Ail1 played a pivotal role in the virulence of E. piscicida and may be explored as a subunit vaccine in aquaculture.